Differential inhibition of mammalian aminopropyltransferase activities

Rat ventral prostate spermine synthetase was inhibited by 5′-methylthioadenosine and by S-adenosylhomocysteine at concentrations which did not inhibit spermidine synthetase from the same tissue. S-Adenosylethionine inhibited both enzymes to an equal extent. These aminopropyltransferases were also inhibited by diamines not normally present in mammalian cells. All the α,ω-diamines with 3 to 12 C atoms had inhibitory activity, but 1,3-diaminopropane and 1,5-diaminopentane were most active. Spermine synthetase was more sensitive than spermidine synthetase to the effects of these diamines. These results suggest that the relative rates of spermidine and spermine formation in,vivo might be affected by the intracellular concentration of nucleosides such as S-adenosylhomocysteine. They also raise the possibility that these rates of synthesis could be selectively affected by administration of one or the other of these inhibitors.