Ionic Interactions Play a Role in the Regulatory Mechanism of Scallop Heavy Meromyosin
- Nyitrai, M.
- Stafford, W.F.
- Szent-Györgyi, A.G.
- Geeves, M.A.
DOIAbstract
AbstractHeavy meromyosin from scallop (scHMM) striated muscle is regulated by calcium binding to the essential light chain. The regulation can be modeled with a calcium-dependent equilibrium between on and off scHMM conformations. The observed rate constant for mant-ADP dissociation from scHMM is calcium dependent, and we show here that it can be used to define the equilibrium constant (Keq) between on and off conformations. The data show that Keq is markedly ionic strength dependent, with high salt (≥200mM) abolishing the off state even in the absence of calcium and low salt (<50mM) favoring the off state even in the presence of calcium. Debye-Huckel plots of the equilibrium constant (Keq) for the on and off forms gave parallel slopes (5.9...
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