Turnover number of 3 sodium-hydrogen exchanger (NHE) isoforms calculated from Vmax, measured by fluorometry at 37°C

Range 459-742 sec^-1
Organism Chinese hamster
Reference Cavet ME, Akhter S, de Medina FS, Donowitz M, Tse CM. Na(+)/H(+) exchangers (NHE1-3) have similar turnover numbers but different percentages on the cell surface. Am J Physiol. 1999 Dec277(6 Pt 1):C1111-21. p. C1119 Table 2 Table - link PubMed ID10600762
Method A Chinese hamster lung fibroblast cell line (PS120) previously selected to lack all endogenous NHEs was stably transfected, using Lipofectin (GIBCO BRL), with human NHE1 or rabbit NHE2 or NHE3 cDNAs epitope tagged on the COOH termini with a previously described 11-amino acid epitope of vesicular stomatitis virus glycoprotein (VSVG) plus an 8-amino acid spacer (NHE1V, NHE2V, and NHE3V). Researchers then determined the turnover numbers of NHE1, NHE2, and NHE3 expressed in the same cell type (PS120) by correlating the Vmax (as measured by 22Na+ uptake kinetic studies and fluorometry) with the amount of NHE protein expressed at the cell surface.
Comments In the present study, all three NHE isoforms had a turnover rate of ~80–100 s^-1 when Na+ uptake was used to measure Vmax at 22°C (BNID 105479) and a turnover number of 459–742 s^-1 when fluorometry at 37°C was used. NHEs in lymphocytes (likely to be NHE1) have a high temperature coefficient (Q10) of 3.1 (Livne et al 1987, PMID 2832967). When this is taken into account, the estimated turnover number for NHE1 determined by fluorometry at 22°C is 142 s^-1, which is close to that measured by 22Na+ uptake (80 s^-1).
Entered by Uri M
ID 105481