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

Crystals were prepared from a mixture of L-histidine (L-His) and hydrogen peroxide (H2O2) 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 H2O2 molecule forms a OH-N hydrogen bond with N delta of the side chain of L-His. A 10-min treatment with this adduct in solution (25-150 microM) induced more marked chromosomal aberrations and more single-strand breaks (SSB) in DNA than H2O2 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 microM. This maximum level of induction by the adduct was 6-7 times higher than that by H2O2 and was comparable to that by the mixture of L-His and H2O2 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 H2O2 alone after a 60-min treatment at 75 microM, although there was not much difference between their effects after a 10-min treatment at 75 microM. The reactive factors derived from the adduct were the same as those in the mixture, and are suggested to be derivatives of H2O2, hydroxyl radicals (.OH) and/or singlet oxygen (1O2). 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 H2O2. These results suggest that the formation of the adduct plays an important role in the enhancement of the expression of the biological activity of H2O2 by the coadministration of L-His and H2O2, which we observed in our previous study.