FORSSMAN HAPTEN N‐ACETYL‐α‐D‐GALACTOSAMINIDASE IN RAT BRAIN AND KIDNEY1

Abstract —Forssman hapten (N‐acetyl‐α‐galactosaminosyl‐N‐acetyl‐β‐galactosaminosyl‐α‐galactosyl‐β‐galactosyl‐glucosylceramide), prepared from sheep erythrocytes was specifically labelled with tritium at the terminal N‐acetyl‐α‐galactosamine moiety by the galactose oxidase‐sodium [3H]borohydride method. Activities to cleave the terminal N‐acetyl‐α‐galactosamine from Forssman hapten were detected in the high‐speed supernatant of the frozen‐thawed and sonicated crude mitochondrial fraction from adult rat brain and kidney. The optimal pH of the reaction was approximately 4·4. The reaction was linear for at least 1 h for the kidney enzyme and up to 3 h for the brain enzyme. Taurocholate was required for the activity. The optimal concentration was 1·5‐2 mg/ml. Several other detergents and bile salts tested could not replace taurocholate. The apparent Km of the brain and kidney enzymes were 1·0×10−4M and 3·5×10−4m, respectively. During development, Forssman hapten‐cleaving activities of both brain and kidney gradually declined in specific activity as the animal matured. These changes were similar to those of nonspecific p‐nitrophenyl N‐acetyl‐α‐galactosaminidase. Several rat organs examined all showed detectable activities to cleave Forssman hapten.