FIG. 4.

Double-reciprocal plots of [¹⁴C]spermine uptake by E. coli B cells, in the presence or absence of various alkyl and benzyl analogues of spermine. E. coli B cells grown in supplemented M9 medium were washed and suspended in buffer A to yield a protein concentration equal to 0.1 mg/ml. The [¹⁴C]spermine 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 (□). Each point represents the mean value of four individual measurements.