Catalytic versatility of angiotensin converting enzyme: catalysis of an .alpha.,.beta.-elimination reaction

1984 ◽  
Vol 106 (21) ◽  
pp. 6440-6442 ◽  
Author(s):  
Thomas E. Spratt ◽  
E. T. Kaiser
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Enzyme Catalysis ◽  
Converting Enzyme ◽  
Elimination Reaction ◽  
Beta Elimination ◽  
Alpha Beta

scholarly journals Purification and characterization of human hepatic cysteine-conjugate β-lyase

1986 ◽  
Vol 235 (2) ◽  
pp. 569-575 ◽  
Author(s):  
H Tomisawa ◽  
S Ichihara ◽  
H Fukazawa ◽  
N Ichimoto ◽  
M Tateishi ◽  
...  
Keyword(s):  
Human Liver ◽  
Gel Filtration ◽  
Deae Cellulose ◽  
Elimination Reaction ◽  
Purification And Characterization ◽  
Ph Optimum ◽  
Beta Elimination ◽  
Alpha Beta ◽  
Hydroxyapatite Gel

Cysteine-conjugate beta-lyase (EC 4.4.1.13) was purified about 880-fold from human liver obtained post mortem. The purification procedure included (NH4)2SO4 precipitation, chromatography on DEAE-cellulose and hydroxyapatite, gel filtration on Sephadex G-200, and chromatofocusing. The purified enzyme cleaves the C-S bond of several S-aryl-L-cysteines to yield equimolar amounts of thiols, pyruvic acid and ammonia via an alpha beta-elimination reaction. The Mr of the enzyme was estimated to be 88,000 by gel filtration. The enzyme is thermolabile, has a pH optimum of 8.5, and an apparent Km of 0.7 mM towards S-(p-bromophenyl)-L-cysteine. The enzyme requires pyridoxal 5′-phosphate as a cofactor, and hence the enzyme activity was completely abolished by hydroxylamine. No effect of EDTA or thiol-blocking reagents was observed on the activity of the enzyme.

Kinetics of pulmonary angiotensin-converting enzyme and 5'-nucleotidase in vivo

1984 ◽  
Vol 57 (4) ◽  
pp. 1173-1181 ◽  
Author(s):  
J. D. Catravas ◽  
R. E. White
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Enzyme Inhibitor ◽  
Competitive Inhibitor ◽  
Converting Enzyme ◽  
Microvascular Endothelium ◽  
Vasoactive Substances ◽  
Alpha Beta ◽  
Kinetics Of

Angiotensin-converting enzyme and 5′-nucleotidase line the luminal surface of pulmonary microvascular endothelium and participate in the synthesis and/or degradation of potent vasoactive substances. We applied Michaelis-Menten kinetics in simultaneous estimations of apparent constants Km and Amax (product of Vmax and microvascular plasma volume) of these two enzymes for the substrates 3H-labeled benzoyl-Phe-Ala-Pro and 14C-labeled 5′AMP, respectively, in vivo. Values of angiotensin-converting enzyme for benzoyl-Phe-Ala-Pro (Km = 10–11 microM; Amax = 12–13 mumol X min-1) were somewhat higher than published estimates in vitro and changed predictably in response to the known enzyme inhibitor captopril. Kinetic values of 5′nucleotidase for 5′AMP (Km = 3–4 microM; Amax = 3–4 mumol/min) were substantially lower than those reported in vitro but also responded predictably to the competitive inhibitor of 5′nucleotidase, adenosine 5′[alpha, beta-methylene]diphosphate. These data offer in vivo estimates of enzyme kinetics that are useful in revealing enzyme behavior in their normal physiological environment and provide means of evaluating the action of pharmacological, physiological, and pathological modulators of enzyme activity, in vivo.

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