Importance of SH groups in catalysis by bovine brain acid phosphatase

The rate of inactivation of acid phosphatase (EC 3.1.3.2) from bovine brain by dithiobis-(2-nitrobenzoic acid) (Nbs2) is identical to the rate of titration of one of the two SH groups of this enzyme. The rate of inactivation of the enzyme by Nbs2 is pH dependent and, at 300 mM NaCl, can be described by the reaction of a single SH group of pK 8.4. At low ionic strength the pK determined from the k inactivation vs. pH profile is 7.7 and the results deviate markedly from the predicted values at pH values less than or equal to 6. The decrease of V upon addition of salts is paralleled by the decrease of inactivation rate by Nbs2. The relevance of SH groups in catalysis by bovine brain acid phosphatase is discussed in terms of these data.