Na-H Exchangers and Intracellular pH Regulation

Re^2: symposium 254

Dr, Kinsella: that's great. At least the things are consistent. As you know of course, no method, especially target size analysis is perfect. There is a lot of literature of the Na-pump showing that the target size of the pump depends on what you are measuring.

On Tue Dec 8, James Kinsella wrote
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>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.
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Tue Dec 8