Localization of the enzyme system for glycosylation of proteins via the lipid-linked pathway in rough endoplasmic reticulum.

A crude preparation of microsomal membranes (postmitochondrial supernatant fraction) from the magnum portion of the hen oviduct was further subfractionated using a discontinuous sucrose gradient. Preparations of purified smooth surfaced membranes and rough endoplasmic reticulum, characterized by electron microscopy and nucleic acid content, were isolated. The enzymes involved in formation of mannose-containing glycoproteins via the lipid-linked pathway were shown to be localized in the rough endoplasmic reticulum. In contrast, a galactosyltransferase that catalyzed transfer of galactose to asialo-agalacto-orosomucoid was localized in the smooth membrane fraction. There was no evidence for the involvement of lipid intermediates in the galactosyl transfer observed in this fraction.