Biochemical and Structural Differences Between Porcine Ovarian Follicular and Luteal Mitochondria

Abstract

Mitochondria from intact follicles (6-10 mm) and corpora lutea of porcine ovaries were isolated and compared biochemically and structurally. With succinate as substrate, luteal mitochondria consumed oxygen at a rate four times greater than did follicular mitochondria. However, the ADP:O ratio (moles of ADP converted to ATP per atom of oxygen) was significantly lower in luteal mitochondria. Follicular mitochondria synthesized 8.9 µmoles ATP/mg protein/2 h, whereas luteal mitochondria synthesized 21.2 µmoles/mg protein/2 h. Also, luteal mitochondria converted five times more [4-¹⁴C]-cholesterol to [4-¹⁴C]-pregnenolone than did follicular mitochondria. The amounts of cytochrome aa₃ in follicular and luteal mitochondria were 0.052 and 0.15 nmoles/ mg protein, respectively, while the amounts of cytochrome P-450 were 0.011 and 0.21 nmoles/mg protein. Electron microscopic examination of nonsectioned isolated samples showed that luteal mitochondria were significantly larger than follicular mitochondria, It is concluded that luteal mitochondria are more active in steroidogenesis and energy production than are follicular mitochondria. These higher levels of activity in luteal mitochondria probably result, in part, from the presence of additional functional components as indicated by increases in mitochondrial size and amounts of cytochrome aa₃ and cytochrome P-450.