Acetylation of spermidine in polyamine catabolism.

Treatment with thioacetamide (150 mg/kg) was used to enhance polyamine metabolism in rat liver. The increased uptake and catabolism of [14C]spermine and the changes of putrescine, spermidine and spermine concentrations indicated enhanced polyamine turnover rates. The increase of hepatic putrescine concentration was accompanied by an increase of monoacetylputrescine and N1-monoacetylspermidine concentration. In control animals, the latter compound was below detection levels. Thioacetamide treatment also enhanced putrescine excretion, which again was concomitant with an increased excretion of N1-acetylspermidine. The close time-dependent correlation between induced putrescine formation and enhanced formation of N1-acetylspermidine at a time when liver spermidine and spermine concentrations are not changed, favors the notion that acetylation is an essential step in polyamine degradation and elimination. The increase of polyamine oxidase and decrease of acetylpolyamine deacetylase activities in the liver of thioacetamide-treated rats is in line with an increased polyamine turnover, but these enzymes, although essential, are not rate-limiting in the catabolic reactions.