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alcaligin biosynthesis

General Background Iron is an essential trace element. In the presence of oxygen, ferrous iron is oxidized to ferric iron which forms insoluble compounds, and is thus not available to organisms. As a result, the level of physiologically available iron can drop to far below 1 μM, and become growth-limiting for bacteria. To survive, many bacteria evolved specialized transport systems called siderophores, which can complex and retract ferric iron ions. The siderophores are low molecular mass compounds, and have been generally divided into three main types: catecholate-, hydroxamate-, and carboxylate-siderophores. The siderophores, which have a very high and specific affinity for |FRAME: FE+3|, are excreted out of the cell and bind the metal extracellularly. The siderophore-metal complex is transported back into the cell through specific binding proteins present in the bacterial membrane. In Gram-negative bacteria, the binding protein transports the ferric-siderophore into the periplasm, where a second transporter transports it into the cytosol |CITS: [12196166]|. About This Pathway |FRAME: CPD-11968 "Alcaligin"| is a dihydroxamate siderophore that was originally identifed in the marine bacterium |FRAME: TAX-85698 "Achromobacter xylosoxidans (then known as Alcaligenes denitrificans)"| |CITS: [Nishio88]|. Alcaligin was subsequently identified as the siderophore of the important pathogens |FRAME: TAX-520| and |FRAME: TAX-518|, previously known as bordetellin |CITS: [7860593]|. The |FRAME: G-11643| gene, which encodes the first enzyme in the pathway, was the first to be identified, by complementation of a |FRAME: TAX-518| transposon mutant defective in alcaligin biosynthesis |CITS: [8566764]|. The gene was found to be homologous to the |FRAME:TAX-562| |FRAME: G-9026| gene, which is involved in |FRAME: AEROBACTINSYN-PWY|. Two additional genes, |FRAME: G-11644| and |FRAME: G-11646|, were discovered next to |FRAME: G-11643| |CITS: [9266668]|. These genes were homologous to the aerobactin biosynthetic genes |FRAME: G-9027| and |FRAME: G-9028|, respectively. The three genes form an operon whose transcription is regulated by iron |CITS: [9266668]|. An identical operon was found in the genome of the related |FRAME: TAX-520| |CITS: [8759851]|. Subsequent work revealed three additional genes in the operon. Two tightly linked open reading frames, alcD and |FRAME: G-11645|, follow |FRAME: G-11646|, and a third gene, alcR, which encodes a transcriptional regulator, ends the operon |CITS: [9473041][9473040]|. The roles of alkD and |FRAME: G-11645| are not well understood, but a recent review proposed that alcE, which shows significant similarity to Rieske dioxygenases such as naphthalene dioxygenase, may catalyze the hydroxylation of |FRAME: CPD-11964|, yielding |FRAME: CPD-11971| |CITS: [15719346]|.

from BIOCYC source record: META_PWY-6379
Type: pathway
Taxonomic scope
conserved biosystem

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