Summary
InNitella, current-voltage relationships were measured at different temperatures ranging from 5 to 25°C. Sets of theseI/V curves were subject to curve fitting on the basis of a cyclic reaction scheme (Class I model). Different hypotheses of the mode of action of temperature on theI/V curve were tested, including changes in reaction constants in the transport cycle and deactivation of transport molecules. It was found that models assuming an influence of temperature on pairs of rate constants of the transport cycle gave very bad fits. Good fits were obtained with models implying that temperature influences the number of active transporters. The lazy-state model (the exchange of an inactive state with a stateN 3 in the transport cycle is influenced by temperature) gave a slightly better fit than the assumption of an unspecific inactivation (independent of the state of the transport molecule). According to the lazy-state analysis, the inactive state is kinetically closer toN o , the state in which the transport molecule is open to the outside substrate than toN i , the state in which it is open to the inside substrate. The two inactivation models imply that temperature does not act directly on the properties of the plasmamembrane, but that temperature-sensitive metabolic processes in the cell send signals which control the activation and deactivation of the transporter.
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Hansen, UP., Fisahn, J. I/V-Curve studies of the control of a K+ transporter inNitella by temperature. J. Membrain Biol. 98, 1–13 (1987). https://doi.org/10.1007/BF01871041
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DOI: https://doi.org/10.1007/BF01871041