Abstract
Three protein kinases that are stimulated by adenosine 3’,5’-monophosphate (cyclic AMP) have been isolated from bovine thyroids by ion-exchange and gel-filtration chromatography. One of these kinases has a molecular weight of about 76,000, with a pH optimum of 7.5 both in the presence and absence of cyclic AMP. This peak of kinase activity phosphorylates protamine sulfate more rapidly than histone, but the phosphorylation of protamine is not cyclic AMP-dependent. The other two peaks of kinase activity have molecular weights of 102,000 and 191,000, but otherwise appear similar in their characteristics. Both show a pronounced pH optimum of 6.5 in the presence of cyclic AMP, but little pH effect in its absence. These two peaks of kinase activity phosphorylate histone and protamine nearly equally, although cyclic AMP stimulates their phosphorylation of histone more than protamine. (Endocrinology 91: 1343, 1972)
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