ADP, PPi, and AMPPNP act as competitive inhibitors of the ATPase of myofibrils and actomyosin subfragment 1, with inhibition constants for rabbit myofibrils of 0.17, 3, and 5 mM, respectively.
ADP, PPi, and AMPPNP act as competitive inhibitors of myofibrillar and acto-S1 ATPase, with AMPPNP inhibition constants being significantly larger than reported dissociation constants for fibers.
Adenosine 5'-diphosphate (ADP), inorganic pyrophosphate (PPi), and adenyl-5'-yl imidodiphosphate (AMPPNP) act as competitive inhibitors of the ATPase of myofibrils and actomyosin subfragment 1 (acto-S1). At I = 0.2 M, pH 7, and 15 degrees C, the inhibition constants for rabbit myofibrils are 0.17, 3, and 5 mM, respectively; the values for frog myofibrils at 0 degrees C are very similar, being 0.22, 1.5, and 2.5 mM. The inhibition constant of AMPPNP is about 2 orders of magnitude larger than the reported dissociation constant for fibers Marston, S. B., Rodger, C. D., & Tregear, R. T. (1976) J. Mol. Biol. 104, 263-276. A possible reason for this difference is that AMPPNP binding results in the dissociation of one head of each myosin molecule. The inhibition constants for rabbit acto-S1 cross-linked with 1-ethyl-3-3-(dimethylamino)propylcarbodiimide measured under the same conditions were 0.12, 2.6, and 3.5 mM for ADP, PPi, and AMPPNP, respectively. The inhibition of cross-linked and native acto-S1 was compared at low ionic strength and was found to be similar. The value for ADP is very similar to reported values of the dissociation constant whereas the inhibition constants for AMPPNP and PPi are an order of magnitude weaker Greene, L. E., & Eisenberg, E. (1980) J. Biol. Chem. 255, 543-548.
Sleep et al. (1986) studied this question. ADP, PPi, and AMPPNP was evaluated on Inhibition constants for ATPase of myofibrils and actomyosin subfragment 1. ADP, PPi, and AMPPNP act as competitive inhibitors of the ATPase of myofibrils and actomyosin subfragment 1, with inhibition constants for rabbit myofibrils of 0.17, 3, and 5 mM, respectively.