Phosphorylation of protein components of isolated zymogen granule membranes from the rat pancreas

Some properties were examined of the isolated membranes of zymogen granules from the rat pancreas. It was possible to detect an endogenous protein kinase activity capable of phosphorylating 8 to 10 membrane protein constituents as well as added histones. Cyclic adenosine monophosphate (AMP), and cyclic guanosine monophosphate (GMP), to a lesser extent, exerted moderate stimulatory effects. These effects of cyclic nucleotides on membrane phosphorylation became more apparent upon addition of a partially purified soluble protein kinase also extracted from the rat pancreas.