The effect of pH on the kinetics of arylsulphatases A and B.
The effect of pH on the kinetics of rat liver arylsulphatases A and B is very similar and shows that two groups with pK values of 4.4-4.5 and 5.7-5.8 are important for enzyme activity. Substrate binding has no effect on the group with a pK of 4.4-4.5; however, the pK of the second group is shifted to 7.1-7.5 in the enzyme-substrate complex. An analysis of the effect of pH on the Ki for sulphate inhibition suggests that HSO4-is the true product. A model is proposed that involves the two ionizing groups identified in the present study in a concerted general acid-base-catalysed mechanism.
D002553:Cerebroside-Sulfatase / Q000378:metabolism*; D002803:Chondro-4-Sulfatase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D009578:Nitrobenzenes / Q000378:metabolism; D013429:Sulfatases / Q000378:metabolism*; D013431:Sulfates / Q000378:metabolism
D009578:Nitrobenzenes; D013431:Sulfates; C023379:4-nitrophenyl sulfate; D013429:Sulfatases; D002553:Cerebroside-Sulfatase; D002803:Chondro-4-Sulfatase