Effects of ethyl and benzyl analogues of spermine on Escherichia coli peptidyltransferase activity, polyamine transport, and cellular growth

Various ethyl and benzyl spermine analogues, including the anticancer agent N-1,N-12-bis(ethyl)spermine, were studied for their ability to affect the growth of cultured Escherichia coli cells, to inhibit [H-3] putrescine and [H-3] spermine uptake into cells, and to modulate the peptidyltransferase a ctivity (EC 2. 3. 2. 12). Relative to other cell lines, growth of E. coli w as uniquely insensitive to these analogues, Nevertheless, these analogues c onferred similar modulation of in vitro protein synthesis and inhibition of [H-3]putrescine and [H-3]spermine uptake, as is seen in other cell types. Thus, both ethyl and benzyl analogues of spermine not only promote the form ation and stabilization of the initiator ribosomal ternary complex, but the y also have a sparing effect on the Mg2+ requirements. Also, in a complete cell-free protein-synthesizing system, these analogues at low concentration s stimulated peptide bond formation, whereas at higher concentrations, they inhibited the reaction. The ranking order for stimulation of peptide-bond formation by the analogues was N-4,N-9-dibenzylspermine > N-4,N-9-bis(ethyl )spermine congruent to N-1-ethylspermine > N-1,N-12-bis(ethyl)spermine, whe reas the order of analogue potency regarding the inhibitory effect was inve rted, with inhibition constant values of 10, 3.1, 1.5, and 0.98 mu M, respe ctively. Although the above analogues failed to interact,vith the putrescin e-specific uptake system, they exhibited high affinity for the polyamine up take system encoded by the potABCD operon. Despite this fact, none of the a nalogues could be internalized by the polyamine transport system, and there fore they could not influence the intracellular polyamine pools and growth of E. coli cells.