Steady-state current-voltage characteristics of amino acid transport in rhizoid cells of Riccia fluitans Is the carrier negatively charged? |
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Authors: | Hubert Felle |
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Institution: | Botanisches Institut I der Justus Liebig-Universität Giessen, Senckenbergstrasse 17-21, D-6300 Giessen F.R.G. |
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Abstract: | The amino acid transport across the plasmalemma of Riccia fluitans rhizoid cells has been further characterized by means of current-voltage ) analysis. On the basis of two cyclic transport models which include six different carrier states, the question is raised, whether the electrochemical pH-gradient drives a negatively charged carrier or a positively charged alanine-proton-carrier complex across the membrane. analysis shows that (1) the typical characteristic of l-alanine transport follows a sigmoid curve, (2) maximal accumulation of l-alanine within the cytoplasm is reached after about 1 hour, (3) the electrically accessible cytoplasmic l-alanine concentration is limited to about 20 mM, and (4) the steady-state saturation current depends directly on external l-alanine concentration. It is concluded that (a) these results are consistent with the predictions of the models for a negatively charged carrier, and (b) that the rate-limiting step involves the translocation of the ternary complex. |
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Keywords: | Current-voltage analysis Amino acid transport Alanine Carrier charge (R fluitans plasmalemma) |
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