Biochemical and immunochemical characterization of hexosaminidase P

Abstract

Hexosaminidase P [EC 3.2.1.30], the main isozyme of hexosaminidase in pregnancy serum, was isolated from a human placenta and purified 600- to 700-fold by a 2-step purification procedure: affinity chromatography on Sepharose-bound .epsilon.-aminocaproyl-N-acetylglucosylamine, followed by ion-exchange chromatography on DEAE-cellulose. The purified enzyme was subjected to biochemical and immunochemical analysis. Its catalytic property, i.e., kinetic behavior, is similar to that of the major isozymes of hexosaminidase, A and B. It differs from these isozymes in its electrophoretic mobility and in its apparent MW which is around 150,000 compared with 100,000 of the A and B isozymes. Immunochemical analysis indicates that the P isozyme is antigenically cross-reactive with both A and B isozymes, but it does not contain the A-specific antigenic determinants, and exhibits identical antigenic specificity to hexosaminidase B. Two possible structures are suggested that are compatible with the experimental data: a hexosaminidase B-like structure with higher extent of glycosylation; a hexamer of .beta. chain, possibly arranged as 3 .beta.2 subunits.