A low-molecular-weight protein from rat liver that resembles ligandin in its binding properties

Abstract

A protein of s20,w 1.6S and MW 14,000, which binds covalently a metabolite of the aminoazodye carcinogen N,N-dimethyl-4-amino-3''-methylazobenzene, was isolated from rat liver cytosol from carcinogen-treated and normal rats. The protein binds noncovalently palmitoyl-CoA, fatty acids, bilirubin, sex steroids and their sulfates, bile acids and salts, bromosulfophthalein, diethylstilbestrol and 20-methylcholanthrene with a wide range of affinities. The protein is isolated as 3 components with isoelectric points of 5.0, 5.9 and 7.6 by a method involving isoelectric focusing. All 3 components have closely similar amino acid analyses, tryptic-peptide maps and UV spectra. Each single component redistributes into all 3 on further electrophoresis. The 3 forms differ in their binding characteristics, the form of pI 7.6 having the highest affinity for compounds bound noncovalently. The protein was identified immunologically in rat liver, small intestine, adipose tissue, skeletal muscle, myocardium and testis. The protein was compared with other hepatic binding-protein preparations of similar MW.