Stimulation of cholesterol binding to steroid-free cytochrome P-450scc by poly(L-lysine). The implication in functions of labile protein factor for adrenocortical steroidogenesis.

Abstract

At the low concentration of 2 nM, poly(L-lysine) stimulated the binding of dioleoylglycerophosphocholine liposomal cholesterol to steroid-free cytochrome P-450scc, which was purified from bovine adrenocortical mitochondria. Ca2+ and K+ ions displayed similar effects at much higher concentrations. These stimulatory effects were more significant at lower temperatures. Regardless of the presence of these activators, the maximal binding of cholesterol was observed between 20 and 30 mol % in dioleoylglycerophosphocholine liposomes. The examination of phospholipid fatty acyl groups on the cholesterol binding revealed that the initial binding rates decreased in the following order: (18c:2) greater than (18c:1) greater than (18c:3) greater than 18t:1) greater than (18c:1, 18:0) in the presence and absence of the lysine polypeptide. When 7 alpha-, 7 beta-, and 25-hydroxycholesterol were used as ligands, the stimulatory effect of the lysine polypeptide was not seen, indicating the specificity for cholesterol. When the cholesterol side chain cleavage activity was determined by the reconstituted system consisting of adrenodoxin reductase, adrenodoxin, and P-450scc, the stimulatory effects by poly(L-lysine) were observed. Polyglycine, poly(L-glutamic acid), putrescine, spermidine, spermine, and L-lysine had no effect, while poly(D-lysine) and poly(L-arginine) had activities much less than the lysine polypeptide.