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 aorta myosin light chain phosphatase (PA-MLCP) was purified to homogeneity 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 protein phosphatase-l. The amino acid sequence of a peptide derived from IP phosphorylated with IP-K, RHARVT*VK, shared one of the consensus sequences phosphorylatable by protein kinase C (PKC), where T* was phosphorylated, IP was phosphorylated by PKC and the phosphorylated product inhibited PA-MLCP as strongly as TP phosphorylated with IP-K.