Characterization of human red cell Rh (rhesus-)specific polypeptides by limited proteolysis.

Human red cells of various Rh phenotypes were surface-labelled with 125I and the Rh-specific labelled polypeptides were isolated by preparative SDS-PAGE. The polypeptides were subjected to limited proteolysis and the resulting fragments were analysed by SDS-PAGE and autoradiography. Chymotryptic peptide maps of proteins obtained from Rh(D)-positive and -negative types appeared completely identical, whereas tryptic peptide maps revealed a difference: a fragment of Mr 17,500 was associated with the Rh(D) antigen, and one of Mr 19,000 with the Rh(C/c,E/e) antigens. Treatment of Rh polypeptides with carboxypeptidase Y prior to tryptic digestion resulted in a shift of nearly all tryptic fragments, including a fragment of Mr 8,000, indicating that the surface label was incorporated into the C-terminal part of the molecule.