THE POSSIBLE INVOLVEMENT OF LH HCG INDUCED MITOCHONDRIAL PROTEINS IN THE REGULATION OF STEROIDOGENESIS IN BOVINE LUTEAL CELLS/

In previous studies we described the synthesis of three mitochondrial proteins (A, B and C) in response to acute in vitro stimulation by lut ropin of small bovine luteal cells. Protein A had a molecular weight o f 28 kDa and an isolectric point (pI) of 6.7. Proteins B and C had a m olecular mass of 27 kDa and pI of 6.2 and 6.4, respectively. The appea rance of these proteins was prevented by 100 mu M cycloheximide. In th e present study, we have shown that the time course of synthesis of pr otein A and its hCG dose-response closely parallel the increase in pro gesterone production. The induction by hCG of protein A was already ob served after a 5 min incubation. Pulse chase experiments by addition o f excess unlabelled methionine after prelabelling with [S-35]methionin e indicated that its half-life was approximately 15-20 min. Study of P -32 labelled phosphate incorporation into individual proteins and trea tment by alkaline phosphatase of [S-35]methionine-labelled proteins de monstrated that none of the three proteins A, B or C was a phosphoprot ein. Localization of protein A in mitochondria, at the site of the rat e limiting step in steroidogenesis, and the high degree of correlation between its S-35 labelling and progesterone production argue in favou r of its involvement in the acute regulation of steroidogenesis. Copyr ight (C) 1996 Elsevier Science Ltd.