METALLOID RESISTANCE MECHANISMS IN PROKARYOTES

Resistance to antibiotics and other chemotherapeutic agents is becomin g a wide spread health issue, The biochemical mechanisms of resistance vary, but active efflux of the toxic agents is one of the most common , Bacterial resistances to metals provide good model systems for trans port-related resistances, One of the best understood metal resistance systems is the product of the ars operon, which provides resistance to arsenicals and antimonials, As a reflection of the ubiquity of arseni c in the environment, ars operons are found in all species of bacteria , carried in chromosomes, plasmids, and transposons, This review focus es on the biochemistry of the proteins of the ars operon of R-factor R 773, The system is novel in several respects, First, it is regulated a t the transcriptional and allosteric levels, and regulation is effecte d through cysteine thiol interaction with Bs(III) or Sb(III). Thus sof t metal-thiol chemistry provides a high affinity digital switch to tur n the regulated protein on with rapidity, The transport system that pr ovides resistance, on the other hand, uses oxyanions of arsenic or ant imony as substrates, This nonmetal chemistry allows for low affinity i nteractions of the membrane transporter with substrate, conductive wit h translocation and release of substrate on the outside of the cell me mbrane, Second, the transporter is uniquely capable of coupling to eit her electrochemical energy as a secondary carrier protein or the chemi cal energy of ATP when binding of a catalytic subunit converts it into an anion-translocating ATPase.