IMMUNOCHEMICAL AND BIOCHEMICAL INVESTIGATION OF HEXOSAMINIDASE-S

Abstract

Hexosaminidase S (HEX S), the residual isozyme found in tissues and body fluids of children with the O variant of GM2 gangliosidosis, was purified from tissue of variant individuals and biochemically and immunochemically characterized. This enzyme has an apparent MW of 103,000 with an isoelectric point of 4.2, is heat labile to the same extent as HEX A, and loses most of its activity following heating for 30 min at 50.degree. C. HEX S reacts immunologically with the antisera against either HEX A or B, but the reaction is considerably stronger with the anti-A serum or with antibody preparations which react exclusively with the A isozyme. Results obtained by a radioimmunoassay using the various antisera indicated that there is no antigenically cross reacting material which lacks enzymatic activity in the variant tissues. These findings are in accord with a suggested molecular structure of 2 subunits, each composed of 2 .alpha. chains (.alpha.2.alpha.2) for HEX S; .alpha. and .beta. chains also apparently have some structural similarity which is manifested in antigenic cross-reactivity.