Phosphorylation of molluscan paramyosin.

1. In Mytilus edulis two proteins of the contractile apparatus can be phosphorylated by cyclic AMP dependent protein kinases: a 295,000 d protein of unknown function, and paramyosin. 2. Paramyosin isolated from thick filaments by the selective extraction method contains the 106,000 d monomer only, whereas paramyosin extracted from ethanol ether dried powder contains equal amounts of the 108,000 d, and the 106,000 d monomers, and traces of the 104,000 d monomer. 3. Paramyosin isolated from ethanol ether dried powder incorporates up to four times the amount of 32P than paramyosin isolated by the selective extraction method. 4. Cytoplasmatic protein kinases show a higher affinity towards paramyosin as a phosphoryl acceptor than protein kinases associated with paramyosin. 5. Paramyosin of 5-HT treated catch muscles is phosphorylated 2 to 4 times better than paramyosin of ACh treated or untreated catch muscles.