Identification of a major endogenous substrate for phospholipid/Ca2+-dependent kinase in pancreatic acini as Gc (vitamin D-binding protein).

A major 56 kDa substrate for phospholipid/Ca2+-dependent kinase (C-kinase) in pancreatic acinar cells is physicochemically and immunologically indistinguishable from the vitamin D-binding protein, Gc or group-specific component. Cellular Gc was also phosphorylated in intact cells following treatment with carbachol as a physiological stimulus. These findings indicate the potential usefulness of Gc as a defined substrate for further studies of the biological role of C-kinase activity in pancreatic acini and possibly in other cells.