PHOSPHORYLATION OF MYOSIN-I FROM RAT-LIVER BY PROTEIN-KINASE-C REDUCES CALMODULIN-BINDING

Three isoforms of the cytoskeletal-associated, mechanochemical enzymes known as myosin-I have been purified from rat liver; each coisolates with calmodulin. Incubation of the purified myosin-I's with protein ki nase C gamma and P-32- ATP results in phosphorylation of the myosin-I heavy chains. After phosphorylation, the myosin-I isoforms bind less r adiolabeled calmodulin in binding assays than observed for control sam ples. Since the purified isoforms are phosphoproteins as determined by immunoblotting with monoclonal antibodies which recognize phosphoamin o acids, these results indicate that phosphorylation might play a role in regulation of myosin-I. (C) 1995 Academic Press, Inc.