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首页> 美国卫生研究院文献>other >Effect of Alternative Distal Residues on the Reactivity of Cytochrome c Peroxidase: Properties of CcP Mutants H52D H52E H52N and H52Q
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Effect of Alternative Distal Residues on the Reactivity of Cytochrome c Peroxidase: Properties of CcP Mutants H52D H52E H52N and H52Q

机译：替代远端残留对细胞色素C过氧化物酶反应性的影响：CCP突变体H52DH52EH52N和H52Q的性质

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摘要

To test the effect of alternative bases at the distal histidine position, four CcP variants have been constructed that substitute the two basic residues, aspartate and glutamate, and their amides, asparagine and glutamine, for histidine-52, i.e., CcP(H52D), CcP(H52E), CcP(H52N), and CcP(H52Q). All four mutants catalyze oxidation of ferrocytochrome c by H2O2 with steady-state activities that are between 250 and 7,700 times slower than wild-type CcP at pH 6.0, 0.10 M ionic strength, 25 °C. The rate of Compound I formation is decreased between 3.5 and 5.4 orders of magnitude for the mutants compared to wild-type CcP, with the rate of the reaction between CcP(H52Q) and H2O2 the slowest yet observed for any CcP mutant. A correlation between the rate of Compound I formation and the rate of HCN binding for CcP and various CcP distal pocket mutants provides strong evidence that the rate-limiting step in CcP Compound I formation is deprotonation of H2O2 within the distal heme pocket under the experimental conditions employed in this study. While CcP(H52E) reacts stoichiometrically with H2O2 to form Compound I, only ~36% of CcP(H52D), ~21% of CcP(H52Q) and ~8% of CcP(H52N) appear to be converted to Compound I during their respective reactions with H2O2. This is partially due to the slow rate of Compound I formation and the rapid endogenous decay of Compound I for these mutants. The pathways for the endogenous decay of Compound I for the four mutants used in this study are distinct from that of wild-type CcP Compound I.

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