PHOSPHORYLATION OF A SYNTHETIC HEPTADECAPEPTIDE BY SMOOTH-MUSCLE MYOSIN LIGHT CHAIN KINASE

Abstract

A synthetic heptadecapeptide corresponding to part of the NH2-terminal 17 residues of chicken gizzard myosin light chain (Mr = 20,000), Ser-Ser-Lys-Thr-Thr-Lys-Arg-Pro-Gln-Arg-Ala-Thr-Ser-(P)-Asn-Val-Phe-Ser-NH2, was readily phosphorylated by the myosin light chain kinase isolated from the same tissue. The synthetic peptide was phosphorylated stoichiometrically at serine 13, the same residue phosphorylated in the parent protein. The apparent Km and Vmax for peptide phosphorylation was 90 microM and 1.3 mumol min-1 mg-1 compared to 10 microM and 22 mumol min-1 mg-1, respectively, for the myosin light chain. The synthetic heptadecapeptide acted as a competitive inhibitor for myosin light chain..