Reactions of the wurster's red radical cation with hemoglobin and glutathione during the cooxidation of N, N-dimethyl- p-phenlenediamine and oxyhemoglobin in human red cells

Abstract

Listen

Translate article

N, N-Dimethyl- p-phenylenediamine (DMPD) reacted directly with oxyhemoglobin under formation of ferrihemoglobin and, presumably, the N, N-dimethyl- p-phenylenediamine radical cation (DMPP •+). The apparent second-order rate constant of this reaction was 1 M −1 s −1 (pH 7.4, 37°C). The reaction rate was diminished by catalase (by 1 3 ) and by superoxide dismutase (by 1 5 ). The apparent second-order rate constant of ferrihemoglobin formation by DMPD •+ was 5 × 10 3 M −1 s −1. Since DMPD •+ is disproportionated by 50% at pH 7.4, the quinonediimine could not be excluded as the ultimate ferrihemoglobin forming oxidant. To prove this hypothesis, the disproportionation equilibrium was shifted to the radical side by addition of excess DMPD. Ferrihemoglobin formation was thereby increased, indication that the radical was the responsible oxidant. In contrast to ferrihemoglobin formation, reactions with glutathione occurred predominantly with the quinonediimine. The second-order rate constant of this reaction was 4 × 10 5 M −1 s −1 which approaches the value obtained with p-benzoquinone. In contrast to the corresponding reactions of the N, N, N′, N′-tetramethyl- p-phenylenediamine radical cation, the disproportionation reaction of DMPD •+ was very fast, k = 2 × 10 6 M −1 s −1. Formation of glutathione disulfide was negligible and the main reaction products were two isomeric glutathione adducts, 2- and 3-(glutathione- S-yl)- N, N-dimethyl- p-phenylenediamine. In human erythrocytes, DMPD produced many equivalents of ferrihemoglobin, diminished glutathione and produced both thioethers. In contrast to ferrihemoglobin formation, DMPD and glutathione disappearance as well as thioether appearance occured only after a marked lag phase. The calculated steady state concentration of DMPD •+ was only 4 × 10 −6 the DMPD concentration, as long as ferrihemoglobin was low. At increasing ferrihemoglobin higher steady state concentrations of the radical are attained. In fact, preformed ferrihemoglobin in red cells significantly accelerated DMPD and glutathione disappearance. This effect was completely prevented in the presence of ferrihemoglobin-complexing cyanide. The presented experiments once more appoint blood as a metabolically competent organ for the biotransformation of aromatic amines.