Badger M R, Andrews T J, Canvin D T, Lorimer G H
J Biol Chem. 1980 Aug 25;255(16):7870-5.
Hydrogen peroxide inhibited both carboxylase and oxygenase activities of purified, and fully activated, spinach ribulose-1,5-bisphosphate (RuP2) carboxylase-oxygenase. Inhibition of the carboxylase reaction was mixed competitive with respect to CO2 (Ki = 1.2 mM) and uncompetitive with respect to RuP2. For the oxygenase reaction, H2O2 was a competitive inhibitor with respect to O2 (Ki = 2.1 mM) and an uncompetitive inhibitor with respect to RuP2. H2O2 did not alter the stoichiometry between CO2 and RuP2 in the carboxylase reaction, indicating that H2O2 was not itself a substrate for the enzyme. RuP2 decreased the rate of deactivation of the enzyme which occurred at limiting CO2 concentrations. H2O2 greatly enhanced this stabilizing effect of RuP2 but had no effect on the rate of deactivation in the absence of RuP2. The inhibitory and stabilizing effects of H2O2 varied similarly with H2O2 concentration. These instantaneous, reversible effects of H2O2 were readily distinguishable from an irreversible inhibitory effect which occurred quite slowly, and in the absence of RuP2. These observations are discussed in relation to the enzyme's catalytic mechanism and its activation-deactivation transformations.
过氧化氢抑制了纯化且完全活化的菠菜核酮糖-1,5-二磷酸羧化酶加氧酶（RuP2羧化酶加氧酶）的羧化酶和加氧酶活性。羧化酶反应的抑制作用对于二氧化碳而言是混合型竞争性抑制（Ki = 1.2 mM），对于RuP2而言是非竞争性抑制。对于加氧酶反应，H2O2对于氧气而言是竞争性抑制剂（Ki = 2.1 mM），对于RuP2而言是非竞争性抑制剂。H2O2并未改变羧化酶反应中二氧化碳与RuP2之间的化学计量关系，这表明H2O2本身并非该酶的底物。RuP2降低了在二氧化碳浓度受限情况下发生的酶失活速率。H2O2极大地增强了RuP2的这种稳定作用，但在不存在RuP2时对失活速率没有影响。H2O2的抑制作用和稳定作用随H2O2浓度的变化情况相似。H2O2的这些瞬时、可逆效应很容易与在不存在RuP2时相当缓慢发生的不可逆抑制效应区分开来。结合该酶的催化机制及其活化-失活转变对这些观察结果进行了讨论。
