Isolation of Golgi fractions from colchicine-treated rat liver. II. Electrophoretic characterization

1. Intact Golgi fractions, three from colchicine- or ethanol-treated rat livers and two from a control, were analyzed by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. All the fractions showed very similar electrophoretic profiles with 33 protein bands, some of which, especially albumin, had rather higher density in the secretory vesicle fraction than those in the cisternal fraction. 2. Using albumin as the content marker, the Golgi fractions were subfractionated into membranes and contents by freezing-thawing and sonication followed by centrifugation. Distribution of galactosyltransferase among these membrane preparations showed that this enzyme was more enriched in the Golgi cisternal membranes than in the secretory vesicle membranes. 3. All the membrane preparations from the Golgi complex showed very similar patterns on electrophoresis, which were distinctly different from those of microsomal membranes and of plasma membrane. Furthermore, all the Golgi content subfractions had similar protein components, most of which were also found in serum. The microsomal contents, however, showed a considerably different pattern from those of the Golgi contents. 4. From these results it could be concluded that the secretory vesicles are indeed a member of the Golgi complex despite their different appearance and morphology.