CALMODULIN AND MYOSIN LIGHT-CHAIN KINASE OF RABBIT FAST SKELETAL-MUSCLE

It is confirmed that myosin light-chain kinase is a protein of mol.wt. about 80 000 that is inactive in the absence of calmodulin. In the presence of 1 mol of calmodulin/mol of kinase 80-90% of the maximal activity is obtained. Crude preparations of the whole light-chain fraction of rabbit fast-skeletal-muscle myosin contain enough calmodulin to activate the enzyme. A procedure is described for the isolation of calmodulin from rabbit fast skeletal muscle. Rabbit fast-skeletal-muscle calmodulin is indistinguishable from bovine brain calmodulin in its ability to activate myosin light-chain kinase. The other properties of these two proteins are also very similar. Rabbit fast-skeletal-muscle troponin C was about 10% as effective as calmodulin as activator for myosin light-chain kinase. By chromatography of a Ca2+-dependent complex between calmodulin and myosin light-chain kinase. Troponin I from rabbit fast skeletal muscle and histone IIAS were phosphorylated by fully activated myosin light-chain kinase at about 1% of the rate of the P light chain.