Abstract
When ATP binds to myosin in the presence of Mg2+ there follows a rapid cleavage reaction to yield a myosin-product complex whose breakdown is rate-limiting in the overall adenosine triphosphatase reaction at 21 degrees and pH 8.0. Recent kinetic studies on this system have led to the proposal that the cleavage of ATP bound to myosin is reversible. This conclusion is based in part on the observation that when ATP is mixed with an excess of myosin active sites a small amount of tightly bound ATP exists whose life-time coincides with that of the myosin-product complex and implies these two species are in equilibrium during their decay. Previous oxygen exchange studies have shown that phosphate released as free product contains more than one oxygen atom from water. A rapid equilibration between myosin-bound ATP and a myosin-products complex can account for the extra water oxygen incorporation of the product phosphate. Such a model requires that the gamma-phosphoryl group of the bound ATP also exchanges its oxygen atoms with water. Results presented in this paper show that protein-bound ATP labeled in the three terminal oxygen atoms of the gamma-phosphoryl group with 18O exchanges about 75% of its label within 2 s of binding to the active site of myosin. This result provides chemical evidence for a model in which bound ATP undergoes a reversible reaction with water. Incomplete exchange may arise from kinetic and/or structural restraints on the mechanism and plausible models are discussed.
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Selected References
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- Bagshaw C. R., Eccleston J. F., Eckstein F., Goody R. S., Gutfreund H., Trentham D. R. The magnesium ion-dependent adenosine triphosphatase of myosin. Two-step processes of adenosine triphosphate association and adenosine diphosphate dissociation. Biochem J. 1974 Aug;141(2):351–364. doi: 10.1042/bj1410351. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bagshaw C. R., Trentham D. R. The characterization of myosin-product complexes and of product-release steps during the magnesium ion-dependent adenosine triphosphatase reaction. Biochem J. 1974 Aug;141(2):331–349. doi: 10.1042/bj1410331. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bagshaw C. R., Trentham D. R. The reversibility of adenosine triphosphate cleavage by myosin. Biochem J. 1973 Jun;133(2):323–328. doi: 10.1042/bj1330323. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Boyer P. D., Cross R. L., Momsen W. A new concept for energy coupling in oxidative phosphorylation based on a molecular explanation of the oxygen exchange reactions. Proc Natl Acad Sci U S A. 1973 Oct;70(10):2837–2839. doi: 10.1073/pnas.70.10.2837. [DOI] [PMC free article] [PubMed] [Google Scholar]
- LEVY H. M., KOSHLAND D. E., Jr Mechanism of hydrolysis of adenosinetriphosphate by muscle proteins and its relation to muscular contraction. J Biol Chem. 1959 May;234(5):1102–1107. [PubMed] [Google Scholar]
- Lymn R. W., Taylor E. W. Transient state phosphate production in the hydrolysis of nucleoside triphosphates by myosin. Biochemistry. 1970 Jul 21;9(15):2975–2983. doi: 10.1021/bi00817a007. [DOI] [PubMed] [Google Scholar]
- Mannherz H. G., Schenck H., Goody R. S. Synthesis of ATP from ADP and inorganic phosphate at the myosin-subfragment 1 active site. Eur J Biochem. 1974 Oct 1;48(1):287–295. doi: 10.1111/j.1432-1033.1974.tb03767.x. [DOI] [PubMed] [Google Scholar]
- Sartorelli L., Fromm H. J., Benson R. W., Boyer P. D. Direct and 18-O-exchange measurements relevant to possible activated or phosphorylated states of myosin. Biochemistry. 1966 Sep;5(9):2877–2884. doi: 10.1021/bi00873a015. [DOI] [PubMed] [Google Scholar]
- Wolcott R. G., Boyer P. D. The reversal of the myosin and actomyosin ATPase reactions and the free energy of ATP binding to myosin. Biochem Biophys Res Commun. 1974 Apr 8;57(3):709–716. doi: 10.1016/0006-291x(74)90604-4. [DOI] [PubMed] [Google Scholar]