FIG. 3.

Oxidation and reduction of Met. Oxidation of Met will yield Met-SO in either R or S diastereomeric forms. On free Met, this will occur randomly; however in the context of a protein or under influence of an enzyme, preference for one or the other could occur. Reduction of the R form can only be catalyzed by MSRA, whereas the S isoform can only be reduced by MSRB. These two enzymes are differentially expressed. It has been proposed that diastereomer-specific oxidation and resolution of protein-Met-SO forms might participate in redox regulation (see text). Met-SO, Met-sulfoxide; MSR, Met-SO reductase.