Electron Transfer From Azide Radical To Histidine Generates Histidinyl Radical

The formation of histidinyl radical (HR), which is a product of electron transfer reaction between histidine and some free radicals, was studied by pulse radiolysis. The reaction between histidine and azide radicals was found to produce HR, which has a distinct absorption spectrum with peaks at 300, 480 and 520 nm. The formation of HR was found to depend solely on the concentration of azide radicals, with the first order rate of 1.46 x 10⁴ s^-1. The implication of the formation of HR in an enzyme, which has histidine as the crucial amino acid to its activity, is discussed.