On the mechanism of action of follicle-stimulating hormone on aspartate aminotransferase in the rat ovary

The mechanism of action by which follicle-stimulating hormone (FSH) increases the activity of aspartate aminotransferase in the ovary has been investigated with the followings: 1. 1. It was shown by electrophoretic separation of subcellular fractions of normal and gonadotrophin-stimulated rat ovaries, and by immunochemical experiments, that the activities of both isoenzymes are increased as the result of gonadotrophic stimulation. 2. 2. The greater part of the cathodic isoenzyme is present in the mitochondrial fraction in a latent state, and can be activated by sonication of the mitochondrial fraction. 3. 3. The extent of activation depends on the previous hormonal stimulation of the ovaries from which the mitochondrial fraction is derived. Uninjected rat ovaries contain much more enzyme in the latent state than gonadotrophin-stimulated ovaries. 4. 4. Sonication activates only the cathodic enzyme. This is shown by electrophoretic separation of the enzyme forms and by immunochemical determination of the isoenzyme. 5. 5. It is concluded that FSH increases the activity of the cathodic isoenzyme of aspartate aminotransferase by activating a part of the latent enzyme present in the mitochondrial fraction. No explanation can yet be given for the increased activity of the anodic iso-enzyme by the action of the hormone.