Differential activity of protein kinase C in alveolar and peritoneal macrophages

The characteristics of protein kinase C activity present in guinea pig alveolar and peritoneal macrophages have been compared and examined. The activity is predominantly cytosolic with preference for phosphatidyl serine as cofactor over other phospholipids. K(m) of protein kinase C for ATP is 30.30 and 54.05 microM in alveolar and peritoneal macrophages respectively. Scatchard plot analysis shows heterogenous binding sites for [3H]PDBu in alveolar macrophages in contrast to peritoneal macrophages showing homogeneous type of binding sites. PMA activates protein kinase C in a dose-dependent manner and shows downregulation at higher concentration in both alveolar and peritoneal macrophages. Endogenous proteins of molecular masses 77, 47, 37 and 16.5 kDa in alveolar macrophages and 77, 47, 38 and 15.5 kDa in pertioneal macrophages are phosphorylated by PKC. These findings suggest that alveolar and peritoneal macrophages possess two different types of protein kinase C activities but phosphorylate similar proteins and exhibit functional similarities in these cells.