Protein phosphorylation in the corpus luteum

Soluble luteal extracts were incubated with putative second messengers or regulators of protein kinases in the presence of [gamma-32P]ATP, and proteins were separated by SDS-PAGE. There was a novel phosphorylation of a protein of Mr 80,000 which was stimulated by phospholipid and 1,2-diacylglycerol but, unlike classical C-kinase phosphorylating activity, was increased by EGTA and reduced by Ca2+. This phospholipid/diolein-stimulated phosphorylation of a Mr 80,000 protein was detectable in rat and pig luteal extracts and was enhanced 2-fold in rabbit CL by administration of oestradiol-17 beta in vivo. These results suggest that the luteotrophic functions of oestradiol in rabbit CL are mediated in part by regulating either the kinase and/or the Mr 80,000 substrate.