four hypotheses were considered : 1 ) reduced substrate , i.e. , atp depletion , 2 ) altered access of either the myosin kinase or phosphatase to the cross bridge , 3 ) reduced myosin kinase activity secondary to its phosphorylation by adenosine 3',5'-cyclic monophosphate-dependent protein kinase , and 4 ) reduced myoplasmic [ ca2+ ] during the contraction .
C0031715
phosphorylation
C0033640
protein