The biosynthesis and secretion of α2-macroglobulin was studied in rat hepatocytes primary cultures. After immunoprecipitation of α2-macroglobulin from a cell homogenate and the hepatocyte medium, two forms of α2-macroglobulin with app. M r of 176000 and 182000, respectively, were identified. A precursor—product relationship for the two α2-macroglobulin forms was demonstrated by a pulse-chase experiment. The cellular form of α2-macroglobulin could be deglycosylated by endoglucosaminidase H, whereas the medium form of α2-macroglobulin remained unaffected. On the other hand, only the medium form of α2-macroglobulin was found to be susceptible to neuraminidase. In vitro translation of rat liver poly(A)+ RNA resulted in a translation product of an app. M r of 162000.
