Inactivation of low-Km rat liver mitochondrial aldehyde dehydrogenase by cyanamide in vitro. A catalase-mediated reaction.

The inactivation of the affinity chromatography purified low-Km rat liver mitochondrial aldehyde dehydrogenase (ALDH)--free of catalase activity--by the alcohol sensitizing agent cyanamide was studied in vitro. This ALDH-purified preparation was not susceptible to cyanamide inactivation at concentrations up to 2.5 mM. On the other hand, ALDH activity appears to be irreversibly inhibited when the incubation mixture contained ALDH, catalase, NAD+ and cyanamide. Influence of catalase, NAD+ and cyanamide concentrations in the incubation mixtures on the ALDH activity were also established. The time course of the concentration of cyanamide in an incubation mixture when ALDH activity was inhibited by cyanamide in the presence of catalase and NAD+, was evaluated by HPLC. No disappearance of cyanamide was observed for a period of time up to 24 hr. This result suggests that no metabolic conversion of cyanamide to an active inhibitory form takes place, as has been suggested recently.