The topography of gangliosides in the membrane of the chromaffin granule of bovine adrenal medulla.

We have studied the topography of the gangliosides of the adrenal chromaffin granules by using neuraminidase to remove sialic acid from membrane gangliosides of intact and ruptured chromaffin granules. Residual sialic acid was then measured to compare the availability of gangliosides on the outer and inner surfaces of the membrane. Measurement of protein sialic acid served as a control since these residues are known to be on the inner surface of the membrane. Prolonged digestion of broken membranes showed that maximally 75% of both lipid and protein-bound sialic acid residues are available to neuraminidase. Prolonged digestion of intact granules produced no measureable loss of sialic acid from either protein or lipid fractions. Comparison of the thin-layer chromatograms of gangliosides extracted from digested and undigested membranes showed no preferential digestion of any component. We conclude that at least 75% of the gangliosides are on the inner leaflet of the membrane and suggest that all of the gangliosides are so located.