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Write a 12 pages paper on oxidation of methionine by singlet oxygen. Its electron arrangement is different from abundant normal diradical triplet oxygen. Singlet oxygen can be formed from triplet oxygen with the assist of photosensitizers, like Rose Bengal. Such compounds use light to convert triplet into singlet oxygen. Due to low activation energy and its electron configuration singlet oxygen is a highly reactive molecule and can readily form bonds with a number of organic molecules. It is less stable than the normal form of oxygen. However, depending on the environment singlet oxygen has the possibility to exist for more than one hour at room temperature. (Schweitzer, et al., 2003) One of the reactions that singlet oxygen can take part in, is the oxidation of amino acid residues of proteins. Cysteine and methionine residues are particularly susceptible to such forms of oxidation. In contrast to oxidation of other amino acids, this type of oxidation is reversible. Both R- and S-stereoisomers of methionine sulfoxide form as a consequence of methionine residue oxidation. The reaction can be reversed with the aid of stereospecific methionine sulfoxide reductases which can be found in most cells. The enzyme catalyses the formation of methionine residues from methionine sulfoxide (Carey, et al., 1984).