title: Subcellular fractionation of the porcine corpus luteum: sequestration of progesterone in a unique particulate fraction.
abstract: Homogenates of porcine corpus luteum were subjected to fractionation by differential-rate centrifugation or sucrose density gradient fractionation, with or without pretreatment with digitonin. Fractions of each gradient were assayed for a number of markers characteristic of the major intracellular organelles and cell-surface membranes, and for progesterone content. The majority of the progesterone content of homogenates of porcine corpus luteum was associated with a low-density particulate fraction which equilibrated at a buoyant density of 1.07-1.09 g/cm3. Pretreatment with digitonin increased the buoyant density of the progesterone-enriched fraction markedly (to 1.13-1.15 g/cm3) without causing release of steroid. The density distributions of progesterone content in control and digitonin-treated luteal gradient fractions were quite distinct from those of the major intracellular organelles and luteal cell-surface membranes. However, NADH-cytochrome C reductase activity (but not other endoplasmic reticulum markers) was also enriched in this fraction. The results suggest that most of the progesterone of the porcine corpus luteum is associated with a unique particulate fraction which is enriched in digitonin-reactive lipids and NADH-cytochrome C reductase activity.
authors.affiliation: Department of Obstetrics and Gynaecology, Centre for Reproductive Biology, Edinburgh.
authors.forename: T A
authors.initials: TA
authors.lastname: Bramley
authors.forename: G S
authors.initials: GS
authors.lastname: Menzies
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000032:analysis; D002499:Centrifugation, Density Gradient; D003338:Corpus Luteum / Q000032:analysis* / Q000201:enzymology; D004072:Digitonin / Q000494:pharmacology; D005260:Female; D009940:Organoids / Q000032:analysis; D011374:Progesterone / Q000032:analysis*; D013347:Subcellular Fractions / Q000032:analysis; D013552:Swine
chemical_list: D011374:Progesterone; D004072:Digitonin