Thermodynamic characterisation of the mutated isoenzyme A of β- N-acetylhexosaminidase in GM2-gangliosidosis B1 variant

Abstract

Here we report the determination of the activation energies of the plasma isoenzymes of β- N-acetylhexosaminidase (Hex, EC 3.2.1.52), isolated by chromatography in DEAE-cellulose, using the neutral chromogenic substrate 3,3′dichlorophenylsulfonphthaleinyl- N-acetyl-β- d-glucosaminide. The activation energy of mutated Hex A isoenzyme ( E a≈71.5 kJ/mol) from a patient with GM2-gangliosidosis B1 variant, homozygote for the G533→A (Argl78His) mutation, was significantly higher than that of normal Hex A ( E a≈41.8 kJ/mol) and analogous to that of Hex B isoenzyme ( E a≈75.1 kJ/mol). The determination of this thermodynamic variable of Hex in different biological specimens could allow for a straightforward biochemical characterisation of the GM2-gangliosidosis B1 variant.