Oxidation of the methionine residues of Escherichia coli ribosomal protein L12 decreases the protein's biological activity.

Oxidation of ribosomal protein L12 with hydrogen peroxide converts the three methionine residues to methionine sulfoxide. The oxidized protein has a decreased ability to bind to ribosomes, interact with ribosomal protein L10, be precipitated by L12 antiserum, and serve as substrate for the acetylating enzyme that converts L12 to L7. Full activity of L12 is regained when the protein is reduced with 2-mercaptoethanol. Sedimentation equilibrium analysis shows that oxidation of the methionine residues in L12 causes the conversion of the protein from the dimer to the monomer form, and the results indicate that the dimer is the active form of the protein in the above reactions.