KINETICS AND STOICHIOMETRY OF A PROTON MYO-INOSITOL COTRANSPORTER/

Citation
Em. Klamo et al., KINETICS AND STOICHIOMETRY OF A PROTON MYO-INOSITOL COTRANSPORTER/, The Journal of biological chemistry, 271(25), 1996, pp. 14937-14943
Citations number
20
Categorie Soggetti
Biology
ISSN journal
00219258
Volume
271
Issue
25
Year of publication
1996
Pages
14937 - 14943
Database
ISI
SICI code
0021-9258(1996)271:25<14937:KASOAP>2.0.ZU;2-L
Abstract
Voltage clamp recording was used to measure steady-state and presteady state currents mediated by a myoinositol transporter cloned from Leis hmania donovani and expressed in Xenopus oocytes, Application of myoin ositol resulted in inward currents, which did not require external sod ium and which were increased by increasing the extracellular proton co ncentration and by membrane hyperpolarization, Alkalinization of the e xtracellular space occurred concomitantly with myo-inositol influx. Co rrelation of membrane currents with radiolabeled myo-inositol flux rev ealed that one positive charge is translocated with each molecule of m yo-inositol, consistent with cotransport of one proton, The transport concentration dependence on both species suggested ordered binding of a proton followed by a molecule of myo-inositol, In the absence of myo -inositol, a voltage-dependent capacitance was observed that correlate d with the transporter expression level, This charge movement obeyed a Boltzmann function, which was used to estimate a turnover of 0.70 +/- 0.06 s(-1) at -60 mV. The pH and voltage dependence of the charge mov ements were simulated with a model involving alternating access of int ernal and external protons to sites within an occluded pore.