Hexosamines Hexosaminidase

This enzyme [EC 3.2.1.52] (also known as /3-A-acetylhex-osaminidase, )3-hexosaminidase, hexosaminidase, and N-acetyl-/3-glucosaminidase) catalyzes the hydrolysis of terminal nonreducing A-acetyl-o-hexosamine residues in... 

Beta-N-acetylhexosaminldase. Beta-hexosaminidase. Hexosaminidase. N-acetyl-beta-glucosaminidase. 3.2.1.52 Hydrolysis of terminal non-reducing N-acetyl-D-hexosamine residues in N-acetyl-beta-D-hexosaminides. 

As indicated earlier, tlie rarer hexosamines are characteristically microbial products which are noii-A -acylated, and there are observations which suggest that the resultant positive electric charge may be necessary for the antibiotic activity of these substances (Polglase, 1965 Modolell and Davis, 1969). It is likely that this electric charge would make the glycosides extremely resistant to acid hydrolysis (Kent and Whitehouse, 1955), and would almost certainly preclude their hydrolysis by known hexosaminidases. 

The activity of this enzyme was found to be at equivalent levels in both normal and Tay-Sachs tissues. Aberrant hexosaminidase activities have been reported in Tay-Sachs tissues. Elevated levels of activity toward synthetic nitrophenyl hexosaminosides as substrates has been reported in Tay-Sachs cerebral tissues (Okada and O Brien, 1969). Disc gel electrophoresis of normal tissues reveals the presence of two hexosaminidase activities, while in Tay-Sachs tissues only one is found (Okada and O Brien, 1969). A Tay-Sachs ganglioside specifically labeled in the N.ANA and A -acetyl galactasamine residues has been prepared by the in vivo administration of A -acetyl galactosamine- H into young rats. Employing this material as substrate, no release of hexosamine was detected w ith Tay-Sachs tissue, while detectable amounts were found with... 

Sandhoff disease Panethnic but otherwise virtually indistinguishable from Tay-Sachs disease GM2 ganglioside, asialo-GM2 ganglioside, globoside Glycoprotein with terminal P-hexosamine P-Hexosaminidase A and B... 

These analytical findings can be explained on the bases of the enzymatic defect in Sandhoff disease. P-Hexosaminidase p subunit is genetically defective in this disorder. Therefore, both hexosaminidase A (aP) and B (PP) isozymes are equally deficient ( total hexosaminidase deficiency ). While hexosaminidase S (aa) does exist, it is catalytically inactive toward natural substrates. The end result is the inability to degrade all natural sphingolipid and glycoprotein substrates beyond the stage where the next step is removal of a hexosamine residue. 

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