RAPISARDA Viviana Andrea
congresos y reuniones científicas
Specific extracellular reduction of cupric ions in Escherichia coli depends exclusibily on certain respiratory chain components
RAPISARDA, V. A.; VOLENTINI, S. I.; MASSA, E. M.; FARÍAS, R. N.; RODRÍGUEZ-MONTELONGO, L.
Iguazu, Misiones (Argentina)
Congreso; XL Annual Meeting Argentine Society for Biochemistry and Molecular Biology; 2004
The aerobic respiratory chain (RC) of Escherichia coli (E. coli) is located in the inner membrane. We previously identified in the RC two sites of electron transfer to membrane-bound copper leading to reduction of Cu(II) to Cu(I): Site I, depending on NADH dehydrogenase-2 (NDH-2) and Site II, depending on quinones. We demonstrated also that purified NDH-2 has cupric-reductase activity. To elucidate the possible role in the extracellular Cu(II)-reduction of the members of these two Sites of the RC, we performed in vivo studies using E. coli strains that either contain or are deficient in the different components. Cells harvested in exponential phase of growth were exposed for 1 hour to 20 mM citrate-200 uM CuSO4 in the presence or in the absence of bathocuproine disulfonate. This chelator specifically binds Cu(I) and develops a colored complex. Our results demonstrated that the mutant in both NDH-2 and quinones did not generate extracellular Cu(I), while the negative mutants for quinones or NDH-2 reduce about 50 % less Cu(II) than the wild-type strain. These results strongly evidence that NDH-2 and quinones are the main players involved in the cellular cupric-reduction, a relevant biological process related to the import/export system and the homeostasis of copper.