Role of unsaturated derivatives of spermidine as substrates for spermine synthase and in supporting growth of SV-3T3 cells

Synthetic unsaturated analogues of the natural polyamines were examined as possible substrates for spermine synthase and as replacements for spermidine in supporting the growth of SV-3T3 cells. It was found that N-(3-aminopropyl)-1,4-diamino-cis-but-2-ene [the cis isomer of the alkene analogue of spermidine] was a good substrate for spermine synthase, but that the trans isomer [N-(3-aminopropyl)-1,4-diamino-trans-but-2-ene] and the alkyne analogue [N-(3-aminopropyl)-1,4-diaminobut-2-yne] were not substrates. These results provide the first demonstration of stereospecificity in the spermine synthase reaction. All three of the unsaturated spermidine analogues described above and the cis-alkene analogue of spermine [N¹N⁴-bis-(3-aminopropyl)-1,4-diamino-cis-but-2-ene] were able to support the growth of SV-3T3 cells that were prevented from the endogenous synthesis of spermidine by treatment with α-difluoromethylornithine. Since N-(3-aminopropyl)-1,4-diamino-trans-but-2-ene] and N-(3-aminopropyl)-1,4-diaminobut-2-yne were not converted into a spermine derivative, it is apparent that this conversion is not needed for the stimulation of growth. However, since N¹N⁴bis-(3-aminopropyl)-1,4-diamino-cis-but-2-ene was also able to support growth and was not degraded to the spermidine derivative, it appears that either polyamine can be effective in this respect. All of the unsaturated analogues tested accumulated in the SV-3T3 cells to a much greater extent than spermidine itself. This indicates that these compounds are substrates for the polyamine transport system, but that they are less effective than the natural polyamines in the feedback regulation of this system.