Abstract
Two species of casein kinase from lactating bovine mammary gland have been identified; a Ca2+‐ and CM‐independent casein kinase and a Ca2+‐ and CM‐dependent casein kinase. The Ca2+‐ and CM‐independent casein kinase phosphorylates previously dephosphorylated αs1‐, β‐ or κ‐casein while the Ca2+‐ and CM‐dependent casein kinase prefers previously dephosphorylated β‐ or κ‐casein as substrates. Two activities are indicated by their substrate specificity, sensitivity to Ca2+ and CM, pH maxima, and differential solubilization by anionic detergents. The presence of a regulated casein kinase in the lactating mammary gland suggests that casein phosphorylation may be a regulator of micelle formation or secretion.