Interactions of Gonadotropins with Corpus Luteum Membranes. I. Properties and Distributions of Some Marker Enzyme Activities after Subcellular Fractionation of the Superovulated Rat Ovary*

Abstract

The properties of a number of enzyme activities of the superovulated rat ovary were studied to establish optimal assay conditions and specific assay procedures for each activity. The activities were chosen on the basis of their extensive use in other tissues of the rat as marker enzymes for the major cell organelles. Homogenates of superovulated rat ovaries were subjected to fractionation by differential rate centrifugation, and sedimentation profiles were constructed for each marker enzyme activity. The various subcellular fractions were also monitored by electron microscopy. The enrichment of fractions with particular organelles by electron microscopy and enrichment of the appropriate organelle marker enzyme activities correlated well. Sedimentation profiles of a number of plasma membrane marker enzymes demonstrated a marked discrepancy between hCG[human chorionic gonadotropin]-binding activity and 5''-nucleotidase-, alkaline phosphatase- and Mg2+-dependent ATPase, and basal, hCG-stimulated, and F-stimulated adenylate cyclase activities. Fractions enriched in hCG-binding and adenylate cyclase activities were subjected to further fractionation on discontinuous sucrose density gradients. The distributions of the various plasma membrane markers again indicated a partial dissociation between hCG-binding and adenylate cyclase activities of luteinized rat ovaries, suggesting the existence of 2 distinct major plasma membrane populations, with different buoyant densities, marker enzyme profiles and adenylate cyclase and hormone-binding levels.