Biosynthesis of gp160, the major trypsin-sensitive surface glycoprotein of macrophages.

Abstract

The biosynthetic origin was investigated of gp160, the trypsin- and plasmin-sensitive surface glycoprotein of caseinate-elicited macrophages from guinea pigs. Biosynthesized surface components were analyzed by reacting [35S]methionine-labeled macrophages with trinitrobenzene sulfonic acid and purifying trinitrophenyl-substituted surface proteins by immunoprecipitation. Identification of gp160 was based on its molecular weight and unique trypsin sensitivity. In addition, [35S]methionine-labeled surface and intracellular glycoproteins were purified by Lens culinaris lectin affinity chromatography. Both purification procedures demonstrated that gp160 is biosynthesized by elicited macrophages in culture. gp160 was first detected on the cell surface 60-80 min after pulse labeling; transit to the cell surface was almost maximal at 3 h. No evidence was found for intracellular accumulation of mature gp160, i.e. in time course experiments all [35S]methionine-labeled gp160 was sensitive to trypsin treatment of intact cells. However, [35S]methionine-labeled gp160 was not detected in pulse-labeled macrophages until 60 min of nonradioactive chase incubation, indicating the existence of a precursor form.