Calcium-, calcium/calmodulin-, and calcium/phospholipid-stimulated protein phosphorylation in the rat anterior pituitary. |
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Authors: | J C Pryor S T Cain C B Nemeroff |
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Affiliation: | Department of Psychiatry, Duke University Medical Center, Durham, North Carolina 27710. |
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Abstract: | Calcium-dependent protein phosphorylation may be a critical step in the stimulated secretion of anterior pituitary hormones. We have noted the existence of a number of calcium-calcium/calmodulin-, and calcium/phospholipid-dependent phosphoproteins in the normal rat anterior pituitary. Cell extracts were prepared from anterior pituitary glands of male rats and phosphorylated with [gamma 32P]ATP in the presence or absence of calcium, calmodulin, and phosphatidylserine. The samples were electrophoresed on SDS-PAGE gels, autoradiographs prepared, and phosphate incorporation into specific proteins quantitated with microdensitometry. Calcium alone significantly stimulated the phosphorylation of proteins with molecular weights of 80.0-, 62.0-, 51.0-, 30.5-, and 25.0-kDa. The phosphorylation of 21.5-, 51.0-, and 80.0-kDa MW phosphoproteins was found to be phospholipid dependent. The phosphorylation of 62.0-, 51.0-, 33.0-, 30.5-, and 25.0-kDa MW phosphoproteins was found to be calcium/calmodulin kinase dependent. Calcium/calmodulin also inhibited phosphorylation of the 80.0-kDa phosphoprotein. |
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Keywords: | Protein phosphorylation Phospholipids Calcium Calmodulin Anterior pituitary Protein kinase C |
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