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J. Bacteriol., May 1995, 2707-2712, Vol 177, No. 10
DH Nies
The function of the CzcABC protein complex, which mediates resistance to
Co2+, Zn2+, and Cd2+ in Alcaligenes eutrophus by cation efflux, was
investigated by using everted membrane vesicles of Escherichia coli and an
acridine orange fluorescence quenching assay. Since metal cation uptake
could not be measured with inside-out membrane vesicles prepared from A.
eutrophus and since available E. coli strains did not express the
Czc-mediated resistance to cobalt, zinc, and cadmium salts, mutants of E.
coli which exhibited a Czc-dependent increase in heavy metal resistance
were isolated. E. coli mutant strain EC351 constitutively accumulated Co2+,
Zn2+, and Cd2+. In the presence of Czc, net uptake of these heavy metal
cations was reduced to the wild-type level. Inside- out vesicles prepared
from E. coli EC351 cells displayed a Czc- dependent uptake of Co2+, Zn2+,
and Cd2+ and a cation-triggered acridine orange fluorescence increase. The
czc-encoded protein complex CzcABC was shown to be a zinc-proton
antiporter.
Copyright © 1995, American Society for Microbiology
The cobalt, zinc, and cadmium efflux system CzcABC from Alcaligenes eutrophus functions as a cation-proton antiporter in Escherichia coli
Institut fur Pflanzenphysiologie und Mikrobiologie, Freien Universitat, Berlin, Germany.
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