The products of pronase digestion of purified blood group-specific glycoproteins.

Purified blood group-specific glycoproteins from ovarian cyst fluids were digested with pronase. The glycoproteins, which had dissimilar amino acid compositions, lost varying amounts of amino acids to leave pronase-resistant cores with very similar compositions. The resistant materials, which were glycoproteins with blood group activities similar to those of the starting materials, contained all of the original carbohydrate. Thus the peptide material removed by pronase action must originate from regions of the macromolecule devoid of sugar. These results confirm previous suggestions that two types of region exist in blood group substances. Threonine, serine and proline accounted for about two thirds of the amino acids present in the pronase-resistant regions. The aromatic and the sulphur-containing amino acids were virtually eliminated by the enzyme treatment. The pronase products of the B, H and Le(a) substances had a near 1:1 ratio of galactosamine to hydroxyamino acids. Similar enzyme resistant materials were obtained when the blood group substances were digested with an insoluble derivative of pronase. On gel filtration the enzyme-resistant materials from different blood group substances had, unlike the parent substances, similar elution profiles and peak elution volumes. Ultracentrifugal examination of one of the pronase-resistant materials indicated that it had a molecular weight of 0.7 x l0(6). Alkaline degradation showed that the enzyme-treated substances had a higher and more uniform degree of O-glycosidic substitution of threonine and serine by carbohydrate chains than did the starting materials.