"Critical" turnover number in red cell membrane for Cl- (15°C), Br- and F- (23-25°C) and HCO3- (13°C)

Range ~4X10^9 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 2nd paragraphPubMed ID8972394
Primary Source Brahm,J. 1977. Temperature-dependent changes of chloride transport kinetics in human red cells.J. Gen. Physiol. 70: 283-306. & Wieth, J.O., and J. Brahm. 1985. Cellular anion exchange. In The Kidney: Physiology and Pathology. D.W. Seldin and G. Giebisch, editors. Raven Press, New York. 49-89.PubMed ID19556
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 (primary sources). 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-."
Entered by Uri M
ID 110857