Rabbit ovarian protein kinases. III. Gonadotrophin-induced activation of soluble adenosine 3',5'-monophosphate-dependent protein kinases.

Cytosol of mature estrous rabbit follicles contains a single species of protein kinase, protein kinase 3, which can be classified as a type II cAMP-dependent protein kinase. Cytosol of functional rabbit corpora lutea (CL) contains, in addition to protein kinase 3, a second species of kinase activity, protein kinase 2, which can be classified as a type I cAMP-dependent protein kinase. These conclusions are based upon the relative dissociation and reassociation characteristics of the two holoenzymes in the presence and absence of 0.5 M NaCl after in vitro dissociation by cAMP, upon the effect of MgATP on salt- and basic protein-induced dissociation, and upon their relative elution from DEAE-cellulose. Protein kinase 3 in mature estrous rabbit follicles was rapidly activated after an iv injection of hCG. The activation was demonstrated by an increase of the protein kinase activity ratio as well as by the appearance of the free catalytic subunit of protein kinase upon Sephadex gel filtration. Maximal activation occurred within 10 min of in vivo hormone administration and required ovulatory doses of hormones with LH-like activity. Neither PRL, ACTH, epinephrine, nor a highly purified preparation of FSH promoted activation of the follicular protein kinase 3. Demonstration of protein kinase activation in follicles was achieved in the presence of 0.5 M NaCl in the homogenization media. After an iv injection of hCG, a partial activation of luteal protein kinases 2 and 3 was demonstrated, as reflected by the increase of the protein kinase activity ratio. These results implicate an important role for cAMP-dependent protein kinase 3 in LH action in rabbit ovarian follicles and for cAMP-dependent protein kinases 2 and 3 in LH action in rabbit CL.