Human serum lipoproteins activate adipocyte plasma membrane adenylate cyclase

Abstract

BROWN and Goldstein¹ and Stein et al.², have shown evidence for the role of a specific cell surface receptor in the binding and catabolism of serum low-density lipoproteins (LDL) by cultured human fibroblasts. This receptor does not seem to be unique to fibroblasts however, since it has been shown that circulating human lymphocytes³, human fat cells⁴ and cultured smooth muscle cells⁵ may also bind LDL; also, binding sites for LDL and very low density lipoproteins (VLDL) seem to be present in crude membrane preparations from various organs and tissues of the pig⁶. These findings suggest that lipoprotein receptors are ubiquitous in mammalian cells and raise the possibility that occupancy of such surface binding sites might modify some aspect of membrane function. Evidence for an alteration of membrane function by lipoproteins was recently reported by Shore and Shore⁷, who observed that human serum VLDL and LDL were capable of specifically activating the human erythrocyte membrane Mg²⁺-ATPase.