Immobilization of Phenylalanine Dehydrogenase and Its Application in Flow-Injection Analysis System for Determination of Plasma Phenylalanine

Phenylalanine dehydrogenase (l-PheDH) from Sporosarcina ureae was immobilized on DEAE-cellulose, modified initially with 2-amino-4,6-dichloro-s-triazine followed by hexamethylenediamine and glutaraldehyde. The highest activity of immobilized PheDH was determined as 95.75 U/g support with 56% retained activity. The optimum pH value of immobilized l-PheDH was shifted from pH 10.4 to 11.0. The immobilized l-PheDH showed activity variations close to the maximum value in a wider temperature range of 45–55 °C, whereas it was 40 °C for the native enzyme. The pH and the thermal stability of the immobilized l-PheDH were also better than the native enzyme. At pH 10.4 and 25 °C, K _m values of the native and the immobilized l-PheDH were determined as K _{m Phe} = 0.118, 0.063 mM and K _{m NAD}⁺ = 0.234, 0.128 mM, respectively. Formed NADH at the exit of packed bed reactor column was detected by the flow-injection analysis system. The conversion efficiency of the reactor was found to be 100% in the range of 5–600 μM Phe at 9 mM NAD⁺ with a total flow rate of 0.1 mL/min. The reactor was used for the analyses of 30 samples each for 3 h per day. The half-life period of the reactor was 15 days.     

Determination of the Enantiomeric Purity of l-Carnitine and Acetyl-l-Carnitine by Chiral Liquid Chromatography

A chiral liquid chromatographic method for determination of the enantiomeric purity of both l-carnitine and acetyl-l-carnitine is described. Separation of the enantiomers of dl-carnitine and acetyl-dl-carnitine was achieved on a commercial chiral column (Chiralcel OD-R) after derivatization with (alpha-bromo)methyl phenyl ketone. Introduction of this lipophilic UV chromophoric group to the carnitine and acetylcarnitine molecules improved their retention, resolution, and UV detection. The mobile phase was 74:26 (v/v) 0.5 mol L^-1 sodium perchlorate–acetonitrile, pH 3.8, and the flow rate was 0.4 mL min^-1. Detection was performed at 235 nm. The method is selective and reliable for determination of the enantiomeric purity of bulk drug substances l-carnitine and acetyl-l-carnitine.     

Enzymatic preparation of optically active silicon-containing amino acids and their application

Optically active 3-trimethyl silylalanine (TMS-Ala) was prepared by hydrolysis of N-acetyl-dl-TMS-Ala catalyzed by acylase I (aminoacylase; N-acylamino-acid amidohydrolase, EC3.5.1.14). Acylase I from porcine kidney (PKA) was found to be more effective than that from Aspergillus melleus in the preparation of l-TMS-Ala. Under the optimized conditions, optically pure l-TMS-Ala (>99% enantiomeric excess, ee) was obtained with a 72% yield. Furthermore, a highly optically pure d-TMS-Ala (96% ee) could also be obtained with a 76% yield by chemical hydrolysis of the residual substrate. Enzymatic synthesis of peptides containing TMS-Ala was also attempted in ethyl acetate. Benzyloxycarbonyl (Z)-l-TMS-Ala served as the substrate for thermolysin, whereas l-TMS-Ala-OMe was inactive as the amino component. In the case of inhibitory activity of dipeptides toward thermolysin, l-Leu-(l-TMS-Ala) was found to be a more potent inhibitor than l-Leu-l-Leu, which is known to be one of the most effective inhibitors of thermolysin among the dipeptides consisting of natural aminoacids.     

Immobilization ofmyo-inositol-1-phosphate synthase containing active,self-regenerating coenzyme (NAD+) on the same matrix

myo-Inositol-1-phosphate synthase (EC 5.5.1.4) from rat testes, an NAD⁺-containing enzyme, which convertsd-glucose 6-phosphate to 1l-myo-inositol 1-phosphate, could be immobilized together with its cofactor and bovine serum albumin by crosslinking with glutaraldehyde at pH 4.5. The enzyme bound to the gel showed a specific activity of 5.6% of that of the native enzyme, but the activity could be increased to 21% by pretreatment with urea.     

Glycoconjugates of amino acids. Preparation throughN-alkylation of amino acids withN-chloroacetyl-β-glycopyranosylamines

Monoalkylation of amino acids of different structural types withN-chloroacetyl-glycosylamines was shown to be applicable for the preparation of glycoconjugates containing β-d-galactose,N-acetyl-β-d-glucosamine, β-d-mannose, and lactose residues. The glycoconjugates were synthesized from amino acids with secondary (sarcosine,l-proline) or primary (l-2- and 4-aminobutyric acids,l-tryptophan) amino groups as well as from various amino dicarboxylic acids (N-methyl-dl-aspartic,dl-aspartic,l-glutamic, anddl-2-aminoadipic acids). The derivatives obtained may be of interest for glycotargeting of physiologically active compounds of this series. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1377–1380, July, 1999.     

Production of 2-O-α-glucopyranosyl l-ascorbic acid from ascorbic acid and β-cyclodextrin using immobilized cyclodextrin glycosyltransferase

Cyclodextrin glycosyltransferase (CGTase) isolated and purified from Paenibacillus sp. A11 was immobilized on various carriers by covalent linkage using bifunctional agent glutaraldehyde. Among tested carriers, alumina proved to be the best carrier for immobilization. The effects of several parameters on the activation of the support and on the immobilization of enzyme were optimized. The best preparation of immobilized CGTase retained 31.2% of its original activity. After immobilization, the enzymatic properties were investigated and compared with those of the free enzyme. The optimum pH of the immobilized CGTase was shifted from 6.0 to 7.0 whereas optimum temperature remained unaltered (60°C). Free and immobilized CGTase showed similar pH stability profile but the thermal stability of the immobilized CGTase was 20% higher. Kinetic data (K _M and V _max) for the free and immobilized enzymes were determined from the rate of β-CD formation and it was found that the immobilized form had higher K _M and lower V _max. The immobilized CGTase also exhibited higher stability when stored at both 4°C and 25°C for 2 months. The enzyme immobilized on alumina was further used in a batch production of 2-O-α-glucopyranosyl-l-ascorbic acid (AA-2G) from ascorbic acid and β-cyclodextrin. The yield of AA-2G was 2.92% and the immobilized CGTase retained its activity up to 74.4% of the initial catalytic activity after being used for 3 cycles. The immobilized CGTase would have a promising application in the production of various transglycosylated compounds and in the production of cyclodextrin by the hydrolysis of starch.     

Continuous production of extracellular l-glutaminase by ca-alginate-immobilized marine Beauveria bassiana BTMF S-10 in packed-bed reactor

l-Glutamine amidohydrolase (l-glutaminase, EC 3.5.1.2) is a therapeutically and industrially important enzyme. Because it is a potent antileukemic agent and a flavor-enhancing agent used in the food industry, many researchers have focused their attention on l-glutaminase. In this article, we report the continuous production of extracellular l-glutaminase by the marine fungus Beauveria bassiana BTMF S-10 in a packed-bed reactor. Parameters influencing bead production and performance under batch mode were optimized in the order-support (Na-alginate) concentration, concentration of CaCl₂ for bead preparation, curing time of beads, spore inoculum concentration, activation time, initial pH of enzyme production medium, temperature of incubation, and retention time. Parameters optimized under batch mode for l-glutaminase production were incorporated into the continuous production studies. Beads with 12×10⁸ spores/g of beads were activated in a solution of 1% glutamine in seawater for 15 h, and the activated beads were packed into a packed-bed reactor. Enzyme production medium (pH 9.0) was pumped through the bed, and the effluent was collected from the top of the column. The effect of flow rate of the medium, substrate concentration, aeration, and bed height on continuous production of l-glutaminase was studied. Production was monitored for 5 h in each case, and the volumetric productivity was calculated. Under the optimized conditions for continuous production, the reactor gave a volumetric productivity of 4.048 U/(mL·h), which indicates that continuous production of the enzyme by Ca-alginate-immobilized spores is well suited for B. bassiana and results in a higher yield of enzyme within a shorter time. The results indicate the scope of utilizing immobilized B. bassiana for continuous commercial production of l-glutaminase.     

Production of <Emphasis Type="SmallCaps">d</Emphasis>-tagatose,a Functional Sweetener,Utilizing Alginate Immobilized <Emphasis Type="Italic">Lactobacillus fermentum</Emphasis> CGMCC2921 Cells

d-tagatose is a ketohexose that can be used as a novel functional sweetener in foods, beverages, and dietary supplements. This study was aimed at developing a high-yielding d-tagatose production process using alginate immobilized Lactobacillus fermentum CGMCC2921 cells. For the isomerization from d-galactose into d-tagatose, the immobilized cells showed optimum temperature and pH at 65 °C and 6.5, respectively. The alginate beads exhibited a good stability after glutaraldehyde treatment and retained 90% of the enzyme activity after eight cycles (192 h at 65 °C) of batch conversion. The addition of borate with a molar ratio of 1.0 to d-galactose led to a significant enhancement in the d-tagatose yield. Using commercial β-galactosidase and immobilized L. fermentum cells, d-tagatose was successfully obtained from lactose after a two-step biotransformation. The relatively high conversion rate and productivity from d-galactose to d-tagatose of 60% and 11.1 g l⁻¹ h⁻¹ were achieved in a packed-bed bioreactor. Moreover, lactobacilli have been approved as generally recognized as safe organisms, which makes this L. fermentum strain an attracting substitute for recombinant Escherichia coli cells among d-tagatose production progresses.     

Detection of halogenated organic compounds using immobilized thermophilic dehalogenase

Environmental pollutants containing halogenated organic compounds can cause a plethora of health problems. Detection, quantification, and eventual remediation of halogenated pollutants in the environment are important to human well-being. Toward this end, we previously identified a haloacid dehalogenase, L-HAD_ST, from the thermophile Sulfolobus tokodaii. This thermophilic enzyme is extremely stable and catalyzes, stereospecifically, the dehalogenation of l-2-haloacids. In the current study, we covalently linked L-HAD_ST to an N-hydroxysuccinimidyl Sepharose resin to construct a highly specific sensor with long shelf life for the detection of l-2-haloacids. The enzyme-modified resin was packed into disposable columns. Samples containing l-2-haloacids were first incubated in the column, and were then collected to quantify the chloride produced through the breakdown of the substrate. The optimum pH of the immobilized enzyme is around 9.5, similar to that of the soluble protein. Its catalytic activity increased with temperature up to the highest temperature measured (50 °C). The resin could be fully regenerated after multiple reaction cycles and retained 70% of the initial activity after being stored at 4 °C for 6 months. The L-HAD_ST-modified resin could be used to breakdown and quantify l-2-haloacids spiked in the simulated environmental samples, indicating dehalogenases from extremophiles can potentially be employed in the detection and decontamination of l-2-haloacids.     

Studies on crystals of <Emphasis Type="SmallCaps">d</Emphasis>-, <Emphasis Type="SmallCaps">l</Emphasis>-, and <Emphasis Type="SmallCaps">dl</Emphasis>-alaninato nickel(II) complexes

An attempt to link the heat of reaction obtained from analysis of UV spectra, bond energies deduced from crystallographic data and calorimetric measurements of [bis(d-, l-, and dl-alaninato)diaqua] nickel(II) dihydrate complexes to theoretical values obtained from calculation is described. The heat of reaction, which includes energy of ligand exchange in addition to crystal field stabilization energy of the three complexes, was calculated from changes in spectral shifts, bond lengths, and free energy between nickel(II) ion and the d-, l-, and dl-alanine complexed nickel(II) ion in aqueous solution. These investigations were done by UV–visible spectroscopy, X-ray crystallography, and isothermal calorimetry. The results reveal that the experimental heat of reaction based on the three mentioned parameters is in good agreement with the theoretical value. The results are found to be of considerable interest in its linking of spectrochemical quantities with thermodynamic functions.     

l-DOPA production by immobilized tyrosinase

The production of l-DOPA using l-tyrosine as substrate, the enzyme tyrosinase (EC 1.14.18.1) as biocatalyst, and l-ascorbate as reducing agent for the o-quinones produced by the enzymatic oxidation of the substrates was studied. Tyrosinase immobilization was investigated on different supports and chemical agents: chitin flakes activated with hexamethylenediamine and glutaraldehyde as crosslinking agent, chitosan gel beads, chitosan gel beads in the presence of glutaraldehyde, chitosan gel beads in the presence of polyvinyl pyrrolidone, and chitosan flakes using glutaraldehyde as crosslinking agent. The last support was considered the best using as performance indexes the following set of immobilization parameters: efficiency (90.52%), yield (11.65%), retention (12.87%), and instability factor (0.00). The conditions of immobilization on chitosan flakes were optimized using a two-level full factorial experimental design. The independent variables were enzyme-support contact time (t), glutaraldehyde concentration (G), and the amount of enzyme units initially offered (U _C). The response variable was the total units of enzymatic activity shown by the immobilized enzyme (U _IMO). The optimal conditions were t=24 h, G=2% (v/v), and U _C=163.7 U. Under these conditions the total units of enzymatic activity shown by the immobilized enzyme (U _IMO) was 23.3 U and the rate of l-DOPA production rate was 53.97 mg/(L·h).     

Trypsin-like enzyme fromStreptomyces 771

Electrophoretically homogenous proteolytic enzyme with molecular weight 31,500 and pI 3.75 was obtained from a culture medium ofStreptomyces 771 by chromatography onN-benzyl chitin adsorbent, subsequent chromatography on CM-cellulose, and preparative isofocusing and chromatography on Sephadex G-75. The enzyme hydrolyzesN- benzoyl-DL-arginine-p-nitroanilideN-benzoyl-DL-lysine-p-nitro-anilideN-benzoyl-DL-arginine ethyl ester, and Na-caseinate. It also exhibits pronounced thrombolytic activity. The activity of the enzyme was suppressed by soya bean inhibitor, but remained unaffected by chelating agents and phenylmethylsulfonyl fluoride. The enzyme was immobilized on aldehyde dextran, and some kinetic parameters of the immobilized enzyme were determined. The thrombolytic activity of native and immobilized enzyme was studied as well.     

Temperature- and pressure-responsive properties of <Emphasis Type="SmallCaps">l</Emphasis>- and<Emphasis Type="SmallCaps"> dl</Emphasis>-forms of poly(<Emphasis Type="Italic">N</Emphasis>-(1-hydroxymethyl)propylmethacrylamide) in aqueous solutions

The structural transition of the l- and dl forms of poly(N-(1- hydroxymethyl)propylmethacrylamide (PHMPMA) in aqueous solution was studied by measuring the pressure dependence of the apparent scattering intensity, differential scanning calorimetry (DSC), and circular dichroism (CD). The thermodynamic implications of the results are discussed in relation to the chiral structure of the side chain, and differences in the thermal and barometric transitions. T-P diagrams of the transition showed characteristic ellipsoid features. Antagonism of the temperature and pressure effects was observed only for P(dl-HMPMA). For P(l-HMPMA), the transition temperature (T _tr) decreased with increasing pressure, and the highest T _tr was observed at atmospheric pressure (0.1 MPa). For both polymers, the highest P _trs were observed at the lowest temperatures. The l polymer showed a specific negative peak in its CD spectrum at around 220 nm in the lower temperature region and the temperature dependence was reproduced by a single-step transition, with the midpoint corresponding to the T _tr obtained from the scattering measurements. Coupled with the results from the DSC, the different behavior between the P(l-HMPMA) and P(dl-HMPMA) could be explained in terms of the chain states before and after the transition. The cooperative factors derived from the DSC measurement revealed that about 4 to 5 polymers of the present size were necessary to perform a thermal transition for P(l-HMPMA), and that P(dl-HMPMA) underwent its transition as an almost single molecular event.This revised version was published online in June 2005 with correction to the article category.     

An Improved End-Point Fluorimetric Procedure for the Determination of Low Amounts of Trypsin Activity in Biological Samples Using Rhodamine-110-Based Substrates

A novel end-point fluorimetric procedure based on the use of rhodamine-110-labeled specific substrate was developed to determine trypsin activities in biological samples. We evaluated the ability of trichloroacetic acid and acetic acid to stop the enzymatic reaction without hindering the detection of the fluorescence of rhodamine-110 released into the reaction mixture from the specific substrate (CBZ-l-alanyl-l-arginine)₂-rhodamine-110. Trichloroacetic acid decreased markedly the fluorescence of rhodamine-110, even at low concentrations. On the other hand, the addition of 50 mmol/l acetic acid inactivated efficiently trypsin activity, causing minor effects on rhodamine-110 fluorescence. The proposed procedure was more sensitive than the spectrophotometric end-point method using N-α-benzoyl-dl-arginine-p-nitroanilide as substrate. The possibility of carrying out end-point fluorimetric assays improves the performance of monocell fluorimeters by setting specific conditions optimal for each enzyme activity independently of the fluorimeter. This method also allows replicate assays to be conducted simultaneously, resulting in considerable time saving and in increased performance of low-cost equipment.     

Mixed-ligand complexes of nickel(II) involving sulphur-containing ligands and diaminocarboxylic acids

Summary Stability constants for mixed-ligand complexes of the types [NiABH₂], [NiABH] and [NiAB] formed by Ni^II with l-cysteine (cys), d-penicillamine (pen) or l-cysteic acid (cya) as ligand A and dl-2,3-diaminopropionic acid (dapa), dl-2,4-diaminobutyric acid (daba) or dl-ornithine (orn) as ligand B have been determined by the computerbased analysis of pH titration data obtained at 37 °C and I = 0.15 mol dm^–3 (NaClO₄). In the [NiABH] species, for all three secondary ligands (B), when A = pen or cya the labile proton appears to be attached to the terminal amino group of ligand B, whereas when A = cys it is not clear where the proton is located. In all the systems in the [NiABH₂] species, one proton resides with the primary ligand (A) and the other with the secondary ligand (B). In the [NiAB]-type complexes, cys and pen chelate through the amino and thiolato groups, while cya binds in a glycine-like mode and the secondary ligands (B) coordinate in a terdentate manner.Author to whom all correspondence should be directed.     

Characterization of a Recombinant Thermostable Dehalogenase Isolated from the Hot Spring Thermophile <Emphasis Type="Italic">Sulfolobus tokodaii</Emphasis>

A putative dehalogenase, l-HAD_ST, from the thermophile Sulfolobus tokodaii, was cloned and expressed in Escherichia coli. The recombinant enzyme catalyzes the stereospecific dehalogenation of l-2-haloacids with similar levels of activity as its homolog from mesophiles. l-HAD_ST remains fully active after being incubated for 4 h at 70 °C and tolerates extreme pH conditions ranging from 4 to 10. Furthermore, it can be purified conveniently without the usage of any chromatography method. The high expression yield and easy purification procedure make the recombinant dehalogenase an excellent candidate for biotechnological applications.     

Magnetite Nanoparticles Immobilized Pectinase: Preparation,Characterization and Application for the Fruit Juices Clarification

In this work, pectinase was immobilized on the surface of silica‐coated magnetite nanoparticles via covalent attachment. The magnetite‐immobilized enzyme was characterized by Fourier transform infrared spectroscopy, X‐ray powder diffraction, scanning electron microscopy and vibrating sample magnetometery techniques. Response Surface Methodology using Minitab Software was applied for statistical designing of operating conditions in order to immobilize pectinase on magnetic nanoparticles. The optimal conditions were obtained at 30 °C and pH 5.5 with 42.97 μl pectinase for 2 h. The immobilization yield was 50.6% at optimized conditions. Compared to the free pectinase, the immobilized pectinase was found to exhibit enhanced enzyme activity, better tolerance to the variation of pH and temperature, and improved storage stability. Both free and immobilized samples reduced the viscosity of apple juice from 1.12 to 0.88 and 0.92 mm²s^?1, respectively, after 30 min at their optimum temperature. Furthermore, the immobilized enzyme could be reused six consecutive cycles and the efficiency loss in viscosity reduction was found to be only 8.16%.     

Reaction of hydroxyl radicals with S-nitrosothiols: Formation of thiyl radical (RS?) as the intermediate

The decomposition studies of S-nitrosothiols (RSNO) are important due to their potential role in vivo in connection with the storage and transport of nitric oxide (^•NO) within the body. Reactions of hydroxyl radicals (^•OH) with a number of RSNOs (S-nitroso derivatives of N-acetyl-dl-penicillamine, l-cysteinemethylester, N-acetylcysteamine, and dl-penicillamine) in aqueous medium at neutral and acidic pH have been reported in the present study. Radiation chemical technique (steady state and pulse radiolysis) has been utilized for the determination of the reaction rate constants, the end product analyses, and the transient intermediate species. The rate constants for the reaction of ^•OH with the selected RSNOs were determined using a competition kinetic method with 2′-deoxy-d-ribose as the competitor. All the rate constants were found to be of the order of diffusion controlled (10¹⁰ M⁻¹ s⁻¹). The degradation yield of RSNOs was found to be quantitative (i.e., G(–RSNO) ≈ G(^•OH)) at neutral and acidic pH. The major products of decomposition were the respective disulfide (RSSR) and nitrite (NO₂ ⁻). A good material balance is also obtained between the degradation yield and the formation of the products (i.e., G(–RSNO) ≈ G(RSSR) + G(NO₂ ⁻)). The major transient intermediate was the thiyl radical (RS^•). Its intermediacy was confirmed by making use of the electron transfer reaction of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS²⁻) to RS^•, which results in the formation of ABTS^•− having a transient absorption spectrum with λ_max at 410 nm. Based on these results, a generalized reaction mechanism is deduced for the reaction of ^•OH with RSNO.     

Simultaneous purification and reversible immobilization of d-amino acid oxidase from Trigonopsis variabilis on a hydrophobic support

Purification and reversible immobilization of d-amino acid oxidase from Trigonopsis variabilis could be simultaneously accomplished by hydrophobic interaction on Phenyl Sepharose CL-4B in the presence of 50 mM pyrophosphate buffer (pH 8.5). The presence of a high salt concentration of 2M, which is generally required for the hydrophobic interactions, was not essential for the hydrophobic immobilization. The enzyme in free as well as immobilized form was optimally active between pH 7.0 and 9.0. The immobilized preparation could be reused in a batch process for the conversion of d-amino acids to α-keto acids. When the activity of the preparation dropped below practical limits, the gel could be regenerated by water wash and recharged with fresh crude extract from yeast.     

Chiral discrimination ofN-(dansyl)-dl-amino acids on human serum albumin stationary phase: Effect of a mobile phase modifier

Summary The effect of perchlorate anion as mobile phase modifier on the separation factor, α, forN-(dansyl)-dl-norvaline andN-(dansyl)-dl-tryptophan on a human serum albumin (HSA) column was studied by varying the concentration,c, of the chaotropic agent and the column temperatureT. Gibbs-Helmholtz parameters Δ(ΔH) and Δ(ΔS) between thed andl enantiomers were determined from linear van't Hoff plots of lnα against 1/T. Thermodynamic results indicated that the enhancement of the separation factor observed asc was increased was enthalpically controlled owing to stereoselective H-bonding interactions. Such behavior was used to optimize the chromatographic conditions for separation ofN-(dansyl)-amino acids on HSA.