ORIGINAL PAPER The Effects of Copper (II) Ions on Enterococcus hirae Cell Growth and the Proton-Translocating F o F 1 ATPase Activity Zaruhi Vardanyan • Armen Trchounian Published online: 30 March 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Enterococcus hirae grow well under anaerobic conditions at alkaline pH (pH 8.0) producing acids by glucose fermentation. Bacterial growth was shown to be accompanied by decrease of redox potential from positive values (*?35 mV) to negative ones (*-220 mV). An oxidizer copper (II) ions (Cu 2? ) affected bacterial growth in a concentration-dependent manner (within the range of 0.05 mM to 1 mM) increasing lag phase duration and decreasing specific growth rate. These effects were observed with the wild-type strain ATCC9790 and the atpD mutant strain MS116 (with absent b subunit of F 1 of the F o F 1 ATPase) both. Also ATPase activity and proton– potassium ions exchange were assessed with and without N,N 0 -dicyclohexylcarbodiimide (DCCD), inhibitor of the F o F 1 ATPase. In both cases (DCCD ±), even low Cu 2? concentrations had noticeable effect on ATPase activity, but with less visible concentration-dependent manner. Changes in the number of accessible SH-groups were observed with E. hirae ATCC9790 and MS116 membrane vesicles. In both strains Cu 2? markedly decreased the number of SH-groups in the presence of K ? ions. The addition of ATP increased the amount of accessible SH- groups in ATCC9790 and decreased this number in MS116; Cu 2? blocked ATP-installed increase in SH- groups number in ATCC9790. H ? –K ? -exchange of bac- teria was markedly inhibited by Cu 2? , but stronger effects were detected together with DCCD. Moreover, discrimi- nation between Cu 2? and other bivalent cation—Ni 2? was shown. It is suggested that Cu 2? ions inhibit E. hirae cell growth by direct affect on the F o F 1 ATPase leading to conformational changes in this protein complex and decrease in its activity. Keywords Cu 2? Á Bacterial growth Á Proton transport Á F o F 1 ATPase Á SH-groups Á Enterococcus hirae Introduction Enterococcus hirae grow well under anaerobic conditions which is accompanied by acidification of the medium and changes in environment redox potential (E h ). It is known that positive values of E h inhibit the anaerobic bacteria growth (for reviews, see [10, 38]) while E h negative values are required for bacterial growth [4, 7, 22]. The latter can be inhibited by oxidizers, which maintain E h on positive level [4, 15], and stimulated by reducers, which decrease E h to negative values [14]. Moreover, E h affects proton-motive force by changing pH gradient across the membrane [31]. Low concentrations of oxidizing Cu 2? ions are required for Escherichia coli and the other bacteria (for reviews, see [11, 29, 32]) whereas in considerably higher concentrations they can cause a number of toxic cellular effects inhibiting E. coli cell growth [15, 39], which can be explained by alteration of H ? flux through the F o F 1 ATPase as installed by Kirakosyan and Trchounian [15] and inhibition of hydrogenase activity associated with the F o F 1 ATPase as determined by Kirakosyan et al. [16], by increase in surface charge density as shown by Volodina et al. [39] as well as by changes in membrane permeability as suggested for this bacterium by Lebedev et al. [18]. The change in H ? -per- meability and the other properties of bacterial membrane may be related to membrane proteins re-organization or changed functional activity, and that might depend on proteins thiol groups’ state and distribution. In accordance Z. Vardanyan Á A. Trchounian (&) Department of Biophysics of the Biological Faculty, Yerevan State University, 1 A. Manoukian Str, 0025 Yerevan, Armenia e-mail: Trchounian@ysu.am Cell Biochem Biophys (2010) 57:19–26 DOI 10.1007/s12013-010-9078-z