DCCD-Sensitive, Na+-Dependent H+-Influx Process Coupled to Membrane Potential Formation in Membrane Vesicles of Halobacterium halobium

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Abstract
The effects of N,N'-dicyclohexylcarbodiimide (DCCD) on light-induced H+-trans-port and transmembrane electric potential (ΔΦ) formation were studied in the membrane vesicles of Halobacterium halobium R1M1. In accordance with our previous finding of the existence of two DCCD-binding components in vesicle membrane using 14C-DCCD (Konishi & Murakami FEDS Lett. 169, 283–286 (1984)), DCCD inhibited the H+-influx process biphasically; that is, the H+-influx process which is electrically silent was initially inhibited at concentrations below 30 nmol of DCCD/mg vesicle protein, while another H+-influx process which is coupled to ΔΦ formation was secondarily inhibited above this concentration of DCCD. The latter H+-influx process was highly dependent on the Na+ concentration. The extents of Na+-dependent recovery of ΔΦ formation and H+-influx were quantitatively correlated. From these results, it was concluded that the second DCCD-sensitive H+-influx process which is coupled to ΔΦ formation is due to the hypothetical Na+/H+-antiporter postulated by Lanyi and MacDonald (Biochemistry 15, 4608–4614 (1976)). It was also found that Li+ can be substituted for Na+ in this system, as is the case with Na+/H+-antiporters found in other organisms.