The Action on Soluble Blood Group A Substances of an α-N-Acetylgalactosaminidase from Helix pomatia

An α-N-acetylgalactosaminidase obtained from the hepatopancreas of Helix pomatia and purified 300-fold was allowed to act on soluble blood group A substances from human ovarian cyst fluid and hog gastric mucosa. This treatment resulted in an almost complete loss of serological A specificity and an 8- to 16-fold enhancement of blood group H activity as measured by hemagglutination inhibition tests. N-Acetylgalactosamine was found to be released. This indicates that the enzyme destroys the serological A specificity by removing from the antigenic sites terminal N-acetylgalactosamine residues thereby exposing structures similar to those present in H substances. Quantitative determinations suggest an average number of 120 antigenic sites per molecule of human blood group A substance, each of them being composed of two N-acetylgalactosamine, one N-acetylglucosamine, two galactose, and two fucose residues.