Quantitation of movement of the phosphoryl group during catalytic transfer in the arginine kinase reaction: 31P relaxation measurements on enzyme-bound equilibrium mixtures |
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Authors: | Ray Bruce D Jarori Gotam K Rao B D Nageswara |
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Institution: | (1) Department of Physics, Indiana University, Purdue University at Indianapolis (IUPUI), 402 N. Blackford Street, Indianapolis, IN, 46202-3273, U.S.A;(2) Present address: Tata Institute of Fundamental Research, Mumbai, India |
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Abstract: | 31P nuclear spin relaxation measurements have been made on enzyme-bound equilibrium mixtures of lobster-muscle arginine kinase in the presence of substituent activating paramagnetic cation Co(II) (in place of Mg(II)), i.e., on samples in which the reaction, ECoATParginine ECoADPP-arginine, is in progress. The results have been analyzed on the basis of a previously published theory (Nageswara Rao, B.D. (1995) J. Magn. Reson., B108, 289–293) to determine the structural changes in the reaction complex accompanying phosphoryl transfer. The analysis enables the determination of the change in the Co(II)-31P (-P(ATP)) vector as the transferable phosphoryl group moves over and attaches to arginine to form P-arginine. It is shown that the Co(II)-31P distance of 3.0 Å, representing direct coordination of Co(II) to -P(ATP), changes to 4.0 Å when P-arginine is formed in the enzyme-bound reaction complex. This elongation of the Co(II)-31P vector implies an excursion of at least 1.0 Å for the itinerant phosphoryl group on the surface of the enzyme. |
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Keywords: | arginine kinase catalytic transfer phosphoryl group movement 31P relaxation |
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