The MzVariety of the St(a+) Phenotype — a Variant of Glycophorin A Exhibiting a Deletion

The NeuNAc level of erythrocyte membranes from two related donors exhibiting the Mz variety of St(a+) phenotype within the MNSs blood group system was found to be decreased by about 16%. The quantity of glycophorin A was decreased by about 38%, whereas that of glycophorin B was not significantly different from normal. Mz erythrocyte membranes were also found to contain an abnormal component (molar ratio to glycophorin A about 0.89:1.0) with an apparent molecular mass of about 24,000 Da. Immunoblotting experiments and amino-acid sequence analysis revealed that the novel component (and glycophorin A in one of the donors) carries blood group M activity. Blood group N activity was demonstrable for glycophorin A and glycophorin B from both donors. Amino-acid sequence analysis of chymotryptic, tryptic and cyanogen bromide peptides demonstrated that the novel molecule exhibits the typical structure of a Sta-active molecule. However, since it exhibits blood group M activity, it appears to represent a variant of glycophorin A lacking the residues 27-58 (encoded by exon three of the glycophorin A gene) rather than a glycophorin B-glycophorin A-hybrid molecule of the anti-Lepore type. Since one of the Mz heterozygotes was found to exhibit both M- and N activity on glycophorin A, the Mz gene complex appears to encode a blood group N-active glycophorin A apart from the novel component and a blood group s-active glycophorin B, although the level of glycophorin A in the erythrocyte membranes is decreased by about half.(ABSTRACT TRUNCATED AT 250 WORDS)