The Antibacterial Effect And Mechanism Of Soybean Peroxidase-Hydrogen Peroxide-Potassium Iodide System

A system, made up of peroxidease.hydrogen peroxide and halide, was studied widely for its bactericidal and bacteriostatic action. Nowadays, most of the studies are focus on mammalian peroxidase(Lactoperoxidase,myeloperoxidase). Mammalian peroxidase is hard to be obtained and very expensive. So a new peroxidase which have the similar structure and catalytic activity was expected to take the place of mammalian peroxidase. The peroxidase would have potential significance in academic research and application.Soybean peroxidase(SBP) obtained from the soybean coats belongs to class III of peroxidase syperfamily(EC1.11.1.7) with hemachrome as its prosthetic group. It is similar to other peroxidase in structure and function. Its raw material was rather cheap and easily obtained. SBP was highly reactive towards both organic and inorganic substrates.SBP was also very stable at high temperature, wide pH and so on. Due to these advantages,more and more attentions are paid to the studies of SBP.Our studies showed that soybean peroxidase-hydrogen peroxide-potassium iodide system was effective on bactericidal and bacteriostatic action. The system's antimicrobial action can be influenced by organic materials and pH etc. Killing kinetics of the system for E.coli and S.aureu indicated its rapid antimicrobial action. The stability of the system was also very high, as it was still active after being placed for 4 hours at 37℃.The antibacterial mechanism of SBP-H₂O₂-KI system was studied. The results of ESR experiments demonstrated that there was no free radical formation in SBP-H₂O₂-KI system. In the same H₂O₂ concentration, however, free radical was detected in the ferrous ion-hydrogen peroxide system (a typical system generating hydroxy radical). Campared to the Fe²⁺-H₂O₂ system, SBP-H₂O₂-KI system had absolute lethal effect on E.coli3\343 and S.aureu. The antibacterial effect of SBP-H₂O₂-KI system was not due to the production of the free radical which generally reported. We speculated that iodide ion performed a mediated role in SBP-H₂O₂-KI system. The antibacterial effect of SBP-H₂O₂-KI system was due to the activating oxidation state of iodine. We detected obvious absorption peak of free radical in the Fe²⁺-H₂O₂ -KI system which had efficiency on antibacterial action. However, when making a comparison between the catalytic activity of Fe²⁺ and SBP, we found that the antibacterial action of Fe²⁺-H₂O₂ -K.I system was lower than SBP-H₂O₂-KI system. It explained that the catalytic activity of SBP in the H₂O₂-KI system was higher than Fe²⁺, so the SBP in H₂O₂-KI system cannot be substituted by Fe²⁺ in the aspect of catalytic activity. We speculated the lethal effect of activating oxidation state of iodine was more effective than free radical.We also made further experiment to study the variety of sensitivity of cells for the SBP-H₂O₂-KI system in the sublethal level. The sensitivity of E.coli3\343 did not vary from the first generation to the fifteenth generation, but reduced a little from the beginning of the sixteenth generation. The sensitivity of S.aureu brought down from the beginning of the first generation, but fluctuated in a certain range and kept steadily from the second generation to the fifteenth generation. The variety of sensitivity of cells in sublethal level may be caused by physiological adaptation or heritable mutation, and the detailed reason can be confirmed in the further study.