Membrane fusion and glycosylation in the rat hepatic Golgi apparatus.

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Abstract
When purified Golgi fractions were incubated with UDP-[3H]galactose in the absence of Triton-X-100, radioactivity was incorporated into an endogenous lipid and several peptide acceptors. EM analysis of Golgi fractions incubated in the endogenous galactosyl transferase assay medium revealed extensive fusion of Golgi saccules. Systematic removal of constituents in the galactosyl transferase assay medium showed enhanced (minus .beta.-mercaptoethanol) or reduced (minus ATP, minus sodium cacodylate buffer or minus MnCl2) fusion of Golgi membranes compared to the complete medium. Stereologic analysis revealed a correlation betweem membrane fusion and galactosyl transferase activity (r = 0.99, P, P < 0.0001). Electron microscope radioautography was carried out after incubation of Golgi fractions with UDP-[3H]galactose. Ag grains were not observed over trans elements of Golgi but were revealed mainly over large fused saccules with the number of Ag grains being proportionate to membrane fusion (r = 0.92, P < 0.001). Bilayer destabilization at points of Golgi membrane fusion may act to translocate galactose across the Golgi membrane and thereby provide a fusion regulated substrate for terminal glycosylation.