Specific Determination of N‐Acetyl‐β‐d‐hexosaminidase Isozymes A and B by Radioimmunoassay and Radial Immunodiffusion

The two major isozymes of N‐acetylhexosaminidase, namely hexosaminidases A and B were quantitatively determined in tissues and biological fluids of both normal individuals and Tay‐Sachs patients. The determination was carried out by two sensitive immunoassays: radial immunodiffusion, using chromogenic substrate, and radioimmunoassay, which were developed in this study. For this pupose we used either a cross‐reactive antiserum which reacts to a similar extent with both isozymes, or an antiserum reacting exclusively with hexosaminidase A (obtained by selective immunoadsorption). This enabled the quantitisation of the two isozymes separately, or in the presence of each other, in purified enzyme preparations or in tissue homogenates, affording a direct positive determination of hexosaminidase A. The results demonstrated that normal tissues contain the two isozymes in comparable amounts, whereas tissues of Tay‐Sachs patients lack hexosaminidase A or any material which carries the A‐specific antigenic determinants. The possible applications of these assays and their potential use in diagnosis are discussed.