Adenylate cyclase in the maturing human reticulocyte: selective loss of the catalytic unit, but not of the receptor-cyclase coupling protein.

Abstract

Hormone sensitive adenylate cyclase consists of at least three components; hormone receptor, a catalytic unit, and the N-protein, which couples the receptor to the catalytic unit. Human erythrocytes have very low adenylate cyclase activity, but do have N-protein activity. We have investigated the fate of the catalytic unit and the N protein during maturation of human reticulocytes. We compared red blood cell membranes derived from nine patients with reticulocytosis averaging 12% to erythrocyte membranes from eight normal subjects. The catalytic unit was assayed by stimulation of adenylate cyclase with forskolin, and the N-protein activity by an in vitro complementation assay. Forskolin stimulated adenylate cyclase activity was ten times higher in membranes derived from patients with reticulocytosis as compared with those of normal subjects. N-protein activity was only slightly (12%) and insignificantly (P = 0.08) higher in the reticulocytosis patients membranes. We conclude that during maturation of the human erythrocyte there is a differential loss of the catalytic unit of adenylate cyclase.