The reaction of alkylating agents with cyclic 3',5'-nucleotide phosphodiesterase

The reaction of anti-tumour alkylating agents with beef heart cyclic nucleotide phosphodiesterase (adenosine 3',5'-monophosphate phosphohydrolase, EC 3.1.4.c) has been investigated. This enzyme exists in two forms differing in their Michaelis-Menten K_m values. Chlorambucil [p-(di-2-chloroethylamino)-phenyl-butyric acid] inhibits the form of the enzyme with a low K_m value with a velocity constant for inactivation three times that for inhibition of the high K_m form. While the monofunctional N-ethyl analogue of chlorambucil is ineffective as an inhibitor of either form of the enzyme, iodoacetate inhibits both forms, though the velocity constant for inactivation of each form is much less than that for chlorambucil. Also the rate of inactivation of each form does not significantly differ. A cross-linking mechanism for the inactivation of regulatory enzymes is proposed.