A survey of calmodulin-activated protein kinase activity in several tissues of Rattus rattus

1. In each of five tissues (brain, heart, spleen, mammary acini and pancreatic acini) the prominent endogenous protein substrate possessed a molecular weight between 51,900 and 56,800 on SDS gel electrophoresis. 2. Evidence was obtained for two species of protein substrate, differing slightly in molecular weight, which appear to be distributed in a tissue-specific manner. 3. One species, with a molecular weight of 52,900, was found in spleen, mammary acini and brain; the other species, with a molecular weight of 56,200, was found in heart and pancreatic acini. 4. The specific activity of calmodulin-activated protein kinase in homogenates varied from a high of 44 pmol/min/mg in brain to 4.2 pmol/min/mg in mammary acini. 5. Subcellular fractionation of these tissues demonstrated that most of the activity was found in the cytosolic fraction and a "light-particle" fraction obtained by ultracentrifugation, but the kinase was not associated with endoplasmic reticulum. 6. High concentrations of calmodulin were required to activate the protein kinase activity from each tissue. 7. Calmodulin concentrations producing half-maximal activation were 94 nM for brain, 377 nM for spleen, 132 nM for pancreatic acini, 350 nM for heart, and 117 nM for mammary acini. 8. The calmodulin-activated protein kinase activity in these tissues were similar, but the few differences in properties from tissue to tissue left open the possibility that multiple, calmodulin-activated kinase activities exist in these tissues.