19] Performic acid oxidation

Abstract

Publisher Summary This chapter discusses the performic acid oxidation. The scission of disulfide bonds by oxidation with performic acid is a standard technique in protein chemistry with insulin. The virtue of the procedure is that cysteic acid and methionine sulfone, the oxidation products of cystine and methionine contains sulfur in a stable oxidation state. In addition to tryptophan and the sulfur-containing amino acids, it will oxidize phenolic groups and the hydroxyl functions of serine and threonine side chains. Conversion of cystine to cysteic acid usually proceeds in a yield of 85–90%, while oxidation of methionine to the sulfone is essentially quantitative. Since the reaction is usually conducted with a large excess of reagent, removal of this excess from the protein must be accomplished under mild conditions if over oxidation is to be minimized. Conditions suitable for the oxidation of a protein or peptide should be determined in each individual instance with the aid of amino acid analyses. Performic acid reagent, oxidation of ribonuclease, and removal of halide ion are also focused. A significant limitation to the use of performic acid oxidation for the cleavage of disulfide bonds in proteins is the concomitant destruction of tryptophan.