Inhibition by Mg²⁺ of the Interaction of Ca²⁺ with Spin-Labeled g₂ Bound to Myosin

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According to the measurement of ESR spectrum, Ca²⁺ induced conformational changes of spin-labeled g₂ bound to myosin in the presence of 1mM Mg²⁺. The half-maximal changes were observed at pCa 6.8 and at pCa 3.7. Spin-labeled phosphorylated g₂ bound to myosin showed one transition at pCa 4.5, which shifted to pCa 6.5 after the dephosphorylation with E. coli alkaliphosphatase.