STUDIES ON MECHANISM OF INHIBITION OF REDOX ENZYMES BY SUBSTITUTED HYDROXAMIC ACIDS
STUDIES ON MECHANISM OF INHIBITION OF REDOX ENZYMES BY SUBSTITUTED HYDROXAMIC ACIDS
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DOI：
10.1016/0005-2744(78)90227-9
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发表时间：
1978-01-01
期刊：
影响因子：
--
通讯作者：
BONNER, WD
中科院分区：
文献类型：
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作者：
RICH, PR;WIEGAND, NK;BONNER, WD
发现取代的伯羟肟酸对许多氧化还原酶的催化活性有抑制作用。这种抑制与酶的金属活性部位的性质无关，也与含氧底物的性质无关。选择了两种易被异羟肟酸抑制的蘑菇酪氨酸酶(单酚、二羟基苯丙氨酸：氧氧化还原酶，EC 1.14.18.1)和辣根过氧化物酶(供体：过氧化氢氧化还原酶，EC 1.11.1.7)进行了较为详细的研究。对部分纯化的双孢菇酪氨酸酶抑制作用的动力学分析表明，对底物浓度的抑制是可逆的，对底物浓度的抑制是竞争性的，而对分子氧浓度的抑制不是竞争性的。用分光光度和电子顺磁共振研究了水杨基异羟肟酸与辣根过氧化物酶的结合，结果表明该异羟肟酸与辣根过氧化物酶的结合方式与典型底物对苯二酚的结合方式相同。结合反应的光谱和热力学测量表明，这个结合位置靠近酶的血红素基团，但不是直接在酶的血红素基团上。显然，异羟肟酸的抑制模式不需要像通常认为的那样是通过金属络合来实现的，而涉及还原底物结合部位的氢键或异羟肟酸与酶中接受电子的基团之间形成电荷转移络合物的机制被认为是更可行的。讨论了这些发现与对其他异羟肟酸抑制体系性质的推论的相关性。
Substituted primary hydroxamic acids were found to inhibit the catalytic activity of a number of redox enzymes. The inhibition was not related to the nature of the metal-active site of the enzyme nor to the nature of the oxygen-containing substrate. Two easily available enzymes, mushroom tyrosinase (monophenol,dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) and horseradish peroxidase (donor:hydrogen-peroxide oxidoreductase, EC 1.11.1.7), which were potently inhibited by hydroxamic acids, were chosen for more detailed study. A kinetic analysis of the inhibitory effects on the partially purified tyrosinase of mushroom (Agaricus bispora) revealed that inhibition was reversible and competitive with respect to reducing substrate concentration, but was not competitive with respect to molecular oxygen concentration. A spectrophotometric and EPR study of the binding of salicylhydroxamic acid to horseradish peroxidase revealed that this hydroxamic acid was bound to the enzyme in the same manner as a typical substrate, hydroquinone. Spectroscopic and thermodynamic measurements of the binding reactions suggested that this binding site is close to, but not directly onto, the heme group of the enzyme. Apparently the mode of inhibition of hydroxamic acids need not be, as generally supposed, by metal chelation, and mechanisms involving either H-bonding at the reducing substrate binding site or the formation of a charge transfer complex between hydroxamic acid and an electron-accepting group in the enzyme are considered to be more feasible. The relevance of these findings to deductions on the nature of other hydroxamic acid-inhibitable systems is discussed.