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Calcium and Calmodulin-Dependent Phosphorylation of -Casein by a Bovine Mammary Casein Kinase

Department of Veterinary Pathobiology, The Ohio State University, 1925 Coffey Road, Columbus 43210

ABSTRACT

A calcium and calmodulin-dependent -casein kinase activity has been described in the bovine mammary gland. This kinase required previously dephosphorylated -casein for substrate, thus suggesting a physiological role for this enzyme. The -casein kinase required magnesium and the presence of both calcium and calmodulin for full activity. Calmodulin concentrations of .32 µM achieved one-half maximal activation of this enzyme. The calcium and calmodulin-dependent -casein kinase was found in preparations of mammary acini and could be localized in a membranous fraction by centrifugation. The particles containing this activity had a high density (1.309 g/cc) and cofractionated with caseins, suggesting this enzyme may be present in secretory granules.