Modification of the catalytic and regulatory properties of beef heart AMP-deaminase by DTNB treatment.

In beef heart AMP-deaminase (EC 3.5.4.6.), 7 SH-groups out of 26 half-cysteine residues in the protein molecule have been shown to be accessible to alkylation by DTNB in the absence of ATP. The addition of ATP showed that only 6 SH-groups were accessible. DTNB-modified enzyme showed about 30% of the native catalytic activity but no sensitivity to the ATP-activating effect. Almost full reactivation of the modified enzyme and the restoration of the activatory effect of ATP could be achieved by exhaustive dialysis against mercaptoethanol.