Binding sites for horseradish peroxidase on the cell surface

Summary The cytochemical reaction for surface-bound horseradish peroxidase (HRP) on cultured HeLa cells, GH₃ cells, and isolated rat liver cells was suppressed by 30 M monosialoganglioside, by 30 M trisialoganglioside, or by 5 mM CMP-neurminic acid. The reaction was also suppressed by 10 mM chitotriose or by 10 mM UDP-galactose, a galactose acceptor and donor, respectively, for galactosyltransferase. The addition of 2 mM Mn²⁺ to the incubation medium with HRP suppressed the reaction for surfacebound HRP, and the addition of 10–20 mM Ca²⁺ intensified the reaction. The addition of 2 mM Zn²⁺ caused less inhibition than that of 2 mM Mn²⁺, and the addition of 2 mM Co²⁺ caused either a slight inhibition, or no inhibition. These observations support the hypothesis that HRP may be bound to a glycosyltransferase at the cell surface.