RELAXATION SPECTRA OF ADENOSINE TRIPHOSPHATE-CREATINE PHOSPHOTRANSFERASE

被引:58
作者
HAMMES, GG
HURST, JK
机构
[1] Department of Chemistry, Cornell University, Ithaca
关键词
D O I
10.1021/bi00831a040
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
A kinetic study of the reaction catalyzed by creatine kinase has been carried out, primarily using the temperature-jump method. The results obtained indicate that the binding of adenosine di- and triphosphates and their metal complexes with the divalent cations Mg2+, Ca2+, and Mn2+ is accompanied by a conformational change of the enzyme-substrate complex. The rates of this process are quite similar in all cases. No conformational changes have been detected with creatine and phosphocreatine binding. An isomerization (or conformational change) of the ternary complex (both nucleotide and creatine substrates bound) may also occur, but a definite interpretation is complicated by relaxation processes associated with metal-nucleotide interactions. Rate constants for the initial association- dissociation of adenosine diphosphate and the metal-adenosine triphosphate complexes with enzyme and the subsequent isomerization are reported, and limits on the corresponding constants for adenosine triphosphate and metal-adenosine triphosphate complexes are placed. At 11° the bimolecular rate constant for adenosine diphosphate association is 2.3 X 107 M-1 sec-1, while that for the metal-adenosine diphosphate complex is similar for all three metals, ranging from about 2-7 X 106 M-1 sec-1. In contrast for most metal-ligand associations, where dissociation of water molecules from the inner coordination sphere of the metal is rate limiting, the bimolecular rate constants associated with Mg2+, Ca2+, and Mn2+ vary several orders of magnitude. Mechanistic implications of the results are discussed. A model consistent with the data is one where the activator cation does not bridge between the enzyme and adenine nucleotide in the enzyme-substrate complex, and discrimination with respect to the metal activator occurs mainly in the rate-determining step. © 1969, American Chemical Society. All rights reserved.
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页码:1083 / &
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