scholarly journals Part of the phospho group of pyridoxal phosphate may titrate over the pH range 5-8 in aspartate aminotransferase

1991 ◽  
Vol 280 (3) ◽  
pp. 832-833
Author(s):  
H B F Dixon
Keyword(s):  
Aspartate Aminotransferase ◽  
Pyridoxal Phosphate ◽  
Ph Range

scholarly journals Effect of pH, ionic strength and univalent inorganic ions on the reconstitution of aspartate aminotransferase

1974 ◽  
Vol 137 (2) ◽  
pp. 199-203 ◽  
Author(s):  
Liliana Gianfreda ◽  
Gennaro Marino ◽  
Rosaria Palescandolo ◽  
Vincenzo Scardi
Keyword(s):  
Ionic Strength ◽  
Aspartate Aminotransferase ◽  
Pyridoxal Phosphate ◽  
Water Structure ◽  
Inorganic Ions ◽  
Halide Ions ◽  
Ph Change ◽  
Effect Of Ph ◽  
Ph Range ◽  
Ph Curve

1. The effect of pH change on the reconstitution of aspartate aminotransferase (EC 2.6.1.1), i.e. the reactivation of the apoenzyme with coenzyme (pyridoxal phosphate and pyridoxamine phosphate), was studied in the pH range 4.2–8.9 by using three buffer systems at concentrations ranging from 0.025 to 0.1m. 2. Although the profile of the reconstitution rate–pH curve in the range pH5.2–6.8 (covered by sodium cacodylate–HCl buffer) reflects the influence of the H+ concentration on the reconstitution process, the profile of the curve in the pH ranges 4.2–5.6 and 7.2–8.25 (covered respectively by sodium acetate–acetic acid and Tris–HCl buffers) appears to be influenced by the ionic strength of the buffer. 3. The reconstitution is also influenced by univalent inorganic ions such as halide ions and, to a lesser extent, alkali metal ions, which are known to alter the water structure.

A Class of Drugs that Inhibits Platelet Release and Aggregation by Apparent Interference with Anion Transport

1979 ◽  
Author(s):  
N.R. Shulman ◽  
H.B. Pollard ◽  
K. Tack-Goldman
Keyword(s):  
Pyridoxal Phosphate ◽  
Human Platelets ◽  
Anion Transport ◽  
Serotonin Release ◽  
Secretory Cells ◽  
Chloride Uptake ◽  
Potential Alternative ◽  
Osmotic Lysis ◽  
Platelet Release ◽  
Ph Range

The platelet release reaction is analogous to the process of exocytosis by which many other secretory cells release hormones or mediators from intracellular granules. Anion transport blocking (ATB) drugs Inhibit release of epinephrine from isolated chromaffin granules (CG) by blocking chloride uptake and preventing osmotic lysis. Studies on platelets analagous to those done on CG showed that increasing osmotic strength in the range 600-1000 m0sm progressively suppressed serotonin release to completion and that ATB drugs (viz, probenecid, SITS, pyridoxal phosphate and suramin) at mM concentrations completely inhibited release and aggregation of human platelets stimulated by thrombin, ADP, A23187, epinephrine or collagen. Sulfinpyrazone has the appropriate structure for anionic blocking, and may suppress platelet function as effectively by this mechanism as by cycloxy-genase inhibition. The ATB drugs acted apparently to prevent movement of OH- from the more alkaline medium into the relatively acidic granule, for platelet release was not inhibited by replacing anions with isethionate or sucrose, but was markedly dependent on OH- in the pH range 6 to 7.5 where inhibition by the ATB drugs was competitive with respect to OH-. Since the ATB compounds include some relatively nontoxic drugs in common use, and since their action on platelets differs markedly from that of aspirin, they should receive attention as potential alternative or auxiliary antithrombotic agents.

The C-S lysis of L-cysteine conjugates by aspartate and alanine aminotransferase enzymes

1995 ◽  
Vol 14 (5) ◽  
pp. 422-427 ◽  
Author(s):  
Peter J Gaskin ◽  
Harriet J Adcock ◽  
Lorraine D Buckberry ◽  
Paul H Teesdale-Spittle ◽  
P Nicholas Shawl
Keyword(s):  
Aspartate Aminotransferase ◽  
Alanine Aminotransferase ◽  
Pyridoxal Phosphate ◽  
Enzyme Inhibitor ◽  
Potential Interaction ◽  
Direct Inhibition ◽  
Porcine Heart ◽  
Lyase Activity ◽  
Oxyacetic Acid ◽  
Dependent Mechanism

One biotransformation pathway which is responsible for the generation of mutagenic and cytotoxic metabolites is that of the C-S lysis (CSL) of L-cysteine conjugates. Thirteen cysteine S-conjugates, synthesised in our labora tories, were incubated with porcine heart aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT), and the C-S lyase activity for each enzyme-sub strate combination was determined. ASAT and ALAT were shown to exhibit CSL activity. It was also demonstrated that this activity was inhibited in the presence of the pyri doxal phosphate (PLP)-dependent enzyme inhibitor amino(oxyacetic acid) (AOAA) confirming the pyridoxal phosphate dependent mechanism by which C-S lysis is known to take place. Since the activities of these enzymes are used as biomarkers for the assessment of organ dam age, the potential interaction of L-cysteine conjugates with them may suppress their activity through direct inhibition.

scholarly journals N-(5′-Phosphopyridoxyl)glutamic acid and N-(5′-phosphopyridoxyl)-2-oxopyrrolidine-5-carboxylic acid and their action on the apoenzyme of aspartate aminotransferase

1971 ◽  
Vol 124 (1) ◽  
pp. 99-106 ◽  
Author(s):  
R M. Khomutov ◽  
H B. F. Dixon ◽  
L V. Vdovina ◽  
M P. Kirpichnikov ◽  
Y V. Morozov ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Carboxylic Acid ◽  
Glutamic Acid ◽  
Aspartate Aminotransferase ◽  
Fluorescence Spectra ◽  
Pyridoxal Phosphate ◽  
Hydroxyl Group ◽  
Side Chain ◽  
Compound I ◽  
Compound Ii

1. N-(5′-Phosphopyridoxyl)-l-glutamic acid (P-Pxy-Glu, compound I) is readily converted at pH3 into a substance (P-Pxy-Glp, compound II) characterized as N-(5′-phosphopyridoxyl)-2-oxopyrrolidine-5-carboxylic acid. 2. The u.v., i.r. and fluorescence spectra of P-Pxy-Glu and P-Pxy-Glp have been determined; from the u.v. spectra their pK values have been found and compared. 3. The apoenzyme of aspartate aminotransferase is rapidly and irreversibly inactivated by P-Pxy-Glu, but is inactivated more slowly by P-Pxy-Glp. The complex with P-Pxy-Glp is stable enough to be isolated, but it is slowly reactivated in the presence of excess of pyridoxal phosphate. 4. The u.v. spectrum of the complex of apoenzyme and P-Pxy-Glp suggests that it contains a hydrogen bond between the phenolic hydroxyl group and the pyrrolidone nitrogen; this specifies the conformation of most of the molecule of P-Pxy-Glp. This conformation is similar to that previously postulated for the enzyme–glutamate complex except for the side chain of glutamate. Hence both the affinity of P-Pxy-Glp for the apoenzyme and the fact that it is more easily removed than P-Pxy-Glu are explicable.

Evaluation of the IFCC-recommended procedure for serum aspartate aminotransferase as modified for use with the centrifugal analyzer.

1981 ◽  
Vol 27 (1) ◽  
pp. 156-159 ◽  
Author(s):  
D E Bruns ◽  
J Savory ◽  
A C Titheradge ◽  
R E Cross ◽  
M R Wills
Keyword(s):  
Cardiac Disease ◽  
Aspartate Aminotransferase ◽  
Present Method ◽  
Pyridoxal Phosphate ◽  
Extensive Evaluation ◽  
Serum Aspartate Aminotransferase

Abstract The IFCC-recommended procedure for aspartate aminotransferase (EC 2.6.1.1) was adapted to the centrifugal analyzer and evaluated during five years. The main hindrance to widespread use of the recommended method is the need for pre-incubation with pyridoxal phosphate. The present method includes a 10-min pre-incubation with pyridoxal phosphate. Extensive evaluation of the method with and without this pre-incubation confirms earlier reports that it eliminates some significant errors, especially for samples from patients with cardiac disease. However, the pre-incubation can be briefer than the recommended 10 min and still provide acceptable results.

Effects of Buffers on Aspartate Aminotransferase Activity and Association of the Enzyme with Pyridoxal Phosphate

1975 ◽  
Vol 21 (11) ◽  
pp. 1585-1591 ◽  
Author(s):  
Robert Rej ◽  
Raymond E Vanderlinde
Keyword(s):  
Schiff Base ◽  
Aspartate Aminotransferase ◽  
Phosphate Buffer ◽  
Pyridoxal Phosphate ◽  
Human Origin ◽  
Aminotransferase Activity ◽  
Factors Influencing ◽  
Absorbance Spectra ◽  
Stimulation Of

Abstract Using purified enzymes of human origin and patients’ sera, we examined factors influencing the in vitro association of pyridoxal phosphate with aspartate aminotransferase (EC 2.6.1.1). The rate of association was markedly retarded by phosphate buffer in comparison with tris(hydroxymethyl)aminomethane or six other buffers. Pyridoxal phosphate at an incubation concentration of 130 µmol/liter reactivated the entire apoenzyme portion of an apoenzyme/holoenzyme mixture within 5 min in tris(hydroxymethyl)aminomethane; in contrast, less than 20% was associated during 15 min in phosphate. Activity measured in tris(hydroxymethyl)aminomethane-buffer without exogenous pyridoxal phosphate was 4% greater than that in phosphate and was slightly increased by increasing the pH of the assay mixture from 7.5 to 8.0. Aspartate in the incubation medium did not retard the stimulation in tris(hydroxymethyl)aminomethane buffer. While the magnitude of stimulation varied greatly among sera, a consistent mean stimulation of 30% for groups of sera with normal activities was found when asparate at 125 mmol/liter, 2-oxoglutarate at 6.7 mmol/liter and tris(hydroxymethyl)aminomethane at 90 mmol/liter were used, an increase over the 16% with phosphate buffer [Clin. Chem. 19, 92 (1973)]. Absorbance spectra suggest pyridoxal phosphate exists as the Schiff base of tris(hydroxymethyl)aminomethane or aspartate, or both, under conditions of assay incubation (without addition of 2-oxoglutarate). Nonenzymatic catalysis of the reaction by pyridoxal phosphate alone or a formation of a protein/pyridoxal phosphate adduct was discounted with use of D-asparate substrates

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