Inhibition of halobacterial Na+/H(+)-antiporter by carboxyl modifying reagent, EEDQ

The Inhibitory effect of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), a hydrohobic carboxyl modifying reagent, on the N,N'-dicyclohexylcarbodiimide (DCCD)-sensitive Na+/H(+)-antiporter in Archaebacterial H. halobium, was studied. The inhibition time course suggests that a single carboxyl residue is modified by EEDQ. The profile of pH dependence of EEDQ effect and the competitive binding of [14C]-DCCD and EEDQ indicate that EEDQ does not compete with DCCD for the same site but modifies one of the two functional H+ binding sites previously reported [Murakami and Konishi (1989) Arch. Biochem. Biophys. 271, 515-523].