NATURE OF ANION INHIBITION OF HUMAN RED-CELL CARBONIC-ANHYDRASES

被引:68
作者
MAREN, TH
COUTO, EO
机构
[1] Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville
基金
美国国家卫生研究院;
关键词
D O I
10.1016/0003-9861(79)90302-3
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
We studied anionic inhibition of the reaction CO2 + OH-⇄ HCO3- catalyzed by human red cell carbonic anhydrase B (I) and C (II), using iodide and cyanate. In the forward reaction with respect to CO2 as the substrate, inhibition was mixed but favoring noncompetitive; the back reaction, with HCO3- as the substrate, yielded strict competitive kinetics. Mean inhibition constants, KI, in the pH range 7.2-7.5 are: iodide, 0.5 mm for enzyme B and 16 mm for C; cyanate, 0.8 μm for B and 20 μm for C. When OH- was considered as the substrate for the forward reaction, cyanate and chloride behaved as competitive inhibitors. The true inhibition constant (KI0) for cyanate (calculated for infinitely low OH-) is 0.4 μm for enzyme B and 4 μm for C. Apart from the difference in anion affinity and some 10-fold higher activity of C > B, the isozymes showed similar patterns of inhibition. Data agree with generally proposed mechanisms describing the active site as ZnH2O with pKa of about 7. © 1979.
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页码:501 / 510
页数:10
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