Hemoglobin peroxidase reaction of hemoglobin efficiently catalyzes oxidation of benzo[a]pyrene.

Its high molecular weight endows benzo[a]pyrene (BaP) with strong adsorption to soil, causing serious soil contamination. Our previous study has reported that hemoglobin (Hb) is able to oxidize organic pollutants in the presence of H2O2. This present study showed that Hb catalytic mechanism for BaP oxidation was similar to that of lignin peroxidase. 2-Methyl-3-vinylmaleimide was confirmed as a major degradation intermediate of BaP by Hb catalysis. In addition, BaP was shown to be degraded by heme (Hm)-catalyzed reaction, suggesting that Hm of Hb is the essential catalytic center. Rate constants (k) for BaP oxidation by Hm-catalyzed reaction were 0.4954 h-1. The major degradation intermediate by Hm-catalyzed reaction is 3,3',5,5'-tetramethylbiphenyl. While values of Km and Vmax of Hb and Hm are very similar, kcat values was 100 times higher with Hb than with Hm. But kcat value for Hb was much lower than that for lignin peroxidase H2. All the results above suggested that Hb-catalyzed reactions efficiently degrade BaP in aqueous condition. Thus, we suggest that Hb for oxygen carrier in blood could be employed as a biocatalyst (i.e., hemoglobin peroxidase) for BaP degradation in the environment, due to the high availability of Hb.

Optimization of hydrogen peroxide-to-hemoglobin ratio for biocatalytic mineralization of polycyclic aromatic hydrocarbons (PAHs)-contaminated soils.

This study investigates the efficiency of hemoglobin (Hb)-catalyzed biocatalytic reactions for removal of polycyclic aromatic hydrocarbons (PAHs) in a historically PAHs-contaminated soil and of benzo(a)pyrene (BaP) in an artificially BaP-contaminated soil. PAHs removal tests at various H2O2-to-Hb mass ratios (0-3.7) showed that the PAHs removal was greater at H2O2-to-Hb mass ratio of ≥3. This was attributed to the greater removal of high molecular weight PAHs at higher H2O2-to-Hb mass ratios. The BaP removal increased from 36% to 85% with increasing H2O2-to-Hb mass ratio from 1 to 3, and further increase in H2O2-to-Hb mass ratio decreased the BaP removal. Thus, the optimal H2O2-to-Hb mass ratio for BaP removal was determined to be 3 in the artificially BaP-contaminated soil. The BaP removal in the presence of only Hb can be attributed to the capture of BaP by Hb. The increased BaP removal in the presence of H2O2 is likely due to BaP mineralization as the BaP removal and the CO2 generated showed a strong positive correlation (R2 = 0.999). Overall, this study shows that the Hb-catalyzed biocatalytic reactions can effectively remove PAHs in soil.