Demembranated Muscle Fibers Catalyze a More Rapid Exchange between Phosphate and Adenosine Triphosphate than Actomyosin Subfragment 1

Bowater, R. and Sleep, J. (1988) Demembranated Muscle Fibers Catalyze a More Rapid Exchange between Phosphate and Adenosine Triphosphate than Actomyosin Subfragment 1. Biochemistry, 27 (14). pp. 5314-5323. ISSN 0006-2960

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Abstract

The rate of ATP ⇌ Pi exchange, that is, the incorporation of medium Piinto ATP during the net hydrolysis of ATP, has been measured for rabbit psoas muscle fibers, myofibrils, and actomyosin subfragment 1 (acto-Sl). The maximum exchange rate in fibers at saturating [Pi] is 0.04 s-1per myosin head at 8 °C, pH 7, and an ionic strength of 0.2 M. The dependence of the rate on Piconcentration can be approximated by a hyperbola with an apparent dissociation constant (km) of 3 mM. Myofibrils catalyze ATP ⇄ Pi exchange with a similar Kmbut at a slightly lower rate. In contrast, the soluble acto-Sl system, in which ATP hydrolysis is not coupled to tension generation, catalyzes exchange at a rate 500 times lower than that of fibers at low Piconcentration, and the Kmfor Piis greater than 50 mM. The difference between the ATP ⇌ Piexchange of fibers and of acto-Sl is discussed in terms of a model in which Pi binds to a force-generating state AM′₷ADP and, due to mechanical constraint, the average free energy of this state is higher in the fiber than in acto-Sl.

Item Type:	Article
Uncontrolled Keywords:	biochemistry ,/dk/atira/pure/subjectarea/asjc/1300/1303
Related URLs:	https://www.scopus.com/pages/publication...
Depositing User:	LivePure Connector
Date Deposited:	26 May 2026 12:49
Last Modified:	31 May 2026 05:28
URI:	https://ueaeprints.uea.ac.uk/id/eprint/103149
DOI:	10.1021/bi00414a055

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