A NOVEL PROTEIN PHOSPHATASE-1 INHIBITORY PROTEIN POTENTIATED BY PROTEIN-KINASE-C - ISOLATION FROM PORCINE AORTA MEDIA AND CHARACTERIZATION

A novel phosphorylation-dependent inhibitory protein (IF) of porcine a orta myosin light chain phosphatase (PA-MLCP) was purified to homogene ity from porcine aorta media, The molecular mass of IP was 20 kDa. TP phosphorylated by endogenous potentiating kinase (IP-K) inhibited not only PA-MLCP activity, but also that of the catalytic subunit of prote in phosphatase-l. The amino acid sequence of a peptide derived from IP phosphorylated with IP-K, RHARVTVK, shared one of the consensus sequ ences phosphorylatable by protein kinase C (PKC), where T was phospho rylated, IP was phosphorylated by PKC and the phosphorylated product i nhibited PA-MLCP as strongly as TP phosphorylated with IP-K.