Time resolved measurements show that phosphate release is the rate limiting step on myofibrillar ATPases
- 1 May 1995
- journal article
- Published by Wiley in FEBS Letters
- Vol. 364 (1) , 59-62
- https://doi.org/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.Keywords
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