Studies on the human blood group P system: an existence of UDP-Gal:lactosylceramide alpha 1----4 galactosyltransferase in the small p type cells.

Human red blood cells and other tissues with the rare small p type lack all P antigens, and are assumed to be missing key glycosyltransferases in the synthetic pathway of P antigens. Galactosyltransferase activities of the P1 and small p cell extracts were measured using lactosylceramide and GlcNAc as galactose acceptors. The two transferase activities of the small p lymphoblastoid cell extract were comparable to that of the P1 cell extract. The anomeric configuration of the galactosylated lactosylceramide was established by digestion with alpha- and beta-galactosidases, by identification of methylated products, and by staining with the monoclonal antibody against globotriaosyl ceramide (Pk antigen). The results indicate that UDP-Gal:LacCer alpha 1----4 Gal transferase, which produces the Pk antigen from the precursor LacCer, exists in the small p cells. However, intact small p cells could not produce the Pk antigen, and, instead, LacCer was accumulated in the cells. The Pk enzyme appears to be not functional in the small p cells in vivo.