Synthesis of Mitochondrial Proteins after Stimulation of Ovarian Follicles by Luteinizing Hormone*

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Abstract
Treatment of isolated ovarian follicles with LH results in an increase in pregnenolone and progesterone secretion. Furthermore, LH treatment of follicles increases mitochondrial cholesterol conversion activity but does not significantly affect the mitochondrial ATP synthesis rate. Since these changes in pregnenolone synthesis may be due, at least in part, to changes in the components of mitochondria, we investigated the synthesis of mitochondrial proteins in response to treatment of follicles with LH. Follicles (4–6 mm in diameter) were isolated from porcine ovaries and incubated for 24 h without or with LH (1<μg/ml medium 199D), in the presence of [3H]leucine (without LH) or [14C]leucine (with LH). Untreated and LH-treated follicles were combined, and a mitochondrial sample was prepared. The mitochondrial proteins were separated by sodium dodecyl sulfate-gel electrophoresis using 8% and 15% polyacrylamide gels, and the 14C to 3H ratio of slices was determined. General incorporation of radiolabeled leucine into follicular mitochondria was linear for at least 24 h. The relative amounts of leucine incorporated into several mitochondrial proteins were similar for samples from untreated and LH-treated follicles. However, LHtreated follicles consistently incorporated more than twice as much leucine into low molecular (mw) mitochondrial protein (s) than did untreated follicles. The specific protein (s) has a mw of approximately 5000–6000 daltons and is extractable with acidic chloroform-methanol, suggesting that it may be a proteolipid. Sephadex LH-20 column chromatography of chloroform-methanol-soluble material confirmed the synthesis of such a mitochondrial component(s) in LH-treated follicles. In summary, these experiments show that treatment of follicles with LH enhances the synthesis of one or more low mw hydrophobic mitochondrial protein(s). While the function of the protein(s) is unknown, its synthesis correlates with changes in cholesterol conversion activity.