STUDIES ON THE MODE OF ACTION OF DIPHTHERIA TOXIN

Abstract

Inhibition of soluble transferase II activity in cell-free systems by diphtheria toxin and NAD can be prevented or reversed in the presence of a sufficient concentration of nicotinamide. Quantitative studies on inhibition of peptide bond formation in cell-free extracts by toxin and NAD have indicated that two successive reversible reactions are involved. First, toxin and NAD interact mole for mole to form a relatively dissociable complex. This toxin-NAD complex then reacts with transferase II to form an enzymatically inactive product that is but slightly dissociated. In the presence of sufficient nicotinamide, however, the latter complex can be broken down to yield active transferase II once more.