a-Hydrazinoornithine is a potent inhibitor of ornithine decarboxylase (EC 18.104.22.168, l-ornithine carboxy-lyase) with Ki values for the enzyme from Escherichia coli and rat ventral prostate of 5 · 10-7 and 2·10-6 M, respectively. Inhibition of ornithine decarboxylase by a-hydrazinoornithine is relatively selective, since the drug is 1-2 orders of magnitude less potent in inhibiting other pyridoxal phosphate-dependent amino acid decarboxylases. Other hydrazino compounds examined are much less potent inhibitors of ornithine deacrboxylase than a-hydrazinoornithine. Inhibition by a-hydrazinoornithine is reversible and competitive with respect to substrate.
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