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Methionine sulfoxide
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<p>Methionine sulfoxide is the <a href="/facts/Organic_compound/gqCNaN45">organic compound</a> with the formula CH3S(O)CH2CH2CH(NH2)CO2H. It is an <a href="/facts/Amino_acid/WDxYwBny">amino acid</a> that occurs naturally although it is formed <a href="/facts/Post-translational_modification/KMUayTIc">post-translationally</a>. </p><p><a href="/facts/Redox/Pyd5RVcj">Oxidation</a> of the <a href="/facts/Sulfur/IK0amTfM">sulfur</a> of <a href="/facts/Methionine/7neydPKo">methionine</a> results in methionine sulfoxide or methionine sulfone. The sulfur-containing amino acids methionine and <a href="/facts/Cysteine/kbqvUm6d">cysteine</a> are more easily oxidized than the other amino acids. Unlike oxidation of other amino acids, the oxidation of methionine can be reversed by enzymatic action, specifically by <a href="/facts/Enzyme/DSI1Fh7y">enzymes</a> in the methionine sulfoxide reductase family of enzymes. The three known methionine sulfoxide reductases are <a href="/facts/MSRA_(gene)/Uog8M13Q">MsrA</a>, <a href="/facts/MSRB2/5wWguNpR">MsrB</a>, and fRmsr. Oxidation of methionine results in a mixture of the two <a href="/facts/Diastereomer/ReBkFoCP">diastereomers</a> methionine-S-sulfoxide and methionine-R-sulfoxide, which are reduced by MsrA and MsrB, respectively. MsrA can reduce both free and protein-based methionine-S-sulfoxide, whereas MsrB is specific for protein-based methionine-R-sulfoxide. fRmsr, however, catalyzes the reduction of free methionine-R-sulfoxide. <a href="/facts/Thioredoxin/Up6p35ke">Thioredoxin</a> serves to recycle by reduction some of the methionine sulfoxide reductase family of enzymes, whereas others can be reduced by <a href="/facts/Metallothionein/4ntygR3A">metallothionein</a>. </p>