Evidence for two different active sites on human beta-hexosaminidase A. Interaction of GM2 activator protein with beta-hexosaminidase A.
Competition experiments were carried out on the hydrolysis of different substrates by beta-hexosaminidase A isolated from human liver. The results show that ganglioside GM2 in the presence of the GM2 activator protein and a new synthetic substrate, 4-methylumbelliferyl-beta-N-acetylglucosaminide 6-sulfate, are hydrolyzed at the same active site on the alpha subunit of beta-hexosaminidase A, whereas 4-methylumbelliferyl-beta-N-acetylglucosaminide is degraded predominantly by a different active site on the beta-subunit. This finding provides for the first time a possible molecular basis for the observation that, in variant B1 of the GM2 gangliosidoses, beta-hexosaminidase A has lost its activity toward GM2 ganglioside and the sulfated artificial substrate while being still able to hydrolyze the unsulfated artificial substrate at a normal rate. Furthermore, the finding that the GM2 activator protein inhibits the degradation of the sulfated substrate by beta-hexosaminidases A and S indicates that the alpha subunit common to both isoenzymes might provide a binding site for the activator protein.
Kytzia
H J
HJ
Sandhoff
K
K
D001665:Binding Sites; D049289:G(M2) Activator Protein; D005678:G(M2) Ganglioside / Q000378:metabolism*; D005732:Gangliosides / Q000378:metabolism*; D006596:Hexosaminidases / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D046911:Macromolecular Substances; D011506:Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D001619:beta-N-Acetylhexosaminidases
D049289:G(M2) Activator Protein; D005732:Gangliosides; D046911:Macromolecular Substances; D011506:Proteins; D005678:G(M2) Ganglioside; D006596:Hexosaminidases; D001619:beta-N-Acetylhexosaminidases