| Range |
at pH=6.5 48: at pH=8.5 89,000 min^-1
|
| Organism |
Bacteria Escherichia coli |
| Reference |
Taglicht D, Padan E, Schuldiner S. Overproduction and purification of a functional Na+/H+ antiporter coded by nhaA (ant) from Escherichia coli. J Biol Chem. 1991 Jun 15 266(17):11289-94. p.11294 left column top paragraphPubMed ID1645730
|
| Comments |
p.11293 right column bottom paragraph:” The Vmax measured for the ?pH-driven uptake of sodium is 3250 nmol/min/mg of protein. This value is 100 times higher than values obtained previously for the Na+/H+ antiporter activity of membranes derived from the wild type E.coli (30 nmol/min/mg Goldberg et al. (1987)), as expected from the degree of overproduction and purification. On the other hand, the downhill efflux rates are much higher, increasing from 1.2 µmol/min/mg at pH 6.5 to 2.2 mmol/min/mg at pH 8.5. These values correspond to turnover numbers from 48 min^-1 to 89,000 min^-1, respectively. This high turnover number for an ion-coupled transport system is one of the highest reported thus far and is only 10 times lower than the turnover number of the erythrocyte anion exchanger (Cabantchik, 1990). Whether the difference in rate of the two catalytic modes is due to an effect of pH or to the presence of another rate-limiting step is still to be elucidated.” |
| Entered by |
Uri M |
| ID |
111777 |