Abstract
The K + H + antiporter of a marine bacterium, Vibrio alginolyticus , is strongly dependent upon the cytoplasmic pH and functions only at an internal pH above 7.7. In alkaline buffer with an outwardly directed chemical gradient of K + (ΔpK), the internal pH was maintained at about 7.7. Addition of N-ethylmaleimide (NEM) released cellular K + and acidified the cytosol below pH 7.7. The NEM effect was reversed by the addition of 2-mercaptoethanol: K + efflux ceased, and the internal pH returned to about 7.7. In acidic buffer, the internal pH was also regulated at about 7.6 even in the absence of ΔpK. Following addition of NEM, the internal pH decreased below 7.6, dissipating ΔpH. These results suggest that NEM desensitizes the pH-dependence of the K + H + antiporter, allowing the antiporter to function at an internal pH below 7.7.
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