Characterization of Calf‐Ovary Adenosine‐3′: 5′‐Monophosphate‐Dependent Protein Kinases and Adenosine‐3′: 5′‐Monophosphate‐Binding Proteins

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Abstract
Protein phosphokinase activity from the calf ovary cytosol (105000 × g supernatant fraction) has been resolved by chromatography and polyacrylamide gel electrophoresis into two major pro‐tein kinases, PK‐H1 and PK‐H2, both dependent on adenosine 3′: 5′‐monophosphate (cyclic AMP). The enzymes have similar molecular weights (230000) and substrate specificities but differ in their cyclic‐AMP‐dependency and stimulation by cyclic AMP. The differences have been explained by the presence in PK‐H1 of a unique cyclic‐AMP‐binding protein which has little catalytic activity as‐ sociated with it. The cyclic‐AMP‐binding protein has a high affinity for cyclic AMP and in addition is able to inhibit the activity of the isolated catalytic subunit.The ovarian cyclic‐AMP‐dependent protein kinases have properties similar to those found in other tissues. They can be dissociated into catalytic and regulatory subunits and are inhibited by a heat‐stable protein inhibitor isolated from rabbit skeletal muscle.Preincubation of the cytosol with high levels of cyclic AMP resulted in additional cyclic‐AMP‐dependent protein kinases and cyclic‐AMP‐binding proteins which include protein kinases and binding proteins of > 400000 molecular weight.