title: Lipid requirement of membrane-bound 3-oxosteroid delta4-delta5-isomerase. Studies on beef adrenocortical microsomes.
abstract: The role of phospholipid in the beef adrenal microsomal 3-oxosteroid delta4-delta5-isomerase (EC 5.3.1.1) has been investigated with the use of phospholipase A to alter the microsomal phospholipids. The byproducts of phospholipase A digestion have been removed with a wash solution containing bovine serum albumin. Removal of 80-85% of the phospholipid leads to loss of 80-90% of the 3-oxosteroid delta4-delta5-isomerase activity. Reconstitution experiments have been performed by introduction of lipid aqueous dispersions in the enzymatic assay. Asolectin, a commercially available preparation of soy phosphatides, is able to stimulate the enzymatic activity but does not restore the 3-oxosteroid delta4-delta5-isomerase activity in phospholipase-A-treated membranes. In contrast, the introduction of aqueous dispersions of microsomal total lipid mixtures in the enzymatic assay brings about a complete restoration of the 3-oxosteroid delta4-delta5-isomerase activity in the lipid-depleted membranes. It is concluded that the bovine adrenal microsomal 3-oxosteroid delta4-delta5-isomerase requires phospholipid(s) to exhibit its full catalytic activity.
mesh_terms: D000302:Adrenal Cortex / Q000201:enzymology*; D000311:Adrenal Glands / Q000201:enzymology*; D000818:Animals; D002417:Cattle; D066298:In Vitro Techniques; D007535:Isomerases / Q000378:metabolism*; D008861:Microsomes / Q000201:enzymology* / Q000378:metabolism; D010740:Phospholipases / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism* / Q000494:pharmacology; D013251:Steroid Isomerases / Q000378:metabolism*
chemical_list: D010743:Phospholipids; D010740:Phospholipases; D007535:Isomerases; D013251:Steroid Isomerases