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Biosynthesis of Cysteine from Serine in Bacteria and Plants

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Inorganic sulfur in the environment (primarily sulfate, but also sulfur, and sulfite) must undergo fixation to be utilized by organisms. The fixation of sulfate is largely confined to plants and bacteria and biosynthesis of cysteine represents the final step of sulfate assimilation in these organisms. Fixation begins with the formation of PAPS (3 -Phosphoadenosine-5 -Phosphosulfate). PAPS is an activated sulfate compound and an intermediate in all organisms for sulfate esterification, such as the synthesis of chondroitin sulfate. It is formed in a two-step reaction from sulfate ion and two molecules of ATP. In plants, the main pathway of sulfate reduction is via APS (Adenosine-5 -Phosphosulfate) rather than PAPS (i.e. APS can be utilized directly, without activation to PAPS, as an intermediary substrate in [...]


1.Identification of a new class of 5'-adenylylsulfate (APS) reductases from sulfate-assimilating bacteria.
Bick JA, Dennis JJ, Zylstra GJ, Nowack J, Leustek T.
J Bacteriol. 2000 Jan; 182(1):135-42.
2.Adenosine 5'-phosphosulfate (APS) kinase: diagnosing the mechanism of substrate inhibition.
MacRae IJ, Segel IH.
Arch Biochem Biophys. 1999 Jan 15; 361(2):277-82.
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