Edwards S L, Mauro J M, Fishel L A, Wang J M, Miller M A, Xuong N H, Kraut J
Department of Chemistry, University of California, San Diego, La Jolla.
Prog Clin Biol Res. 1988;274:463-75.
A difference Fourier map shows small structural perturbations on oxidation of cytochrome c peroxidase (CCP) to its semi-stable intermediate, compound I. Least-squares refinement of both CCP and compound I quantifies these perturbations and suggests that the radical site may be on the distal side of the heme, since that is where most of the small movements occur. Several engineered mutants of CCP were created in an attempt to assess the function of various side chains, among them Trp-51----Phe, Trp-191----Phe and His-181----Gly. X-ray structures of the mutant CCP's confirm that only minimal changes are caused by these substitutions. Preliminary examination of the mutants' kinetic properties show that Trp-51 is not the radical site; that Trp-191 has an important enzymic function; and that His-181 is not essential for electron transfer, but probably has some more indirect role. The locus of the radical in compound I, however, remains to be established.
差分傅里叶图显示，细胞色素c过氧化物酶（CCP）氧化为其半稳定中间体化合物I时存在微小的结构扰动。对CCP和化合物I进行最小二乘精修可量化这些扰动，并表明自由基位点可能位于血红素的远端，因为大多数微小移动都发生在那里。为了评估各种侧链的功能，构建了几个CCP的工程突变体，其中包括色氨酸-51突变为苯丙氨酸、色氨酸-191突变为苯丙氨酸以及组氨酸-181突变为甘氨酸。突变体CCP的X射线结构证实，这些取代仅引起最小的变化。对突变体动力学性质的初步研究表明，色氨酸-51不是自由基位点；色氨酸-191具有重要的酶功能；组氨酸-181对电子转移不是必需的，但可能具有一些更间接的作用。然而，化合物I中自由基的位置仍有待确定。
