AbstractThe gamma‐radiolysis of aqueous solutions of the peptide hormone angiotensin II‐amide and the beta‐autoradiolysis of its tritiated preparations were studied. The radiation loss and the decrease of biological activity of angiotensin II‐amide was evaluated. The main fractions of radiation products were separated and compared with the products formed during the storage of tritiated angiotensin II‐amide. The principal radiation processes taking place during the irradiation of angiotensin II‐amide were discussed.

The loss of histidine and the formation of additional by-products during the purification and storage of [14C(U)]-L-histidine preparations on chromatographic carriers was followed. The product formed mainly on chromatographic paper was identified as the condensation product of histidine with formaldehyde; on thin layer of silica gel mainly degradation products of histidine were obtained. Possibilities to decrease the formation of these undesirable by-products were discussed.

The dependence of G i ( - M) values of histidine on the concentration of irradiated 10 -4 -10 -1 ᴍ solutions, pH and the presence of O 2 , N 2 O and sec-butyl alcohol was investigated. In oxygen-free medium the maximum radiation sensitivity of histidine was found at pH 5 - 8; in oxygenated solutions it was shifted to the 6 - 11 pH range. The formation of radiation products was also studied. The course of radiation decomposition of histidine depends on the presence of oxygen and on the pH of irradiated solution.