The distribution of Concanavalin A receptor sites on the membrane of chromaffin granules

The distribution of concanavalin A (con A) receptor sites on the membranes of chromaffin granules has been investigated by binding studies using 125I-labelled con A and by electron-microscope studies using ferritin-labelled con A. In both experiments con A was observed to bind to chromaffin granule membranes but not to intact granules. The ferritin-con A particles bind to only one of the two possible surfaces of the chromaffin granule membranes. These results are in agreement with previous observations concerning the asymmetric distribution of saccharide residues on the surfaces of a number of different plasma membranes. They suggest that for the intracellular membrane of the chromaffin granule the saccharide sites, like those in plasma membranes, are not exposed to the cell cytoplasm. Further work is necessary to establish whether these sites are on the inner surface of the membrane or whether they are unmasked during the conversion of granules to membrane ghosts.