A calmodulin dependent protein kinase in parietal cells

An enriched population of isolated rabbit gastric parietal cells, from the fundic mucosa of New Zealand White rabbit, contained an active cytosolic calmodulin-dependant protein kinase activity with a prominent 100 kDa substrate (pp100). The latter focused as a doublet with isoelectric point of 6.8 – 7.0. The pp100 protein was phosphorylated only on threonine residues on a single tryptic peptide. Trifluoperazine inhibited the pp100 kinase activity with a K I of 10 – 15 μM. Addition of exogenous calmodulin was able to restore activity to uninhibited levels. A protein band with a molecular weight and phosphopeptide map identical to pp100, phosphorylated by calcium-dependent kinase, was also observed in rabbit pancreatic cytosol. The data suggest that a type III calmodulin-dependent kinase is present in parietal cell cytosol.