Calmodulin and Ca2+‐ and Calmodulin‐Dependent Protein Kinase in Rat Anterior Pituitary Gland

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Abstract
Calmodulin and Ca2+- and calmodulin-dependent protein kinase were identified in the rat anterior pituitary gland. The concentration of calmodulin was 1.18 ± 0.11 μg/mg protein (n = 7) in the cytosol fraction. The calmodulin of the anterior pituitary gland co-migrated with brain calmodulin on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The Ka value of the partially purified enzyme for Ca2+ was 3.3 μ.M in the presence of 0.30μ.M calmodulin. Trifluoperazine and chlorpromazine, calmodulin-interacting agents, inhibited enzyme activity, with Ki values of 1.3 and 2.6 x 10-5M, respectively. The enzyme was resolved into two peaks of activity, with sedimentation coefficients of 5.5 S and 16.5 S, by sucrose density gradient centrifugation. At least nine proteins were phosphorylated by the enzyme in a Ca2+- and calmodulin-dependent manner. In light of these results, the possibility that calmodulin and the calmodulin-activatable protein kinase system are involved in the mediation of the Ca2+ effect on hormone release from the anterior pituitary gland must be given consideration.