States of Amino Acid Residues in Proteins XIV. Glyoxal as a Reagent for Discrimination of Arginine Residues

Abstract

Several aldehydes and ketones were examined in order to explore a reagent suitable for discrimination of various states of arginine residues in proteins in terms of reactivity. The chemicals examined were glyoxal, formaldehyde, pyruvaldehydc, diacetyl and dibenzoyl, and the examinations were made with native and denatured insulin and its B chain and lysozyme [EC 3.2.1.17] as the sample proteins with arginine residues. Glyoxal was most reactive of these chemicals, and the single B22 arginine residue of the B chain and the 11 arginine residues of lysozyme reacted to the extent of approximately 80% with this reagent, while other essential amino acids were not appreciably affected by the treatment. Practically no reaction of lysinc residues, which is generally more reactive than arginine residues, is interpreted as due to an artifact; lysine residues modified with glyoxal seem to be hydrolyzed back to intact lysine on the acid treatment of glyoxal-modified protein for the assay of arginine. The B22 arginine residue in native insulin was much less reactive with glyoxal than the same residue in alkali-denatured insulin or in the B chain. This result supported strongly a previous view that the B26 tyrosine residue is hydrogen-bonded with the B22 arginine residue in the native insulin molecule.