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Phosphorylation of vertebrate smooth muscle and nonmuscle myosin heavy chains in vitro and in intact cells

Summary In this article we summarize our recent experiments studying the phosphorylation of vertebrate myosin heavy chains by protein kinase C and casein kinase II. Protein kinase C phosphorylates vertebrate nonmuscle myosin heavy chains both in vitro and in intact cells. A single serine residue near the end of the helical portion of the myosin rod is the only site phosphorylated in a variety of vertebrate nonmuscle myosin heavy chains. There does not appear to be a site for protein kinase C phosphorylation in vertebrate smooth muscle myosin heavy chains. Casein kinase II phosphorylates a single serine residue located near the carboxyl terminus of the 204×103Mr, smooth muscle myosin heavy chain in vitro as well as in cultured smooth muscle cells. It does not phosphorylate the 200×103Mr smooth muscle myosin heavy chain. However, the site is present in vertebrate nonmuscle myosin heavy chains. The 204×103Mr myosin heavy chain of embryonic chicken gizzard smooth muscle is exceptional in not containing a site for casein kinase II phosphorylation.