The reaction of haemoglobin and some of its derivatives with p-iodophenylhydroxylamine and p-iodonitrosobenzene

Abstract

Reactions of hemoglobin and some of its derivative with I131-labeled p-iodophenylhydroxylamine and p-iodonitrosobenzene were followed spectroscopically and also by determining the combining ratio of the radioactive substance per atom of Fe. It was shown that spectroscopic data alone are inadequate in the study of these reactions, for combination between pigment and iodo-compound may occur without accompanying change in absorption spectrum. Also, alteration in the absorption spectrum of a formed complex to that of a known blood pigment may be induced without loss of the combined radioactive material. Iodophenylhydroxylamine combines directly with hemoglobin and carboxyhemoglobin under conditions which preclude its oxidation to the nitroso compound. A series of reactions follows the addition of the iodophenylhydroxylamine to oxyhemoglobin. Three intermediates were recognized and the final product is spectroscopically similar to methemoglobin but retains one molecular equivalent of the iodo-compound. The inter-relationships of these substances were examined. Carboxyhemoglobin combines directly with iodophenylhydroxylamine or iodonitrosobenzene without loss of CO or change in absorption spectrum. When oxyhemoglobin reacts with iodonitrosobenzene, the O2 is quantitatively displaced. It is suggested that the difference in behavior between oxyhemoglobin and carboxyhemoglobin is due to the combined iodonitrosobenzene reducing the affinity of the pigment for O2; the much greater affinity of CO, however, permits the retention of the latter. It appears probable that phenylhydroxylamine and nitrosobenzene behave in a manner similiar to their iodo-derivatives, so that the complexes formed with hemoglobin and its derivatives are not necessarily dissociated in subsequent reactions, as was previously supposed.