Publications

• Structure of a ternary complex of lactoperoxidase with iodide and hydrogen peroxide at 1.77A resolution.

  Singh P.K., Sharma P., Bhushan A., Kaur P., Sharma S., Singh T.P.

  Lactoperoxidase (LPO) is a mammalian heme peroxidase which catalyzes the conversion of thiocyanate (SCN¯) and iodide (I^-) by hydrogen peroxide (H₂O₂) into antimicrobial hypothiocyanite (OSCN¯) and hypoiodite (IO^-). The prosthetic heme group is covalently ... >> More

  Lactoperoxidase (LPO) is a mammalian heme peroxidase which catalyzes the conversion of thiocyanate (SCN¯) and iodide (I^-) by hydrogen peroxide (H₂O₂) into antimicrobial hypothiocyanite (OSCN¯) and hypoiodite (IO^-). The prosthetic heme group is covalently attached to LPO through two ester linkages involving conserved glutamate and aspartate residues. On the proximal side, His351 is coordinated to heme iron while His 109 is located in the substrate binding site on the distal heme side. We report here the first structure of the ternary complex of LPO with iodide (I^-) and H₂O₂ at 1.77 Å resolution. LPO was crystallized with ammonium iodide and the crystals were soaked in the reservoir solution containing H₂O_2. Structure determination showed the presence of an iodide ion and a H₂O₂ molecule in the substrate binding site. The iodide ion occupied the position which is stabilized by the interactions with heme moiety, His109, Arg255 and Glu258 while H₂O₂ was held between the heme iron and His109. The presence of I^- in the distal heme cavity seems to screen the positive charge of Arg255 thus suppressing the proton transfer from H₂O₂ to His109. This prevents compound I formation and allows trapping of a stable enzyme-substrate (LPO-I^--H₂O₂₎ ternary complex. This stable geometrical arrangement of H₂O₂ in the distal heme cavity of LPO is similar to that of H₂O₂ in the structure of the transient intermediate of the palm tree heme peroxidase. The biochemical studies showed that the catalytic activity of LPO decreased when the samples of LPO were preincubated with ammonium iodide. << Less

  J. Inorg. Biochem. 220:111461-111461(2021) [PubMed] [EuropePMC]

• Oxidation of Escherichia coli sulfhydryl components by the peroxidase-hydrogen peroxide-iodide antimicrobial system.

  Thomas E.L., Aune T.M.

  The chemical modification of bacterial components was studied following incubation of Escherichia coli with the peroxidase-hydrogen peroxide (H(2)O(2))-iodide (I(-)) antimicrobial system or with iodine (I(2)). The oxidation of cell sulfhydryls and the iodination of cell components were measured. B ... >> More

  The chemical modification of bacterial components was studied following incubation of Escherichia coli with the peroxidase-hydrogen peroxide (H(2)O(2))-iodide (I(-)) antimicrobial system or with iodine (I(2)). The oxidation of cell sulfhydryls and the iodination of cell components were measured. Both the peroxidase system and I(2) oxidized sulfhydryls. When the I(-) concentration in the peroxidase system was greater than 100 muM, the peroxidase system and I(2) were equivalent. That is, sulfhydryl oxidation or killing per mole of H(2)O(2) equaled that per mole of I(2). These results were consistent with peroxidase-catalyzed oxidation of I(-) to yield 1 mol of I(2) per mol of H(2)O(2). Sulfhydryls were oxidized to yield sulfenic acids and free I(-). With I(-) concentrations in the range of 10 to 100 muM, the amount of sulfhydryls oxidized by the peroxidase system could exceed the amount of I(-). Because the oxidation of sulfhydryls to sulfenic acids did not consume I(-), one I(-) ion could participate in the oxidation of many sulfhydryls. With I(-) concentrations lower than 10 muM, complete oxidation of sulfhydryls was not obtained. Incorporation of I(-) into iodinated derivatives of bacterial components partly depleted the system of I(-) and limited the formation of I(2). These results indicated that antimicrobial activity was due to peroxidase-catalyzed oxidation of I(-) to I(2), followed by I(2) oxidation of cell components. There was a direct relationship between sulfhydryl oxidation and antimicrobial action. Although iodination of bacterial components accompanied sulfhydryl oxidation, the amount of I(-) incorporation was not directly related to antimicrobial action. Also, incorporation of I(-) interfered with antimicrobial action at low I(-) concentrations. << Less

  Antimicrob. Agents Chemother. 13:1006-1010(1978) [PubMed] [EuropePMC]