A more sensitive assay procedure has been developed for the enzyme iduronate 2-sulphate sulphatase which is deficient in the Hunter syndrome. The substrate is the same as previously described by Lim et al. [1], O-(alpha-L-idopyranosyluronic acid 2-sulphate)-(1leads to 4)-2,5 anhydro-D-[3H-1]mannitol 6-sulphate, but, after incubation, it is separated from the product by ion-exchange chromatography on a micro-column of Dowex 1 x 2 (Cl-1) instead of high voltage electrophoresis or ECTEOLA cellulose chromatography. Since the blank correction is then much smaller, a shorter incubation time can be used and conversion of the substrate reduced from approximately 50% down to levels where complications resulting from substrate depletion and product inhibition are minimal. Using whole serum the apparent Km for the substrate is 0.2 mmol/l. With an incubation time of 20 min, sera from heterozygotes exhibited approximately 35% of the normal levels of iduronate 2-sulphate sulphatase (0.11-0.61, mean 0.34 nmol.h-1.mg-1 protein for carriers; 0.24-2.35, mean 0.94 nmol.h-1.mg-1 protein for 37 normal females). Serum analyses can thus be used to supplement those on hair roots in the detection of carriers of the Hunter syndrome.
Chromatography, Ion Exchange Clinical Enzyme Tests