The acute anti-lipolytic effect of human growth hormone (hGH) in maximally noradrenaline-stimulated intact rat adipocytes was selectively associated with increased phosphorylation of a 46 kDa plasma membrane protein which was highly enriched by hGH-Sepharose chromatography. The same protein was also phosphorylated by an endogenous protein kinase in isolated plasma membranes, although then no hGH effect could be demonstrated. About 14% of the phosphate incorporated into the protein in isolated plasma membranes was found in tyrosine residues and the remainder in serine and threonine. The possible relation of the 46 kDa protein with the hGH plasma membrane receptor is discussed.
