Lysosomal A, B, and S Isozymes
Functional lysosomal β-hexosaminidase enzymes are dimeric in structure. Three isozymes are produced through the combination of α and β subunits to form any one of three active dimers:
| hexosaminidase isozyme |
subunit composition | function |
|---|---|---|
| A | α/β heterodimer | only isozyme that can hydrolyze GM2 ganglioside in vivo |
| B | β/β homodimer | exists in tissues but no known physiological function |
| S | α/α homodimer | exists in tissues but no known physiological function |
The α and β subunits are encoded by separate genes, HEXA and HEXB respectively. Beta-hexosaminidase and the cofactor GM2 activator protein catalyze the degradation of the GM2 gangliosides and other molecules containing terminal N-acetyl hexosamines. Gene mutations in HEXB often result in Sandhoff disease; whereas, mutations in HEXA decrease the hydrolysis of GM2 gangliosides, which is the main cause of Tay-Sachs disease.
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Read more about this topic: Hexosaminidase, Isozymes and Genes