EFFLUX MECHANISMS OF RESISTANCE TO CADMIUM, ARSENIC AND ANTIMONY IN PROKARYOTES AND EUKARYOTES

Resistance to toxic metals is ubiquitously found in prokaryotes, both gram positive and gram negative, and in all types of eukaryotes, inclu ding fungi, plants, protozoans, and animals. In both prokaryotes and e ukaryotes, toxic metals are extruded from cells through afflux transpo rt systems to confer this resistance. Although the chemical substrates recognized by each transport system vary considerably, many heavy met al and metalloid translocating ATPases have been identified by evoluti onarily unrelated pumps that have evolved the same function. Among the se efflux mechanisms of resistance to heavy metals and metalloids, bac terial cadmium resistance is mediated by a primary transporter while t he thiol-linked efflux systems have developed for cadmium resistance i n eukaryotes. In contrast, bacterial resistance to arsenicals and anti monials 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 aspect s of the efflux mechanisms related to cadmium, arsenic, and antimony r esistance in prokaryotes and eukaryotes are discussed in detail in the present review.