Thermodynamics of Iodine Solubility and Triiodide Ion Formation in Water and in Deuterium Oxide

Ramette, Richard W.; Sandford, R. W.

doi:10.1021/ja00950a005

Cited by 134 publications

(80 citation statements)

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“…Unraveling this "cramming" method could provide a blueprint for the biomimetic design of artificial enzymes with extended functions. (35). Other chemicals obtained from Wako and Aldrich were used without further purification.…”

Section: Discussionmentioning

confidence: 99%

Unique coupling of mono- and dioxygenase chemistries in a single active site promotes heme degradation

Matsui

Nambu

Goulding

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

101

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Bacterial pathogens must acquire host iron for survival and colonization. Because free iron is restricted in the host, numerous pathogens have evolved to overcome this limitation by using a family of monooxygenases that mediate the oxidative cleavage of heme into biliverdin, carbon monoxide, and iron. However, the etiological agent of tuberculosis, Mycobacterium tuberculosis, accomplishes this task without generating carbon monoxide, which potentially induces its latent state. Here we show that this unusual heme degradation reaction proceeds through sequential mono- and dioxygenation events within the single active center of MhuD, a mechanism unparalleled in enzyme catalysis. A key intermediate of the MhuD reaction is found to be meso-hydroxyheme, which reacts with O2 at an unusual position to completely suppress its monooxygenation but to allow ring cleavage through dioxygenation. This mechanistic change, possibly due to heavy steric deformation of hydroxyheme, rationally explains the unique heme catabolites of MhuD. Coexistence of mechanistically distinct functions is a previously unidentified strategy to expand the physiological outcome of enzymes, and may be applied to engineer unique biocatalysts.

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Section: Discussionmentioning

confidence: 99%

Unique coupling of mono- and dioxygenase chemistries in a single active site promotes heme degradation

Matsui

Nambu

Goulding

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

101

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“…-13 [17] , K2 = 2.3×10 -11 [18] K3 = 723 [19] , K4 = 22.2 [27] , K5 = 9, K6 = 0.1 [21] , and K7 = 1.3×10 13 [18] .…”

Section: Methodsmentioning

confidence: 99%

Iodine and Disinfection: Theoretical Study on Mode of Action, Efficiency, Stability, and Analytical Aspects in the Aqueous System

Gottardi

1999

Arch. Pharm. Pharm. Med. Chem.

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Although they have been in use for nearly 170 years, the mode of action of iodine‐based disinfectants is not yet clearly understood, as is manifested, for example, in diverging judgements about the relevance of the individual iodine species. Although studies based on calculated equilibrium concentrations in pure iodine solutions have already been done, there is a lack of knowledge about iodine solutions in the presence of additional iodide which would be of intrinsic importance for disinfection practice. Therefore, a re‐calculation was undertaken considering variations of this parameter in the pH range 0—14. The presented calculations concern fresh iodine solutions not affected by disproportionation (iodate formation) and provide information about the equilibrium concentrations of the species I‐, I2, I3‐, I5‐, I62, HOI, OI‐, HI2O‐, IO2‐, and H2OI+. Additional iodide and the pH value have a very pronounced influence on the individual equilibrium concentrations (several powers of ten); hence, conditions can be indicated where the number of species of virtual importance is drastically reduced. In the most common case with iodine in the presence of additional iodide at pH < 6, only I‐, I2, and I3‐ play a role. In the absence of additional iodide, at pH 8‐9 and at high dilution (c(I2) < 10‐5M), on the other hand, HOI accounts for over 90% of the oxidation capacity. At high iodide concentration (e.g. Lugol′s solution) the species I5‐ and I62‐ make up 8.2% of the oxidation capacity. The iodine cation H2OI+, frequently quoted as an active agent in disinfection, is without any relevance under the conditions occurring in practice, as are IO‐ and HI2O‐ which become important only at pH > 10. The stability problem (i.e. rate of iodate formation) arising at pH > 6 can be reduced to hypoiodous acid, as manifested in the simple rate law d[IO3‐]/dt = 0.25[HOI]3/[H+] which allows an estimation of stability under weakly alkaline conditions. The results of this study allow us to deduce general qualities of aqueous iodine solutions, such as reactivity, stability, and analytical aspects, and to estimate major disinfection‐orientated properties such as microbicidal activity, irritation, and incorporation effects. Though the calculations consider primarily preparations devoid of polymeric organic compounds capable of complexing iodine species, the results can be largely transferred to iodophoric preparations.

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“…A 2 ml aliquot was pipetted into a cuvette, and the absorbance change observed upon the addition of 50 pl of the hydroperoxide solution. Using a molar absorptivity of 2.55 x lo4 M-' cm-' (22), the hydroperoxide concentration was calculated. The solutions of hydrogen peroxide used to prepare the HRP compounds were also stored and analyzed in a similar manrer.…”

Section: Methodsmentioning

confidence: 99%

Studies on Horseradish Peroxidase. XI. On the Nature of Compounds I and II as Determined from the Kinetics of the Oxidation of Ferrocyanide

Cotton¹,

Dunford²

1973

Can. J. Chem.

269

109

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In order to investigate the nature of compounds I and I1 of horseradish peroxidase, the kinetics were studied of ferrocyanide oxidation catalyzed by these compounds which were prepared from three different oxidizing agents. The p H dependence of the apparent second-order rate constant for ferrocyanide oxidation by compound I, prepared from ethyl hydroperoxide and m-chloroperbenzoic acid, was interpreted in terms of an ionization on the enzyme with a pK, = 5.3, identical to that reported previously for hydrogen peroxide. The second-order rate constant for the compound 11-ferrocyanide reaction also showed the same p H dependence for the three oxidizing substrates. However, with more accurate results, the compound 11-ferrocyanide reaction was reinterpreted in terms of a single ionization with pK, = 8.5. The same dependence of ferrocyanide oxidation on p H suggests structurally identical active sites for compounds I and I1 prepared from the three different oxidizing substrates.Pour etudier la nature des composes I et I1 de la peroxydase de raifort, on a examine les cinetiques de l'oxydation du ferrocyanure catalysee par ces composes, qui ont ete prepares a partir de trois agents oxydants differents. L'influence du p H sur la constante de vitesse apparente du deuxieme ordre poul l'oxydation du ferrocyanure par le compose I prepare a partir de I'hydroperoxyde d'ethyle et de l'acide nz-chloroperbenzoique, a ete interpretee en fonction de I'ionisation de I'enzyme a un pK, = 5.3, identique a celle precedemrnent rapportee pour I'eau oxygenee. La constante de vitesse du second ordre pour la reaction entre le ferrocyanure et le compose 11, montre aussi la mCme relation de p H pour les trois substrats oxydants. Cependant, avec des risultats plus precis, la reaction entre le ferrocyanure et le compose I1 a ete reinterprktee par rapport a l'ionisation simple a pK, = 8.5. La mCme relation entre I'oxydation du ferrocyanure et le p H laisse penser a des sites actifs de structure identique pour les composts I et TI, prepares a partir de trois substrats oxydants differents.[Traduit par le journal]Can. J. Chern.. 51. 582 (1973) The intermediate compounds of horseradish peroxidase (HRP), that is, compound I (HRP-I) and compound PI (HRP-II), have been known for many years (1, 2). Early investigations indicated that these compounds could be formed from alkyl (3, 4) and acyl hydroperoxides (5) as well as several inorganic oxidizing agents (6). A variety of possibie structures has been proposed for these compounds (7)(8)(9)(10). Recently, it has been shown that oxygen is incorporated into compound I of ch!oroperoxidase upon its formation from m-chloroperbenzoic acid (11,12). Clearly, in addition to the electron transfer processes occurring, a portion of the peroxide must be retained at the active site upon HRP-1 formation.Although many techriiques have been applied to the study of HRP compounds (I3-17), the kinetic method, in principle, provides one of the 'Author vo whom corrsspo:.dei7ce sh~a?c% be addressed better sources of informa...

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Thermodynamics of Iodine Solubility and Triiodide Ion Formation in Water and in Deuterium Oxide

Cited by 134 publications

References 0 publications

Unique coupling of mono- and dioxygenase chemistries in a single active site promotes heme degradation

Unique coupling of mono- and dioxygenase chemistries in a single active site promotes heme degradation

Iodine and Disinfection: Theoretical Study on Mode of Action, Efficiency, Stability, and Analytical Aspects in the Aqueous System

Studies on Horseradish Peroxidase. XI. On the Nature of Compounds I and II as Determined from the Kinetics of the Oxidation of Ferrocyanide

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