PHOSPHORYLATION OF CARDIAC MYOSIN LIGHT CHAIN-2 BY PROTEIN-KINASE-C AND MYOSIN LIGHT-CHAIN KINASE INCREASES CA2+-STIMULATED ACTOMYOSIN MGATPASE ACTIVITY

Myosin light chain 2 (MLC2) phosphorylation in rat cardiac whole myosin by cardiac myosin light chain kinase (MLCK) or by protein kinase C (PKC) resulted in increased actin-stimulated myosin MgATPase activity. The phosphorylation also increased Ca2+-stimulated myofibrillar MgATPase activity upon substitution of the phosphorylated myosin into myofibrils. In addition, phosphorylation of MLC2 in myofibrils by MLCK increased both the Ca2+-sensitivity and maximum activity of the myofibrillar Ca2+-stimulated MgATPase activity. The latter effect was inhibited by PKC-phosphorylation of troponin I, troponin T and C-protein. A role for both PKC and MLCK in regulating cardiac myofibrillar activity, via phosphorylation of various contractile proteins, is indicated. © 1993 Academic Press. All rights reserved.