Na-H Exchangers and Intracellular
pH Regulation
Re: symposium 254 James Kinsella
kinsellj@grc.nia.nih.gov
On Fri Dec 4, grover wrote
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>Dr. Kinsella:Hope you are enjoying the meeting. �Great poster. Has any one quick frozen NHE-containing vesicles and then done target size analysis using radiation inactivation to determine if the size of the transporter differs in these two states?
>Beliveau et al., 1988, BBRC 152: 484 reports on radiation inactivation of NHE. �He estimated the molecular size of active NHE to be between 3 and 4 times the size of the protomer. �Results in agreement with our hypothesis that NHE likely is a tetramer. �I would expect the target size to be the same regardless of the activity state of NHE. � �We propose that NHE is an oligomer in the membrane and that activation by internal H+'s alters the protein conformation within the oligomer. �One (or maybe more?) conformation for the "inactive" state and another conformation for the H+-dependent active state. �It is interesting that we found in Otsu et al. 1992 that 50% of the Na sites were available at alkaline pH (the "inactive" state) for a single Na turnover during the presteady-state. �The results suggest that the NHE oligomer exists under the alkaline conditions otherwise 100% of the sites would be available for the initial single turnover.
Tue Dec 8