FIG. 5.

Double-reciprocal plots of [¹⁴C]putrescine uptake by E. coli B cells, in the presence or absence of various ethyl and benzyl analogues of spermine. The incubation mixture of cells was prepared as described in the legend to Fig. 4. The [¹⁴C]putrescine uptake was determined in the absence of analogues (●) or in the presence of 100 μM N¹,N¹²-bis(ethyl)spermine (□), N⁴,N⁹-bis(ethyl)spermine (▵), N¹-ethylspermine (○), and N⁴,N⁹-dibenzylspermine (■). Inset, detail of the kinetic plots at high concentrations of [¹⁴C]putrescine.