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

Here we report the determination of the activation energies of the plasma i soenzymes of beta-N-acetylhexosaminidase (Hex, EC 3.2.1.52), isolated by ch romatography in DEAE-cellulose, using the neutral chromogenic substrate 3,3 'dichlorophenylsulfonphthaleinyl-N-acytl-beta-D-glucosaminide. The activati on energy of mutated Hex A isoenzyme (E-a approximate to 71.5 kJ/mol) from a patient with GM2-gangliosidosis B1 variant, homozygote for the G533 -->A (Arg178His) mutation, was significantly higher than that of normal Hex A (E -a approximate to 41.8 kJ/mol) and analogous to that of Hex B isoenzyme (E- a approximate to 75.1 kJ/mol). The determination of this thermodynamic vari able of Hex in different biological specimens could allow for a straightfor ward biochemical characterisation of the GM2-gangliosidosis B1 variant. (C) 1999 Elsevier Science B.V. All rights reserved.