"Critical" turnover number in red cell membrane for sulfate

Range ~7X10^6 ions/cell/sec
Organism Human Homo sapiens
Reference Gasbjerg PK, Knauf PA, Brahm J. Kinetics of bicarbonate transport in human red blood cell membranes at body temperature. J Gen Physiol. 1996 Dec108(6):565-75. p.571 right column bottom paragraphPubMed ID8972394
Primary Source Glibowicka, M., B. Winckler, N. Aranfbar, M. Schuster, H. Hanssum, H. Rfiterjans, and H. Passow. 1988. Temperature dependence of anion transport in the human red blood ceil. Biochim. Biophys. Acta. 946: 345-358.PubMed ID3207750
Method "On the basis of studies of chloride transport mainly at 0°C, the "ping-pong model" for anion exchange was proposed (Gunn and Frohlich, 1979 Frohlich and Gunn, 1986). According to this model, a transport site in the protein, unloaded or loaded with an anion, may either face the internal or the external compartment."
Comments "When the Arrhenius plots for Cl-, Br-, and F- were fitted to two intersecting regression lines, the "break" in the lines occurred at different temperatures for Cl- (15°C) and Br- and F- (23-25°C), but at the same "critical" turnover number of ~4×10^9 ions/cell/sec (Brahm, 1977 Wieth and Brahm, 1985). The fact that the break occurs at different temperatures for different anions indicates that the nonlinear temperature dependence is not related to a phase transition in the membrane, which would occur at the same temperature regardless of the anion substrate. If two straight lines are used to fit the Arrhenius plot for HCO3- transport (Fig. 3), they intersect around 13°C. Thus, for monovalent anions, the break temperature ranges from 13 to 25°C, supporting the concept that the nonlinear temperature dependence of anion transport is not related to a phase transition in the membrane. The turnover number for HCO3- transport at 13°C is ~4×10^9 ions/cell/sec, similar to the critical turnover number for Cl-, Br-, and F-. Ions such as iodide, salicylate, and thiocyanate, which never reach the critical turnover number, show a constant apparent activation energy (Dalmark and Wieth, 1972). The divalent anion sulfate showed a decrease in the apparent Arrhenius activation energy when temperature is raised above 30°C (primary source), but the critical turnover number for sulfate was only ~7X10^6 ions/cell/sec, 500-600 times lower than that for chloride."
Entered by Uri M
ID 110858