Hydrolysis of Tay-Sachs Ganglioside by β-Hexosaminidase A of Human Liver and Urine

A crude β-hexosaminidase fraction prepared by (NH4)2SO4 fractionation of human liver extract or urine was found to convert Tay-Sachs ganglioside, GalNAcβ1 → 4(NANα2 → 3)Galβ1 → 4Glc → ceramide (Gm2) into NANα2 → 3Galβ1 → 4 Glc → ceramide (Gm3). After separation of hexosaminidase A and B by DEAE-cellulose chromatography, only freshly prepared β-hexosaminidase A hydrolyzed Gm2 although both forms were still active toward p-nitrophenyl-β-d-N-acetylglucosaminide. A heat-stable, nondialyzable preparation obtained from the crude β-hexosaminidase fraction of human liver was found to stimulate the hydrolysis of Gm2 by β-hexosaminidase A but not B isolated from both sources. Upon aging, β-hexosaminidase A would only hydrolyze Gm2 in the presence of the heat-stable preparation. Extensive purification as well as aging tended to reduce the capacity of β-hexosaminidase A to hydrolyze Gm2 even in the presence of the heat-stable preparation. Our results explain why β-hexosaminidase A has been previously reported by other investigators to hydrolyze Gm2 only with great difficulty. Our results also relate the inordinate storage of Gm2 to the absence of β-hexosaminidase A in the classical form of Tay-Sachs disease.