Discovery of a small-molecule inhibitor for kidney ADP-ribosyl cyclase: Implication for intracellular calcium signal mediated by cyclic ADP-ribose

ADP-ribosyl cyclase (ADPR-cyclase) produces a Ca2+-mobilizing second messenger, cyclic ADP- ribose (cADPR), from beta-NAD+. A prototype of mammalian ADPR-cyclases is a lymphocyte antigen CD38. Accumulating evidence indicates that ADPR-cyclases other than CD38 are expressed in various cells and organs. In this study, we discovered a small molecule inhibitor of kidney ADPR-cyclase. This compound inhibited kidney ADPR-cyclase activity but not CD38, spleen, heart or brain ADPR-cyclase activity in vitro. Characterization of the compound in a cell-based system revealed that an extracellular calcium-sensing receptor (CaSR)- mediated cADPR production and a later long-lasting increase in intracellular Ca2+ concentration ([Ca2+]i) in mouse mesangial cells were inhibited by the pre-treatment with this compound. In contrast, the compound did not block CD3/TCR-induced cADPR production and the increase of [Ca2+]i in Jurkat T cells, which express CD38 exclusively. The long-lasting Ca2+ signal generated by both receptors was inhibited by pre-treatment with an antagonistic cADPR derivative, 8-Br-cADPR, indicating that the Ca2+ signal is mediated by the ADPR-cyclase metabolite, cADPR. Moreover, among structurally similar compounds tested, the compound inhibited most potently the cADPR production and Ca2+ signal induced by CaSR. These findings provide evidence for existence of a distinct ADPR-cyclase in the kidney and basis for the development of tissue specific inhibitors.     

High throughput fluorescence-based assays for cyclic ADP-ribose,NAADP, and their metabolic enzymes

Cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP) are two novel Ca(2+) messengers derived respectively from NAD and NADP. Since their discovery in sea urchin eggs, both have now been shown to serve messenger functions in a wide range of cells from plant to human. In this article, a series of fluorimetric assays for cADPR, NAADP and their metabolic enzymes is compiled. The enzyme assay makes use of an analog of NAD, nicotinamide guanine dinucleotide, which is non-fluorescent but is cyclized by the enzymes to a fluorescent analog of cADPR, cyclic GDP-ribose. Other NAD utilizing enzymes are not capable of catalyzing the cyclization and thus produce no interference. The fluorimetric assays for cADPR and NAADP make use of coupled-enzyme amplification and can readily detect nanomolar concentrations of either messenger. All the assays described can be performed in multi-well format, allowing ready automation and use in high throughput screening. An added advantage of these assays is that all the required reagents are commercially available, facilitating general adoption of the techniques by all those who are interested in the physiology and enzymology of the novel Ca(2+) signaling pathways mediated by cADPR and NAADP.     

Mechanism of action of choleragen.

Choleragen exerts its effect on cells through activation of adenylate cyclase. Choleragen initially interacts with cells through binding of the B subunit of the toxin to the ganglioside GM1 on the cell surface. Subsequent events are less clear. Patching or capping of toxin on the cell surface may be an obligatory step in choleragen action. Studies in cell-free systems have demonstrated that activation of adenylate cyclase by choleragen requires NAD. In addition to NAD, requirements have been observed for ATP, GTP, and calcium-dependent regulatory protein. GTP also is required for the expression of choleragen-activated adenylate cyclase. In preparations from turkey erythrocytes, choleragen appears to inhibit an isoproterenol-stimulated GTPase. It has been postulated that by decreasing the activity of a specific GTPase, choleragen would stabilize a GTP-adenylate cyclase complex and maintain the cyclase in an activated state. Although the holotoxin is most effective in intact cells, with the A subunit having 1/20th of its activity and the B subunit (choleragenoid) being inactive, in cell-free systems the A subunit, specifically the A1 fragment, is required for adenylate cyclase activation. The B protomer is inactive. Choleragen, the A subunit, or A1 fragment under suitable conditions hydrolyzes NAD to ADP-ribose and nicotinamide (NAD glycohydrolase activity) and catalyzes the transfer of the ADP-ribose moiety of NAD to the guandino group of arginine (ADP-ribosyltransferase activity). The NAD glycohydrolase activity is similar to that exhibited by other NAD-dependent bacterial toxins (diphtheria toxin, Pseudomonas exotoxin A), which act by catalyzing the ADP-ribosylation of a specific acceptor protein. If the ADP-ribosylation of arginine is a model for the reaction catalyzed by choleragen in vivo, then arginine is presumably an analog of the amino acid which is ADP-ribosylated in the acceptor protein. It is postulated that choleragen exerts its effects on cells through the NAD-dependent ADP-ribosylation of an arginine or similar amino acid in either the cyclase itself or a regulatory protein of the cyclase system.     

Use of high-performance liquid chromatography for assay of glutamic acid decarboxylase. Its limitation in use for post-mortem brain.

Rat brain, obtained 10 min after death, contained high levels of endogenous gamma-aminobutyric acid (GABA) and glutamic acid. Incubation of this brain homogenate at 37 degrees C indicated decrease of GABA with time due to degradation by GABA-transaminase. Reported high-performance liquid chromatographic (HPLC) methods for glutamic acid decarboxylase (GAD) assay depend on the difference between the GABA content of the reaction mixture after and before the incubation period. None of the methods considered the degradation of GABA during incubation. Furthermore, during determination of the Michaelis constant (KM) for the reaction none of them considered the endogenous substrate. Here we have focused on these factors which seriously affect the maximum velocity (Vmax) and KM values during GAD assay by the HPLC technique. By a simple and rapid HPLC technique we have measured GAD activity in post-mortem rat brain after removing endogenous glutamic acid by charcoal treatment and using gabaquline to prevent GABA degradation during incubation period. By this method a Vmax value of 46 +/- 4 nmol/h/mg protein and a KM value of 7.5 +/- 0.6 mM were observed for GAD activity of crude brain homogenate. For a comparative study, we have carried out radiometric assay of GAD activity from the same sample and observed a Vmax of 48 +/- 6 nmol/h/mg protein and KM of 6.9 +/- 0.4 mM.     

The development of an immobilized enzyme reactor containing glyceraldehyde-3-phosphate dehydrogenase from Trypanosoma cruzi: the effect of species' specific differences on the immobilization

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) plays an important role in the life cycle of the Trypanosoma cruzi, and an immobilized enzyme reactor (IMER) has been developed for use in the on-line screening for GAPDH inhibitors. An IMER containing human GAPDH has been previously reported; however, these conditions produced a T. cruzi GAPDH-IMER with poor activity and stability. The factors affecting the stability of the human and T. cruzi GAPDHs in the immobilization process and the influence of pH and buffer type on the stability and activity of the IMERs have been investigated. The resulting T. cruzi GAPDH-IMER was coupled to an analytical octyl column, which was used to achieve chromatographic separation of NAD(+) from NADH. The production of NADH stimulated by d-glyceraldehyde-3-phosphate was used to investigate the activity and kinetic parameters of the immobilized T. cruzi GAPDH. The Michaelis-Menten constant (K(m)) values determined for d-glyceraldehyde-3-phosphate and NAD(+) were K(m) = 0.5 +/- 0.05 mM and 0.648 +/- 0.08 mM, respectively, which were consistent with the values obtained using the non-immobilized enzyme.     

Chiral CE of aromatic amino acids by ligand-exchange with zinc(II)-L-lysine complex

A novel method of chiral ligand-exchange CE was developed with either L- or D-lysine (Lys) as a chiral ligand and zinc(II) as a central ion. This type of chiral complexes was explored for the first time to efficiently separate either individual pairs of or mixed aromatic amino acid enantiomers. Using a running buffer of 5 mM ammonium acetate, 100 mM boric acid, 3 mM ZnSO(4) x 7H(2)O and 6 mM L-Lys at pH 7.6, unlabeled D,L-tryptophan, D,L-phenylalanine, and D,L-tyrosine were well separated, giving a chiral resolution of up to 7.09. The best separation was obtained at a Lys-to-zinc ratio of 2:1, zinc concentration of 2-4 mM and running buffer pH 7.6. The buffer pH was determined to have a strong influence on resolution, while buffer composition and concentration impacted on both the resolution and peak shape. Boric acid with some ammonium acetate was an adoptable buffer system, and some additives like ethylene diamine tetraacetic acid capable of destroying the complex should be avoided. Fine-tuning of the chiral resolution and elution order was achieved by regulating the ratio of L-Lys to D-Lys; i.e. the resolution increased from zero to its highest value as the ratio ascended from 1:0 to 1:infinitive, and L-isomers eluted before or after D-isomers in excessive D- or L-Lys, respectively.     

Carbohydrate-lipid interactions: affinities of methylmannose polysaccharides for lipids in aqueous solution

The interactions between 3-O-methyl-mannose polysaccharides (MMPs), extracted from Mycobacterium smegmatis (consisting of a mixture of MMP-10, -11, -12 and -13) or obtained by chemical synthesis (MMP-5(s) , -8(s) , -11(s) and -14(s) ), and linear saturated and unsaturated fatty acids (FAs), and a commercial mixture of naphthenic acids (NAs) in aqueous solution at 25?°C and pH?8.5 were quantified by electrospray ionization mass spectrometry (ESI-MS). Association constants (K(a) ) for MMP binding to four FAs (myristic acid, palmitic acid, stearic acid and trans-parinaric acid) were measured by using an indirect ESI-MS assay, the "proxy protein" method. The K(a) values are in the 10(4) -10(5) M(-1) range and, based on results obtained for the binding of the synthetic MMPs with palmitic acid, increase with the size of the carbohydrate. Notably, the measured affinity of the extracted MMPs for trans-parinaric acid is two orders of magnitude smaller than the reported value, which was determined by using a fluorescence assay. Using a newly developed competitive binding assay, referred to as the "proxy protein/proxy ligand" ESI-MS method, it was shown that MMPs bind specifically to NAs in aqueous solution, with apparent affinities of approximately (5×10(4) )?M(-1) for the mixture of NAs tested. This represents the first demonstration that MMPs can bind to hydrophobic species more complex than those containing linear alkyl/alkenyl chains. Moreover, the approach developed here represents a novel method for probing carbohydrate-lipid interactions.     

Rapid determination of creatine, phosphocreatine, purine bases and nucleotides (ATP, ADP, AMP, GTP, GDP) in heart biopsies by gradient ion-pair reversed-phase liquid chromatography.

A simple binary solvent method has been developed for the simultaneous determination of creatine (Cr), phosphocreatine (PCr), ATP, ADP, AMP, GTP, GDP, IMP, NAD, inosine, adenosine, hypoxanthine and xanthine. This allows separation of the most important nucleotides present in myocardial biopsies as, for example, in studies using 31P NMR spectroscopy. In NMR spectra ATP and PCr are the only visible high-energy phosphates, therefore the status of other nucleotides and bases cannot be determined. The nucleotides, AMP degradation products, PCr and Cr in pig and rat heart muscle were resolved with 35 mM K2HPO4, 6 mM tetrabutylammonium hydrogensulfate buffer, pH 6.0, and a binary acetonitrile gradient on medium-bore, 250 mm or 125 mm x 3.9-4.6 mm I.D. steel octadecyl-bonded (C18) columns at a flow-rate of 1.5 or 1.0 ml/min. This method, optimized for use with older high-performance liquid chromatography pumps (100 microliters displacement heads), resolves the major porcine and rat myocardial nucleotides and degradation products within 22 min. The amounts found in normoxic porcine muscle are: Cr 9.21 +/- 0.75; hypoxanthine 1.40 +/- 0.14; PCr 7.20 +/- 1.2; IMP 1.34 +/- 0.13; beta NAD 1.82 +/- 0.23; AMP 0.10 +/- 0.04; GDP 0.05 +/- 0.02; ADP 1.23 +/- 0.09; GTP 0.19 +/- 0.01; ATP 4.45 +/- 0.32 mumol/g wet weight. The method, incorporating adenosine tetraphosphate as an internal standard, allows the documentation of changes in both the high-energy phosphates and their degradation products in a single analysis of myocardial samples as small as 200 micrograms (wet weight).     

Reagentless amperometric formaldehyde-selective biosensors based on the recombinant yeast formaldehyde dehydrogenase

Novel formaldehyde-selective amperometric biosensors were developed based on NAD(+)- and glutathione-dependent formaldehyde dehydrogenase isolated from a gene-engineered strain of the methylotrophic yeast Hansenula polymorpha. Electron transfer between the immobilized enzyme and a platinized graphite electrode was established using a number of different low-molecular free-diffusing redox mediators or positively charged cathodic electrodeposition paints modified with Os-bis-N,N-(2,2'-bipyridil)-chloride ([Os(bpy)(2)Cl]) complexes. Among five tested Os-containing redox polymers of different chemical structure and properties, complexes of osmium-modified poly(4-vinylpyridine) with molecular mass of about 60 kDa containing diaminopropyl groups were selected. The positively charged cathodic paint exhibited the best electron-transfer characteristics. Moreover, the polymer layers simultaneously served as a matrix for keeping the negatively charged low-molecular cofactors, glutathione and NAD(+), in the bioactive layer. Additionally, covering the enzyme/polymer layer with a negatively charged Nafion membrane significantly decreased cofactors leakage and simultaneously enhanced the sensor' stability. The developed sensors revealed a high selectivity to formaldehyde (FA) and a low cross-sensitivity to other substances (such as, e.g. butyraldehyde, propionaldehyde, acetaldehyde, methylglyoxal). The maximum current value was 34.2+/-0.72 microA/mm(2) (3.05 mm diameter electrode) and the apparent Michaelis-Menten constant (K(M)(app)) derived from the FA calibration curves was 120+/-5mM with a linear detection range for FA up to 20mM. The best observed sensitivity for reagentless sensor was 1.8 nA microM(-1) (358 Am(-2)M(-1)). The developed sensors had a good operational and storage stability. The laboratory prototype of the sensor was applied for FA testing in some real samples of pharmaceutical (formidron), disinfectant (descoton forte) and industrial product (formalin). A good correlation was revealed between the concentration values measured using the developed FdDH-based sensor, an enzymatic method and standard chemical methods of FA determination.     

Modifications to increase the efficiency of the fluorometric cycling assay for cyclic ADP-ribose

Cyclic ADP-ribose (cADPR) is an intracellular messenger that triggers the release of calcium ions from intracellular stores in a variety of cell types. The fluorometric cycling assay has become the preferred method for measuring cADPR due to its high level of sensitivity (in the sub-nanomolar range) and its use of commercially available reagents. Additionally, the assay is performed in multiwell plates, making it suitable for high throughput screening using a fluorescence plate reader. The findings reported in this paper present several problems that may be encountered during various stages of the assay, and provide solutions to these problems. Modifications to the assay address reduced recovery of sample and cADPR with removal of perchloric acid (PCA) using organic solvent, reduction in diaphorase activity with heat treatment, and effects on resorufin fluorescence by pH range. Using these modifications, we report an increase of approximately 15% in recovery of brain cADPR, and show that between-subject variability is greatly reduced. We hope that these observations will encourage more widespread application of this valuable assay.     

Development and characterization of an immobilized enzyme reactor (IMER) based on human glyceraldehyde-3-phosphate dehydrogenase for on-line enzymatic studies

Immobilized enzyme reactors (IMERs) for on-line enzymatic studies are useful tool to select specific inhibitors and may be used for direct determination of drug-receptor binding interactions and for the rapid on-line screening to identify specific inhibitors. This technique has been shown to increase the stability of enzymes. The enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) plays an important role in the life cycle of the Trypanosoma cruzi and it has become a key target in the drug discovery program for Chagas' disease. Crystallographic studies have indicated that there are significant inter-species differences in GAPDH activity and sensitivity. For example the active sites of GAPDH in T. cruzi and humans differ by a substitution of ASP(210) (T. cruzi) by Leu(194) in human. Based on this information we initiated the study to develop optimal conditions for the covalent immobilization of the human GAPDH enzyme on a modified capillary support (400 mm x 0.10 mm). The chromatographic separation of NAD from NADH was achieved using a RP-Spherex-diol-OH (10 cm x 0.46 cm, 10 microm, 100 A) column. By using multidimensional HPLC chromatography system it was possible to investigate the activity and kinetic parameters of the GAPDH-IMER. The values obtained for D-GA3P and NAD were K(m)=3.5+/-0.2 mM and 0.75+/-0.04 mM, respectively, and were compared with values obtained with the free enzyme. The activity of the immobilized GAPDH has been preserved for over 120 days.     

Assay of Angiotensin I-converting Enzyme-inhibiting Activity Based on the Detection of 3-Hydroxybutyrate with Water-soluble Tetrazolium Salt.

A newly synthesized substrate, 3-hydroxybutyrylglycyl-glycyl-glycine (3HB-GGG), was applied to the assay of ACE-inhibiting activity to overcome the smaller selectivity and sensitivity of the conventional method. In this study, an ACE-inhibiting assay was improved by the use of a water-soluble tetrazolium salt, 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate sodium salt (WST-1), for the detection of 3-hydroxybutyrate, derived from 3HB-GGG. The optimized conditions were as follows: 0.333 mM NAD(+), 0.333 mM WST-1, 0.1 mM EDTA, 0.633 U ml(-1) diaphorase, and 0.700 U ml(-1) 3-hydroxybutyrate dehydrogenase. The developed assay was efficiently applicable to evaluate the ACE-inhibiting activity of practical ACE inhibitors.     

The HLB dependency for detergent solubilization of hormonally sensitive adenylate cyclase.

The HLB dependency for the solubilization of membrane proteins and adenylate cyclase activity from a plasma membrane-enriched fraction from rat liver has been determined. The HLB (hydrophilic/lipophilic/balance) number of a detergent is an empirical measure of its relative hydrophobicity. Detergent HLB numbers vary systematically with the length of the ethylene oxide chain for a homologous series of detergents such as the Triton X series. These detergents have a constant hydrophobic moiety, octylphenyl, and a variable polar portion, polyethoxyethanol. Basal-NaF-epinephrine-, and glucagon-stimulated adenylate cyclase activities were solubilized in the HLB range of 16.8-17.4. Solubilization was most effective in 0.01 M Tris buffers at pH 7.5 containing 1-5 mM mercaptoethanol, 1 mM MgCl2, and 0.1% Triton X-305. The detergent to membrane protein ratio used in these studies was 3:1. Criteria for solubilization included lack of sedimentation at 100,000 X g, the absence of particulate material in the supernatant when examined by electron microscopy, and inclusion of hormonally sensitive adenylate cyclase activity in Sephadex G-200 gels. The apparent molecular weight of the solubilized enzyme was approximately 200,000 in the presence of Triton X-305. The solubilized enzyme was stimulated 5-fold by NaF, 7-fold by glucagon, and 20-fold by epinephrine compared to the particulate enzyme used in this study which was stimulated 10-fold, 3.4-fold, and 4-fold by NaF, epinephrine, and glucagon, respectively. The solubilized enzyme is stable for several weeks when stored at -60 degrees C.     

Slowing of cisplatin aquation in the presence of DNA but not in the presence of phosphate: improved understanding of sequence selectivity and the roles of monoaquated and diaquated species in the binding of cisplatin to DNA

1H-15N HSQC NMR spectroscopy is used to study the aquation reactions of cisplatin in 9 mM NaClO4 and 9 mM phosphate (pH 6) solutions at 298 K. For the first time in a single reaction and, therefore, under a single set of reaction conditions, the amounts of all species formed are followed and the rates of aquation, diaquation, and related anation processes are determined in both media. Binding of phosphate to aquated Pt species is observed, but the initial rate of aquation is not affected by the presence of 9 mM phosphate. The reaction between cisplatin and the 14-base-pair self-complementary oligonucleotide 5'-d(AATTGGTACCAATT)-3', having a GpG intrastrand binding site, is investigated. Various kinetic models for this reaction are evaluated and the most appropriate found to be that with a reversible aquation step and a single binding site for the self-complementary duplex. The rate constant for aquation is (1.62 +/- 0.02) x 10(-5) s-1, with the anation rate constant fixed at 4.6 x 10(-3) M-1 s-1, the value obtained from the aquation studies. The rate constants for monofunctional binding of cis-[PtCl(15NH3)2-(OH2)]+ to the sequence were 0.48 +/- 0.19 and 0.16 +/- 0.06 M-1 s-1 for the 3'- and 5'-guanine bases, respectively. Closure rate constants for the monofunctional adducts are (2.55 +/- 0.07) x 10(-5) and (0.171 +/- 0.011) x 10(-5) s-1, for the 3'- and 5'-guanines, respectively. The presence of DNA slows the aquation of cisplatin by 30-40% compared to that observed in 9 mM NaClO4 or 9 mM phosphate, and there is some evidence that the degree of slowing is sequence dependent. The possibility that cis-[Pt(OH)(NH3)2(OH2)]+ contributes to the binding of cisplatin to DNA is investigated, and it is found that about 1% followed this route, the majority of the binding occurring via the monoaquated species cis-[PtCl(NH3)2(OH2)]+. Comparison of the rates of disappearance of cisplatin in reactions at single defined GpG, ApG, GpA, GpTpG and 1,2-interstrand GG binding sites shows that the adduct profile is determined at the level of monofunctional adduct formation.     

Determination of egg white lysozyme by on-line coupled capillary isotachophoresis with capillary zone electrophoresis

An on-line coupled capillary isotachophoresis - capillary zone electrophoresis method for the determination of lysozyme in selected food products is described. The optimized electrolyte system consisted of 10 mM NH(4)OH + 20 mM acetic acid (leading electrolyte), 5 mM epsilon -aminocaproic acid +5 mM acetic acid (terminating electrolyte), and 20 mM epsilon -aminocaproic acid +5 mM acetic acid +0.1% m/v hydroxypropylmethylcellulose (background electrolyte). A clear separation of lysozyme from other components of acidic sample extract was achieved within 15 min. Method characteristics, i.e., linearity (0-50 micrograms/mL), accuracy (recovery 96+/-5%), intra-assay (3.8%), quantification limit (1 microgram/ml), and detection limit (0.25 microgram/mL) were determined. Low laboriousness, sufficient sensitivity and low running costs are important attributes of this method. The developed method is suitable for the quantification of the egg content in egg pasta.     

Comparative studies of the interaction between ferulic acid and bovine serum albumin by ACE and surface plasmon resonance

Affinity capillary electrophoresis (ACE) was used to study the interaction between ferulic acid (FA) and BSA. The interaction between FA and BSA was facilitated by injecting FA into a BSA-containing running buffer. Both mobility ratio and mobility shift assays were performed to deduce the binding constant (K(b)). However, the K(b )value obtained with the mobility ratio assay was only approximately 20% of that extracted from the mobility shift assay. The former assay yielded a K(b) value (5.6 +/- 0.4 x 10(4) M(-1)), which compares well with the result obtained with surface plasmon resonance (SPR) (5.1 +/- 0.6 x 10(4) M(-1)). The discrepancy between the mobility ratio and mobility shift assays suggests that the data extrapolation from the mobility ratio should be more reliable for cases when both changes in the EOF and viscosity of the running buffer are important. The work demonstrates that ACE, a solution-based technique, and SPR, a technique addressing interfacial processes, are highly complementary to each other and the comparative studies are confirmatory and allow binding constants to be accurately determined.     

Electrical contacting of flavoenzymes and NAD(P)+-dependent enzymes by reconstitution and affinity interactions on phenylboronic acid monolayers associated with Au-electrodes

The preparation of integrated, electrically contacted, flavoenzyme and NAD(P)(+)-dependent enzyme-electrodes is described. The reconstitution of apo-glucose oxidase, apo-GOx, on a FAD cofactor linked to a pyrroloquinoline quinone (PQQ) phenylboronic acid monolayer yields an electrically contacted enzyme monolayer (surface coverage 2.1 x 10(-)(12) mol cm(-)(2)) exhibiting a turnover rate of 700 s(-)(1) (at 22 +/- 2 degrees C). The system is characterized by microgravimetric quartz-crystal microbalance analyses, Faradaic impedance spectroscopy, rotating disk electrode experiments, and cyclic voltammetry. The performance of the enzyme-electrode for glucose sensing is described. Similarly, the electrically contacted enzyme-electrodes of NAD(P)(+)-dependent enzymes malate dehydrogenase, MalD, and lactate dehydrogenase, LDH, are prepared by the cross-linking of affinity complexes generated between the enzymes and the NADP(+) and NAD(+) cofactors linked to a pyrroloquinoline quinone phenylboronic acid monolayer, respectively. The MalD enzyme-electrode (surface coverage 1.2 x 10(-)(12) mol cm(-)(2)) exhibits a turnover rate of 190 s(-)(1), whereas the LDH enzyme-electrode (surface coverage 7.0 x 10(-)(12) mol cm(-)(2)) reveals a turnover rate of 2.5 s(-)(1). Chronoamperometric experiments reveal that the NAD(+) cofactor is linked to the PQQ-phenylboronic acid by two different binding modes. The integration of the LDH with the two NAD(+) cofactor configurations yields enzyme assemblies differing by 1 order of magnitude in their bioelectrocatalytic activities.     

Effect of AOT on enzymatic activity of the organic solvent resistant tyrosinase from Streptomyces sp. REN-21 in aqueous solutions and water-in-oil microemulsions

The effect of AOT (sodium-bis(2-ethylhexyl sulfosuccinate)) on enzymatic activity of the organic solvent resistant tyrosinase (OSRT) in aqueous phosphate buffer solutions and in water-in-oil microemulsions of the water/AOT/isooctane system has been investigated. In contrast to mushroom tyrosinase, AOT does not activate OSRT in aqueous solutions, altering its activity very little at concentrations lower than 2 mM. Increasing contents of AOT in isooctane reduce the observed initial reaction rates of oxidation of t-butylcatechol (tBC) and 4-methylcatechol (4-MC). Similarly to mushroom tyrosinase, the effect has been described using an equation based on preferential binding of the substrates by surfactant interface layers. The apparent Michaelis-Menten substrate binding constants increase linearly with AOT concentration (with slopes of 0.12+/-0.02 and 0.051+/-0.006 for tBC and 4-MC, respectively), and the effective enzyme turnover number in the microemulsions remains practically constant.     

烟酰胺腺嘌呤二核苷酸类CD38抑制剂的合成及生物活性评价

分别以1,3,5-三苯甲酰基-α-D-核糖、3,5-二苯甲酰基-2-脱氧-2,2-二氟戊呋喃糖-1-酮和D-木糖为原料, 经由烟酰胺核苷及烟酰胺核苷酸中间体, 合成了系列糖环经氟原子取代的烟酰胺腺嘌呤二核苷酸(NAD)类CD38抑制剂. 基于对CD38的水解抑制能力的考察, 评价了所合成氟代NAD类似物的活性. 结果表明, 糖环上氟原子取代的数目和位置对抑制剂活性的影响十分明显, 烟酰胺核苷的端基构型对活性的影响较大. 2个化合物均显示出非常好的CD38抑制活性, 其中化合物2a的抑制活性高出阳性对照物阿糖型氟代烟酰胺腺嘌呤二核苷酸2个数量级.     

Determination of glycyrrhizin in liqueurs by on-line coupled capillary isotachophoresis with capillary zone electrophoresis

An on-line coupled capillary isotachophoresis-capillary zone electrophoresis method for the determination of glycyrrhizin in liqueurs is described. The optimised electrolyte system was 5 mM HCl+11 mM varepsilon-aminocaproic acid+0.05% hydroxyethylcellulose+30% methanol (leading electrolyte), 5 mM caproic acid+30% methanol (terminating electrolyte) and 20 mM caproic acid+10 mM histidine+0.1% hydroxyethylcellulose+30% methanol (background electrolyte). Method characteristics, i.e., linearity (20-500 ng/ml), accuracy (recovery 99+/-4%), intra-assay repeatability (2%), intermediate repeatability (3.8%) and detection limit (8 ng/ml) were determined. Speed of analysis, low laboriousness, high sensitivity and low-running cost are the typical attributes of the capillary isotachophoresis-capillary zone electrophoresis method. Developed method was successfully applied to analysis of liqueurs with liquorice extract and some foods (sweets and food supplements) containing liquorice. Found levels of glycyrrhizin in liqueurs, sweets and food supplements varied between 1-16 mg/l, 850-1050 mg/kg and 1.6-1.8 g/kg, respectively.