Oxygen exchange between Pi in the medium and water during ATP hydrolysis mediated by skinned fibers from rabbit skeletal muscle. Evidence for Pi binding to a force-generating state

J Biol Chem. 1986 Nov 25;261(33):15557-64.

Abstract

Oxygen exchange between (18O4)Pi in the medium and water accompanies ATP hydrolysis catalyzed by the calcium-regulated MgATPase of vertebrate skeletal muscle. Exchange was observed in chemically skinned fibers from rabbit psoas muscle held isometrically and activated by 30 microM free Ca2+. The rate of exchange was approximately proportional to Pi concentration (up to 10 mM) and was characterized by an apparent second order rate constant greater than or equal to 475 M-1 S-1 (pH 7.1, ionic strength 0.2 M, 22 degrees C). Much less exchange occurred in the absence of Ca2+ or when ATP was replaced by ADP. It has been inferred from mechanical experiments that Pi can bind to a force-generating ADP-bound state of actomyosin with resultant suppression of force (Hibberd, M. G., Dantzig, J. A., Trentham, D. R., and Goldman, Y. E. (1985) Science 228, 1317-1319). The oxygen exchange results support this inference by providing direct evidence that Pi in the medium binds at the ATPase catalytic site in activated isometric fibers. The inter-relationship of these two effects involving Pi on mechanochemical coupling in muscle is discussed.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Diphosphate / metabolism
  • Adenosine Triphosphate / metabolism*
  • Animals
  • Ca(2+) Mg(2+)-ATPase / metabolism*
  • Calcium / pharmacology
  • Hydrolysis
  • Kinetics
  • Muscle Contraction
  • Muscles / enzymology*
  • Oxygen / metabolism*
  • Oxygen Isotopes
  • Phosphates / metabolism*
  • Rabbits
  • Water / metabolism

Substances

  • Oxygen Isotopes
  • Phosphates
  • Water
  • Adenosine Diphosphate
  • Adenosine Triphosphate
  • Ca(2+) Mg(2+)-ATPase
  • Oxygen
  • Calcium