N-(6-phenylhexyl)-5-chloro-1-naphthalenesulfonamide, a novel activator of protein kinase C

Naphthalenesulfonamide derivatives were used to study the mechanism of regulation of Ca2+-dependent smooth muscle myosin light chain phosphorylation catalyzed by Ca2+-activated, phospholipid-dependent protein kinase (protein kinase C) and myosin light chain kinase. Derivatives such as N-(6-phenylhexyl)-5-chloro-1-naphthalenesulfonamide (SC-9), with a hydrophobic residue at the end of a hydrocarbon chain, stimulated Ca2+-activated, phospholipid-dependent myosin light chain phosphorylation in a Ca2+-dependent fashion. There was no significant effect of these compounds on Ca2+-calmodulin (CaM) dependent myosin light chain phosphorylation. On the other hand, derivatives with the guanidino or amino residue at the same position had an inhibitory effect on both Ca2+-phospholipid- and Ca2+-CaM-dependent myosin light chain phosphorylation. These observations suggest that activation of Ca2+-activated, phospholipid-dependent myosin light chain phosphorylation by naphthalenesulfonamide derivatives depends on the chemical structure at the end of hydrocarbon chain of each compound. SC-9 was similar to phosphatidylserine with regard to activation, and the apparent Km values for Ca2+ of the enzyme with this compound and phosphatidylserine were 40 microM and 80 microM, respectively. Kinetic analysis indicated that 12-O-tetradecanoylphorbol 13-acetate increased the affinity of the enzyme with SC-9 for calcium ion. However, kinetic constants revealed that the Km value of protein kinase C activated by SC-9 for substrate myosin light chain was 5.8 microM, that is, about 10 times lower than that of the enzyme with phosphatidylserine, and that the Vmax value with SC-9 was 0.13 nmol X min-1, that is, 3-fold smaller than that seen with phosphatidylserine.(ABSTRACT TRUNCATED AT 250 WORDS)