Rate-Limiting Domain and Loop Motions in Arginine Kinase

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• 作者：Omar Davulcu ; Jack J. Skalicky ; Michael S. Chapman
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：May 17, 2011
• 年：2011
• 卷：50
• 期：19
• 页码：4011-4018
• 全文大小：904K
• 年卷期：v.50,no.19(May 17, 2011)
• ISSN：1520-4995

文摘

Arginine kinase catalyzes the reversible transfer of a phosphoryl group between ATP and arginine. It is the arthropod homologue of creatine kinase, buffering cellular ATP levels. Crystal structures of arginine kinase, in substrate-free and substrate-bound forms, have revealed large conformational changes associated with the catalytic cycle. Recent nuclear magnetic resonance identified movements of the N-terminal domain and a loop comprising residues I182鈭扜209 with conformational exchange rates in the substrate-free enzyme similar to the turnover rate. Here, to understand whether these motions might be rate-limiting, we determined activation barriers for both the intrinsic dynamics and enzyme turnover using measurements over a temperature range of 15鈭?0 掳C. <sup>15sup>N transverse relaxation dispersion yields activation barriers of 46 卤 8 and 34 卤 12 kJ/mol for the N-terminal domain and I182鈭扜209 loop, respectively. An activation barrier of 34 卤 13 kJ/mol was obtained for enzyme turnover from steady-state kinetics. The similarity between the activation barriers is indeed consistent with turnover being limited by backbone conformational dynamics and pinpoints the locations of potentially rate-limiting motions.