Radiation-induced inactivation of angiotensin-converting enzyme in solutions

Radiation-induced inactivation of angiotensin-converting enzyme (ACE) in the low-dose range is characterized by the existence of a concentration- and pH-dependent induction period, activation, and inactivation. These effects are probably related to the change in the conformational flexibility of the active center in conjunction with the retention of the autoprotective multistep mechanism of the protection of the entire molecule. The schemes of radiation-induced reactions occurring in ACE are presented. The radiation-chemical yield of inactivation of ACE has a maximum at pH 7.5 independent of the initial concentration of the enzyme, which allows inference of a conformational transition in this pH range.For Part l, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 223–229, January, 1996.     

A theoretical study of angiotensin-converting enzyme inhibitors

Summary INDO molecular orbital calculations are reported for 35 selected angiotensin-converting enzyme inhibitors. QSARs are developed between pI₅₀ data and molecular electronic indices. The QSARs obtained reflect the importance of both charge-charge interactions between inhibitor and receptor and of specific interactions between groups on the inhibitor with points around the molecule which are postulated to correspond to binding sites at the receptor.     

Radiation-induced inactivation of angiotensin-converting enzyme in aqueous solutions

Radiation-induced inactivation of angiotensin-converting enzyme (ACE) was studied. The relationship of this process to damage to aromatic amino acid residues (tyrosine and tryptophan) was demonstrated by the method of second derivatives of UV spectra. In some cases, the dependence of inactivation on dose had an induction period. The comparison of the radiation-induced inactivation parameters of ACE, serine proteinases, and horseradish peroxidase points to a significant stabilizing effect of carbohydrate residues in glycoproteins (autoprotective mechanism). At pH 7.5, conformational changes occur in ACE. Low accessibility of the active center of this enzyme was suggested.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1322–1325, July, 1994.     

Radiation-induced inactivation of the angiotensin-converting enzyme in solutions

The effect of NaCl concentration (0–0.15 mol L⁻¹) and γ-irradiation dose on the catalytic activity of the angiotensin-converting enzyme is considered. Special regions in which a particular mechanism of dose response predominates are identified. In acid and alkaline media, there are regions of substantial enzymic activation; in addition, damped oscillations of the enzymic activity are observed. At pH 7.5, when the enzyme adopts a more “unfolded” conformation, the clearly defined activation peaks on the surface relief are smoothed over, indicating a decrease in the effect of the salt concentration. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2359–2363, December, 1999.     

Some aspects of the angiotensin-converting enzyme for leukemias

Russian Chemical Bulletin - The present article shows the diagnosis of different type leukemias in children by the activity of angiotensin-converting enzyme in blood serum to be not promising....     

Preparative isolation of angiotensin-converting enzyme from human lung.

Angiotensin-converting enzyme from human lung was purified to apparent homogeneity using a five-step purification procedure consisting of ammonium sulfate precipitation, ion-exchange chromatography on DEAE Sephadex A-50, gel permeation on Sephadex G-200, chromatofocusing on a polybuffer exchange (PBE 94) column and high-performance liquid chromatographic gel permeation on a Bio-Sil TSK-250 column. This procedure gave an approximately 700-fold purification with a 20% yield compared to a 550-fold purification and a 1% yield with an affinity chromatography-based procedure. The 20-fold greater yield of the five-step procedure offers a major advantage for preparative use in the structural characterization of angiotensin-converting enzyme.     

Production of 67Cu via the 68Zn(p,2p)67Cu reaction and recovery of 68Zn target

The radionuclide ⁶⁷Cu was produced via the ⁶⁸Zn(p,2p)⁶⁷Cu reaction by irradiating enriched ⁶⁸Zn targets with 70 MeV proton beam. Copper-67 was chemically separated from the zinc target by ion-exchange chromatography using Chelex-100 chelating ion-exchange resin. Procedure for recovery of the enriched ⁶⁸Zn was developed. The target recovery yield of this method was evaluated to be more than 97%.     

Pyrrolidine derivatives — Inhibitors of angiotensin-converting enzyme (review)

Methods for the synthesis and the compositions and biological activities of pyrrolidine derivatives that are inhibitors of angiotensin-converting enzyme are discussed. The most active inhibitors are 1-(D-3-mercapto-2-methylpropanoyl)-L-proline (captropril), dehydroproline derivatives, and phosphorus-, zinc-, and germanium-containing derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1443–1454, November, 1984.     

Activity of angiotensin-converting enzyme inhibitors in venoms of central Asian snakes

The inhibition of angiotensin-converting enzyme (ACE, K.F.3.4.15.1) by low-molecular-weight fractions of venoms from central Asian snakes was studied using N-(3-[2-furyl]acryloyl)-Phe-Gly-Gly (FAPGG) as substrate. Their activity is substantial in peptide fractions of poisons from snakes of the Viperidae and Crotalidae families and completely absent in cobra poison (Elapidae).Institute of Biochemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (99871) 162 32 56. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 254–256, May–June, 2000.     

Determination in plasma of angiotensin-converting enzyme inhibitor by inhibitor-binding assay.

A method of determining a new angiotensin-converting enzyme inhibitor (CS-622) and its active metabolite (RS-5139) in plasma by inhibitor-binding assay has been developed using high-performance liquid chromatography. The assay is based on the principle that the amount of inhibitor bound to the enzyme is inversely related to the amount of hippuric acid liberated on hydrolysis from the artificial substrate (hippuryl-L-histidyl-L-leucine). Plasma was heated at 60 degrees C for 15 min, to inactivate endogenous enzyme, and preincubated with rabbit-lung angiotensin-converting enzyme at 37 degrees C for 3 min. The artificial substrate (5.75 mg/ml in pH 8.3 phosphate buffer containing sodium chloride) was added to the resulting solution, and the mixture was incubated for 30 min. The reaction was terminated by the addition of 2 M hydrochloric acid. The hippuric acid liberated on hydrolysis was extracted with ethyl acetate and determined by reversed-phase chromatography using methylparaben as an internal standard. The total concentration of the inhibitor and its metabolite were determined by this method after de-esterification by rat-plasma esterase. The standard curve was obtained by the regression analysis of log concentration against logit response. The within-day and day-to-day precision were satisfactory. The proposed method is simple, rapid and sensitive enough to determine angiotensin-converting enzyme inhibitor in plasma.     

Mass spectral fragmentation reactions of angiotensin-converting enzyme (ACE) inhibitors

A variety of mass spectrometric techniques have been employed in the study of a series of structurally similar compounds used in the treatment of hypertension. The compounds, known collectively as angiotensin-converting enzyme (ACE) inhibitors, all share the amino acid residue proline or some variant thereof, as a common structural element. The gas phase fragmentation behavior of these compounds has been explored systematically using various instruments and techniques. An interesting dissociation process (rearrangement) unique to one of the compounds, lisinopril, has been investigated using isotopic labeling experiments and exact mass measurements. The general nature of the process has been probed through both the positive and negative ion analyses of fourteen related compounds exhibiting structural homology.     

Optimization of capillary electrophoretic separation of several inhibitors of the angiotensin-converting enzyme

Capillary electrophoretic separation of eight inhibitors of the angiotensin-converting enzyme, viz., enalapril, lisinopril, quinapril, fosinopril, perindopril, ramipril, benazepril and cilazapril, was investigated with respect to the following parameters: pH of the running buffer, organic modifiers and surfactants. The most critical parameter is the pH of the running buffer. The addition of sodium dodecyl sulfate had a negative influence on the peak symmetry, and selectivity was not improved. The separation of the eight compounds can be performed by means of two phosphate buffers (each 100 mM) at pH 7.0 and pH 6.25, respectively. This combination is necessary for the selective identification of structurally related substances because of their similar pKa values.     

Conformational fingerprinting of angiotensin-converting enzyme in the blood in health and disease

The binding pattern of the set of 16 monoclonal antibodies to the different epitopes on the surface of two domains of angiotensin-converting enzyme, i.e., conformational fingerprinting, allows to reveal in blood the presence of an enzyme that is not produced by lung endothelial cells, but rather by other cells, e.g., Gaucher’s cells and sarcoid granuloma cells. The existence of angiotensin-converting enzyme with changed conformation in the blood of patients with uremia has been shown; this enzyme was characterized by enhanced activity towards angiotensin I and decreased ability to be inhibited by specific inhibitors. The prospects of discovering conformationally changed enzyme in blood of patients with atrial fibrillation have also been discussed.     

In vivo behavior of carboxymethylcellulose based microgels containing 67Cu

Using a mouse model, an organ distribution for microgels of carboxymethyl cellulose cross-linked with ⁶⁷Cu²⁺ ions was investigated and compared with the distribution of free ⁶⁷Cu²⁺ ions from ⁶⁷CuCl₂. The clearance of the microgels through both liver and kidneys was demonstrated. An additional examination of distribution for [³H]CMC microparticles and [³H]CMC–Cu microgels revealed no copper release from the microgels in vivo.     

Residue ionization in LpxC directly observed by 67Zn NMR spectroscopy

The pH dependence of the solid-state (67)Zn NMR lineshapes has been measured for both the wild type (WT) and the H265A mutant of Aquifex aeolicus LpxC, each in the absence of substrate (resting state). The (67)Zn NMR spectrum of WT LpxC at pH 6 (prepared at 0 degrees C) contains two overlapping quadrupole lineshapes with C q values of 10 and 12.9 MHz, while the spectrum measured for the sample prepared at a pH near 9 (at 0 degrees C) is dominated by the appearance of a third species with a C q of 14.3 MHz. These findings are consistent with the two p K a values previously observed by the bell-shaped dependence of the LpxC-catalyzed reaction. On the basis of comparison of the experimental results with predictions from quantum mechanical/molecular mechanical (QM/MM) modeling, we suggest that p K a1 (low pH) represents the ionization of Glu78 and p K a2 (high pH) reflects the ionization of another active site residue located near the zinc ion, such as His265. These results are also consistent with water being bound to the Zn (2+) ion throughout this pH range. The (67)Zn NMR spectra of the H265A mutant appear to be pH independent, with a C q of 9.55 MHz being sufficient to describe both low- and high-pH data. The QM/MM models of the H265A mutant suggest that over this pH range water is bound to the zinc ion while Glu78 is protonated.     

Simultaneous determination of hydrochlorothiazide and several inhibitors of angiotensin-converting enzyme by capillary electrophoresis

A capillary electrophoresis method was developed for the simultaneous determination of hydrochlorothiazide and several angiotensin-converting enzyme (ACE) inhibitors: enalapril, lisinopril, quinapril, fosinopril, ramipril, and cilazapril. The most critical parameter is the pH of the running buffer. Separation was performed on a fused-silica capillary (52 cm total length x 75 microm I.D.) using a sodium phosphate buffer (pH 7.25; 100 mM). The method was successfully applied to the quantitative determination of these compounds in their corresponding pharmaceutical formulation. The method was validated in terms of linearity of response, reproducibility and accuracy.