STUDIES ON MITOCHONDRIAL PROTEIN-KINASE ACTIVITY OF PORCINE CORPORA-LUTEA

Activation of mitochondrial protein kinase and its role in regulation of [4-14MC]cholesterol conversion to [4- 14C]pregnenolone and [4-14C]progesterone were studied using mitochondria prepared from porcine corpora lutea. The presence of a cAMP-dependent protein kinase in luteal mitochondria was confirmed by using highly purified samples prepared by large scale zonal centrifugation. Slices of corpora lutea secreted almost 3 times more progesterone when incubated for 30 min with 10 μg LH/ml. The LH treatment of luteal tissue also resulted in an increase in endogenous protein kinase activity (measured without cAMP) of mitochondria from 45.0 to 60.7 pmol 32P/mg protein min. However, the LH treatment of corpora lutea did not significantly change [4-14C]cholesterol conversion activity. When isolated intact luteal mitochondria were incubated with cAMP, almost all of themitochondrial protein kinase was activated, but there was no change in the [4-14C]cholesterol conversion activity of these mitochondria. The addition of partially purified cytosol protein kinase to a crude preparation of the cholesterol side chain cleavage enzyme complex from luteal mitochondria caused a 2-fold increase in [4- 14C]cholesterol conversion activity. However, the addition of the cytosol protein kinase to intact luteal mitochondria had no significant effect on their [4-14C]cholesterol conversion activity. It is concluded that in vitro treatment of luteal tissue with LH activates mitochondrial protein kinase, probably through cAMP. However, the reason for the lack of stimulation of [4-l4C]cholesterol conversion in these studies is not apparent and warrants further investigation. © 1979 by The Endocrine Society.