Mechanism of polyamine spermidine uptake by Xenopus laevis oocytes |
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Authors: | N A Khan V Quemener R Havouis J P Moulinoux |
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Affiliation: | Unité Fonctionnelle de Biologie Cellulaire, CNRS SDI, Faculté de Médecine, C.H.U. de Rennes, France. |
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Abstract: | In this study, the mechanisms of polyamine spermidine (Spd) uptake were investigated in Xenopus laevis oocytes. Spd uptake followed a sigmoidal kinetics with [S]90/[S]10 = 3 microM and Hill interaction coefficient (n) = 2. The order of magnitude of uptake and efflux was similar (t1/2 = 45 min). The equilibrium potential for Spd, calculated by Nenrst equation, was 90.78 mV. Free energy change for the uptake (delta G) was found to be 2.31 Kcal/mole of Spd. During efflux, Spd was not converted into putrescine or spermine. It seems that there are two types of Spd uptake pathways: Na(+)-dependent and Na(+)-independent since replacement of Na+ from incubation medium did not completely abolish the Spd uptake. The Na(+)-dependent component of Spd uptake was shared neither by system A nor by system ASC amino acids. |
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