Effects of temperature on the transport of galactose in human erythrocytes.

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Abstract
The transport of galactose in human erythrocytes was resolved recently into a mechanism which involves 2 asymmetric carriers operating in antiparallel fashion. The effects of temperature on this mediated transport system at 0-25.degree. C showed the following features. The Michaelis constants for zero-trans influx and efflux and for equilibrium-exchange efflux, did not vary with temperature. Arrhenius plots of the maximal velocities showed breaks between 3-15.degree. C with activation energies 2- to 3-fold larger below the break than above it. The relative contribution of the 2 types of carriers to the total transport rate is not affected by temperature. The kinetic properties of the prevalent type of carriers were analyzed in terms of the simple carrier model as formulated by Lieb and Stein. The relative concentration of the unloaded carrier at the inner interface of the membrane increased upon cooling. The free energy of translocation of the unloaded carrier and the change in entropy involved in this step were significantly larger in the low temperature range (0-5.degree. C) than in the higher range (15-25.degree. C). The results were discussed briefly in terms of possible lipid-protein interaction and physico-chemical nature of the erythrocyte membrane.

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