Reaction of Azide Radicals with Amino Acids and Proteins

Abstract

SummaryThe azide radical N·3 reacts selectively with amino acids, in neutral solution preferentially with tryptophan (k(N·3 + TrpH) = 4·1 × 109 dm3 mol−1s−1) and in alkaline solution also with cysteine and tyrosine (k(N·3 + CyS−) = 2·7 × 109 dm3 mol−1s−1 and k(N·3 + TyrO−) = 3·6 × 109 dm3 mol−1s−1). Oxidation of the enzyme yADH by N·3 involves primary attacks, mainly at tryptophan residues, and subsequent slow secondary reactions. N·3-induced inactivation of yADH is likely to occur upon oxidation of tryptophan residues in the substrate binding pocket (58-TrpH and 93-TrpH) since the substrate ethanol, although unreactive with N·3, protects yADH and since elADH, which does not contain tryptophan in the substrate pocket, is comparatively resistant against N·3-attack. N·3 exhibits low reactivity with nucleic acid derivatives and it is inert towards aliphatic compounds such as methanol and sodium dodecylsulphate.