Abstract
Spermine is taken up by Ehrlich ascites tumour cells through a specific, saturable, temperature and energy-dependent transport system with a remarkably low affinity constant for spermine (around 1 microM). In the absence of a potassium ion gradient through the plasma membrane, spermine uptake remains saturable but the value of the Km for spermine is much higher (153 microM). Difluormethylornithine treatment (3 mM for 48h) induces significant increases in Vmax values (up to 9-fold) and changes in the Km values with scarce statistical significance. Among the biogenic amines tested, only spermidine and, partly, agmatine seem to share the same transport system with spermine. No difference is observed in the rate of spermine transport when assays are carried out in the presence of 50-fold excess of ornithine or calcium, or 100-fold excess of glutamine.
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