An investigation into the feasibility of using azide-insensitive ATPase and ConA as yeast plasma membrane markers.

Cytochemical localization of Concanavalin A binding sites in protoplasts of Candida tropicalis, investigated with glycosylated-ferritin and electron microscopy, showed that the lectin was specifically bound to the external protoplast surface. Thus, the plasma membranes have been labelled with 125I-Concanavalin A and followed through the isolation procedure. Relative distribution of 125I-radioactivity and azide-insensitive ATPase activity in the obtained fractions, suggested that this enzyme was an equivocal plasma membrane marker. Despite the presence of internal Concanavalin A binding sites, Concanavalin A could be used unambiguously as an exogenous plasma membrane marker of intact protoplasts.