Studies of the purine analog associated modulation of human erythrocyte acid phosphatase activity.

The activity of the human erythrocyte acid phosphatase is modulated by a series of structural analogs of purine. The unsubstituted purine base does not affect the enzyme activity. Addition of a substituent at the number six position usually generates an analog which activates the enzyme while similar substitutions at the two position usually generate an inhibitor. Pyrimidines are generally ineffective as modulators while several modifications of the imidazole ring of the purine analogs do not abolish the modulator activity of the purine analog. The level of response to all active analogs is isozyme specific. Differences in apparent relative affinities among the modulators are noted. The modulators with a positive effect on enzyme activity, are effective in the presence of methanol which is more effective than H2O as a phosphate acceptor. These analogs act by enhancing the rate of transfer of phosphate to H2O, while decreasing the rate of transfer to methanol. The results suggest that the purine analogs may act by altering the rate of hydrolysis of the phosphoenzyme intermediate by H2O or may change the rate-limiting step in the catalytic mechanism.