Add time:09/08/2019         Source:sciencedirect.com

Publisher SummaryThis chapter discusses the reduction of sulfoxide and disulfides. The reducing system described for the reduction of L(—)-methionine sulfoxide consists of three separate enzymes designated I, II, and III. All three are essential for reaction that can be measured spectrophotometrically by observing the decrease in light absorption due to TPNH at 340 mμ. Each enzyme is assayed in the presence of an excess of the other two. This system is specific for TPNH, DPNH being completely inactive as a substitute. 0nly one of the four isomers of methionine sulfoxide is reduced in the system. The system is also been found to catalyze another type of reaction, the reduction of disulfide bonds that requires participation only of enzymes I and II of the three involved in reaction. The reduction of disulfides, as of L(—)-methionine sulfoxide, is specific for TPNH and does not occur with DPNH. L- or D-Cystine, and disulfide forms of mercaptoethanol, DL-lipoic acid, BAL, and glutathione are all reduced in the system at quite comparable rates. The three disulfide bonds of insulin also appear to be susceptible to this enzymatic reduction.

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