Catalytic and immunochemical properties of arylsulphatase A from urine, modified by potassium ferrate

Arylsulphatase A (EC 3.1.6.1.) from urine was inactivated with potassium ferrate, a strong oxidizing agent. The inhibition could be prevented by competitive inhibitors, tetraborate and orthophosphate. Tetraborate which was shown to be a powerful competitive inhibitor (determined Ki = 4 X 10(-5) M) gave more efficient protection. The partially inactivated enzyme exhibited a Km value similar to that of the unmodified arylsulphatase A, and its Vmax decreased in proportion to the loss of enzymatic activity. The partially modified enzyme did not lose its ability to catalyse hydrolysis of p-nitrocatechol sulphate according to the "anomalous kinetics" exhibited towards this substrate and characteristic for arylsulphatase A. The immunochemical properties of arylsulphatase A either fully or partially inactivated were similar to those of the native enzyme. The results allow to conclude that ferrate reacts with arylsulphatase A in its active site. Thus ferrate seems to be a very sensitive probe for amino acid residues essential for catalytic activity of arylsulphatase A.