The role of horse hemoglobin and horse heart myoglobin as green catalysts in the bioremediation of four classes of industrial textile dyes

Abstract

Commercial textile dyes are a leading cause of industrial water pollution. We report here the results of the first study to assess the bioremediation potential of the heme proteins horse hemoglobin and horse heart myoglobin in the rapid decolorization of four common classes of synthetic dyes with hydrogen peroxide. The results demonstrate that horse hemoglobin or horse heart myoglobin, along with hydrogen peroxide, decolorize all four tested dyes, namely, the anthraquinone dye, RB-19; the azo dye, xylidine ponceau; the indigoid dye, indigo carmine; and the triarylmethane dye, malachite green. Michaelis-Menten kinetics indicate that horse hemoglobin decolorized all four dye types significantly faster and more efficiently than horse heart myoglobin, under a wide range of pH conditions (6.5 to 9.0) and hydrogen peroxide concentrations (5 to 60 mM), suggesting that the difference arises in part from the presence of four heme sites in tetrameric horse hemoglobin that are involved in the decolorization reaction, as compared to the single heme site in monomeric horse heart myoglobin. Horse hemoglobin and horse heart myoglobin both decolorized indigo carmine and the anthraquinone dye RB-19 significantly faster than the azo dye xylidine ponceau and the cationic triarylmethane dye malachite green, suggesting that the structures of the dyes and specific interactions between the dye and the heme protein also affect the observed decolorization rates. This study demonstrates the promise of these two heme proteins as potential green catalysts for decolorizing a wide range of industrial dyes and organic compounds in water treatment.