REACTION OF TETRANITROMETHANE WITH SULFHYDRYL GROUPS IN PROTEINS

The oxidation of sulfhydryl groups with tetranitromethane has been examined using a series of model compounds. The reaction stoichiometry was determined colorimetrically by measuring the formation of nitroformate (ε350 14,400) as well as by analysis of the other reaction products. Depending on the particular thiol studied and the molar excess of tetranitromethane employed, the course of the reaction leads mainly to a disulfide or to an acidic derivative. The acidic product has been identified as a sulfinic acid by chromatographic and electrophoretic analyses and by its conversion into a sulfonic acid on oxidation with iodine. The various factors which determine the relative amounts of the two reaction products are discussed. Oxidation of protein sulfhydryl groups with tetranitromethane results primarily in disulfide formation. No indication of interprotein chain peptide-bond formation mediated by tetranitromethane could be detected. Reaction of histidine, tryptophan, and methionine peptides with tetranitromethane was observed under certain conditions demonstrating the need for caution when using this reagent to modify proteins. © 1969, American Chemical Society. All rights reserved.