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arsenate detoxification II (glutaredoxin)

General Background While the jury is still out about whether Napoleon Bonaparte died of arsenic poisoning or cancer , it is agreed by all that arsenic is a potent toxin. Indeed, the results of exposure to high arsenic concentration in drinking water in West Bengal, India, and Bangladesh are considered by some to be the worst public health disaster in recent history . The form of arsenic influences the type and severity of toxicity. Arsenate (AsV) is a structural analog of phosphate, and inhibits phosphorylation processes. For example, ADP-arsenate spontaneously hydrolyzes, resulting in uncoupling of oxidative phosphorylation , while arsenite (AsIII) has a very high affinity for thiol groups, and thus binds to and inhibits many key enzymes that have thiol groups in their active sites. In addition, inorganic arsenic is a potent carcinogen . Arsenate enters the cell via the phosphate transport systems, such as the E. coli : PITA-MONOMER and : ABC-27-CPLX "Pst" systems. Both prokaryotes and eukaryotes reduce intracellular arsenate to arsenite. However, while prokaryotes can pump arsenite out of the cell by using a dedicated pump, multicellular organisms require other means of getting rid of the metal. Certain mammals, including humans, continue by methylating the arsenite to several methylated forms that are excreted from the organism in the urine (see : PWY-4202). About This Pathway Most microorganisms are able to detoxify arsenic species by pumping them out of the cell. This cytoplasmic detoxification system involves the arsC-encoded cytoplasmic arsenate reductase, which reduces arsenate to arsenite, and an efficient arsenite efflux pump consisting of a two-component ATPase complex. The arsA gene product is a soluble ATPase subunit, while the arsB product is an integral membrane protein. Arsenite is the preferred substrate of ArsB, as well as an activator of ArsA ATPase activity. In many cases arsB and arsC are found in an operon without an arsA gene . ArsC cytoplasmic arsenate reductases are found widely in microbes, and are found in almost all organisms with a genome larger than 2 Mb . There are three different clades of ArsC proteins in bacteria, which share no sequence similarity. The first clade includes the glutathione-glutaredoxin-coupled enzymes, and is found in many Gram-negative bacteria, as well as carried on many plasmids. The second clade consists of glutathione-only dependent enzymes, and is found only in yeast, while the third clade consists of thioredoxin-dependent enzymes, and is found in Gram-positive bacteria, as well as many Gram-negative proteobacteria. In addition, archaebacteria also possess ArsC reductases. The archaeal genes are closest to those of Gram-positive bacteria .

from BIOCYC source record: ECO_PWY-4621
Type: pathway
Taxonomic scope
:
organism-specific biosystem
Organism
:
Escherichia coli
BSID:
703167

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