DISTRIBUTION OF CALCIUM CALMODULIN-DEPENDENT PROTEIN KINASE-II IN RATILEAL ENTEROCYTES

Ca2+/calmodulin (CaM)-dependent protein kinase II is a major effector of the Ca2+ signaling pathway. It has a wide tissue distribution and p hosphorylates multiple substrates. Villus enterocytes from rat ileum c ontain a Ca2+/CaM-dependent kinase activity that phosphorylates the ex ogenous neural substrate synapsin I. This phosphorylation is blocked b y a specific peptide inhibitor. Antibodies made to rat brain Ca2+/CaM- dependent protein kinase II label a single band with a relative molecu lar mass of approximately 50 kDa in isolated rat enterocytes by immuno blot. Almost one-half of this immunoreactive protein is preferentially found in a particulate compared with a soluble subcellular fraction o f the enterocytes. Virtually all of the 50-kDa band in the particulate fraction is insoluble in nonionic detergent, suggesting that the kina se is associated with the enterocyte cytoskeleton. Antibodies to Ca2+/ CaM-dependent protein kinase II immunocytochemically detect fibrillar structures concentrated in the terminal web region of intestinal epith elial cells that colocalized with myosin II. This enzyme may have a ro le in regulating the intestinal epithelial cytoskeleton.