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Enzyme reduces cysteine sulfinic acid residues
A newly identified enzyme can convert highly oxidized cysteine amino acid residues back to cysteine, according to biochemist Michel B. Toledano and coworkers at the French Atomic Energy Commission (CEA), in Gif-sur-Yvette. In some proteins, peroxide can oxidize cysteine's thiol side chain to sulfinic acid (–SO2H). This modification was long considered to be irreversible. Recently, however, Sue Goo Rhee and coworkers at NIH showed that human cells contain an unidentified enzyme capable of doing the job (C&EN, May 26, page 36). Now, Toledano's team has identified an enzyme present in yeast and humans that fits the bill [Nature, 425, 980 (2003)]. They propose that the sulfiredoxin enzyme first converts sulfinic acid to a sulfinic phosphoryl ester (–SO2PO32–). A cysteine thiol in sulfiredoxin then attacks the sulfur atom, yielding an intermolecular thiosulfate that can be reduced to cysteine by biological thiols, they suggest. "Sulfiredoxin is likely to be involved in the repair of proteins containing cysteine sulfinic acid modifications and in signaling pathways involving protein oxidation," the authors write.
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