Zoological Studies

Efflux  Mechanisms of Resistance to Cadmium, Arsenic and Antimony in Prokaryotes and Eukaryotes

Kan-Jen Tsai, Ching-Mei Hsu and Barry P. Rosen (1997) Resistance to toxic metals is ubiquitously found in prokaryotes, both gram positive and gram negative, and in all type of eukaryotes, including fungi, plants, protozoans, and animals. In both prokaryotes and eukaryotes, toxic metals are extruded from cells through efflux transport systems to confer this resistance. Although the chemical substrates recognized by each transport system vary considerably, many heavy metal and metalloid translocating ATPases have been identified by evolutionarily unrelated pumps that have evolved the same function. Among these efflux mechanisms of resistance to heavy metals and metalloids, bacterial cadmium resistance is mediated by a primary transporter while the thiol-linked efflux systems have developed for cadmium resistance in eukaryotes. In contrast, bacterial resistance to arsenicals and antimonials is mediated by a primary ATP-coupled pump in association with a catalytic subunit, whereas an ATP-coupled As-thiol pump has evolved to confer the resistance in eukaryotic systems. The biochemical aspects of the efflux mechanisms related to cadmium, arsenic, and antimony resistance in prokaryotes and eukaryotes are discussed in detail in the present review.