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Structural specificity of the spermidine requirement of an Escherichia coli auxotroph

A homologous series of spermidine analogs was synthesized with the general structure NH3+ (CH2)nNH2+(CH2)3NH3+, where spermidine has n = 4. The influence of these compounds on growth and on the syntheses of protein and messenger ribonucleic acid was examined in a spermidine auxotroph of Escherichia coli. All of the homologs tested were taken up by the cells to an intracellular level equivalent to the level of spermidine which gives optimal growth. With increasing chain length of the homologs, there was reduced ability to stimulate growth. The homologs with n = 7 and n = 8 were essentially inactive. A similar specificity was observed when the ability of the homologs to restore the rates of protein and messenger ribonucleic acid chain elongation was compared to that of spermidine. These results suggest that a definite spatial arrangement of the amino groups of spermidine is required for productive interaction at its intracellular site(s) of action.