Isolation and Characterization of Glycopeptides from Rat Liver Nuclear Membrane*

Abstract

Isolated nuclei from rat liver contained carbohydrates consisting mainly of glucosamine and mannose which are normally components of glycoproteins. About 60% of the glucosamine and all of the mannose were localized in the nuclear membranes with nearly equal distribution between outer and inner membranes. Glycopeptides were prepared by pronase digestion from isolated membrane, then fractionated to produce neutral and acidic glycopeptide fractions. The neutral one was major, comprising 74% of the total glucosamine, and its carbohydrate moiety consisted mainly of glucosamine and mannose with a molar ratio of about 1:3. This composition is very similar to that of the corresponding glycopeptide fraction from hepatic microsomes. Metabolic studies using ¹⁴C-glucosamine suggested that carbohydrate moieties of the nuclear membrane are synthesized in nuclei or their vicinity.