Purification and Characterization of β-N-Acetylhexosaminidase I from Human Placenta

Abstract

β-N-Acetylhexosaminidase (hexosaminidase) I, which has an intermediate charge character between those of hexosaminidases A (αβ₂) and B((ββ)₂), was purified 1, 500-fold from human placenta by procedures including chromatographies on concanavalin A (Con A)-Sepharose and an immunoadsorbent column. The isolated hexosaminidase I was heat-stable, and antigenically cross-reactive to anti-β chain-IgG but not to anti-α chain-IgG. The results of substrate specificity experiments using ³H-labeled natural substrates indicated that the hexosaminidase I hydrolyzed Gb₄ Cer to Gb₃ Cer but not GM₂ to GM₃. The tryptic peptide map of the hexosaminidase I was similar to that of hexosaminidase B, though some differences were observed. The hexosaminidase I after treatment with neuraminidase or endo-β-N-acetylglucosaminidase H was partly converted to less acidic forms. Treatment of the hexosaminidase I with acid phosphatase did not change the charge character. Therefore hexosaminidase I is an acidic variant form of hexosaminidase B, possibly resulting from sialylation and the presence of phosphodiester bonds at the carbohydrate moiety.