Time resolved measurements show that phosphate release is the rate limiting step on myofibrillar ATPases

FEBS Lett. 1995 May 1;364(1):59-62. doi: 10.1016/0014-5793(95)00356-e.

Abstract

The myofibril is a good model to study the ATPase of the muscle fibre. When myofibrillar ATPase reaction mixtures are quenched in acid, there is a burst of Pi formation, due to AM.ADP.Pi or Pi, as shown in the scheme: AM+ATP<-->A.M.ATP<-->AM.ADP.Pi<-->AM.ADP+Pi<-->AM+ADP. Therefore, in the steady state, either AM.ADP.Pi or AM.ADP or both predominate. To determine which, we studied the reaction using a Pi binding protein (from E. coli) labeled with a fluorophore such that it is specific and sensitive to free Pi [Brune, M. et al. (1994) Biochemistry 33, 8262-8271]. We show that the Pi bursts with myofibrillar ATPases (calcium-activated or not, or crosslinked) are due entirely to protein bound Pi. Thus, with myofibrillar ATPases the AM.ADP.Pi state predominates.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism
  • Adenosine Diphosphate / metabolism
  • Adenosine Triphosphatases / metabolism*
  • Animals
  • Calcium / metabolism
  • Cross-Linking Reagents
  • Muscle Relaxation
  • Myofibrils / enzymology
  • Myofibrils / metabolism*
  • Myosins / metabolism
  • Phosphates / metabolism*
  • Psoas Muscles
  • Rabbits
  • Time Factors

Substances

  • Actins
  • Cross-Linking Reagents
  • Phosphates
  • Adenosine Diphosphate
  • Adenosine Triphosphatases
  • Myosins
  • Calcium