The biological activity of hydrogen peroxide V. The crystal structure of a histidine-peroxide adduct and its biological activities

Abstract

Crystals were prepared from a mixture of l-histidine ( l-His) and hydrogen peroxide (H 2O 2) and tested for biological activity in human embryonic fibroblasts. The crystal structure was determined by X-ray diffraction to be that of an adduct, in which the H 2O 2 molecule forms a OHN hydrogen bond with N δ of the side chain of l-His. A 10-min treatment with this adduct in solution (25–150 μM) induced more marked chromosomal aberrations and more single-strand breaks (SSB) in DNA than H 2O 2 itself, and these effects were generated in a dose-dependent manner. With respect to the induction of dicentric and ring chromosomes (Dic and Ring), a maximum frequency of 1.3 per cell was obtained at 75 μM. This maximum level of induction by the adduct was 6–7 times higher than that by H 2O 2 and was comparable to that by the mixture of l-His and H 2O 2 which we observed in our previous studies. The most effective dose for such induction by the adduct was also similar to that of l-His in the mixture. Cell growth was inhibited more strongly by the adduct than by H 2O 2 alone after a 60-min treatment at 75 μM, although there was not much difference between their effects after a 10-min treatment at 75 μM. The reactive factors derived from the adduct were the same as those in the mixture, and are suggested to be derivatives of H 2O 2, hydroxyl radicals (·OH) and/or singlet oxygen ( 1O 2). Thus, the patterns of induction and kinetics of the biological activities of the adduct were very similar to those of the mixture, but not to those of H 2O 2. These results suggest that the formation of the adduct plays an important role in the enhancement of the expression of the biological activity of H 2O 2 by the coadministration of l-His and H 2O 2, which we observed in our previous study.