Electrochemistry of vitamin B12. I. Role of the base-on/base-off reaction in the oxidoreduction mechanism of the B12r-B12s system

Lexa, Doris; Savéant, Jean‐Michel

doi:10.1021/ja00425a039

Cited by 119 publications

(84 citation statements)

References 5 publications

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“…First, cob(I)alamin is very reactive, and, if left unprotected, it is rapidly oxidized to Co 2+ . Second, the midpoint redox potential of the Co 2+ /Co 1+ couple [E°′ = -610 mV, (Lexa & Saveant 1976)] is too low for any known cellular reductant, thus the generation of cob(I)alamin is a challenging, thermodynamically unfavorable reaction. ACA enzymes solve both problems by preferentially binding Co 2+ corrinoids, and generating a four-coordinate species that can be reduced by free or protein bound dihydroflavins (Mera & Escalante-Semerena 2010) (Fig.…”

Section: Formation Of the Co-c Bond; The Corrinoid Adenosylation Pathwaymentioning

confidence: 99%

Multiple roles of ATP:cob(I)alamin adenosyltransferases in the conversion of B12 to coenzyme B12

Mera

Escalante‐Semerena

2010

Appl Microbiol Biotechnol

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Our mechanistic understanding of the conversion of vitamin B12 into coenzyme B12 (a.k.a. adenosylcobalamin, AdoCbl) has been substantially advanced in recent years. Insights into the multiple roles played by ATP:Cob(I)alamin adenosyltransferase (ACA) enzymes have emerged through the crystallographic, spectroscopic, biochemical, and mutational analyses of wild-type and variant proteins. ACA enzymes circumvent the thermodynamic barrier posed by the very low redox potential associated with the reduction of cob(II)alamin to cob(I)alamin by generating a unique four-coordinate cob(II)alamin intermediate that is readily converted to cob(I)alamin by physiological reductants. ACA enzymes not only synthesize AdoCbl, they deliver it to the enzymes that use it, and, in some cases, enzymes whose function is needed to maintain the fidelity of the AdoCbl delivery process have been identified. Advances in our understanding of ACA enzyme function have provided valuable insights into the role of specific residues, and into why substitutions of these residues have profound negative effects on human health. From an applied science standpoint, a better understanding of the adenosylation reaction may lead to more efficient ways of synthesizing AdoCbl.

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Section: Formation Of the Co-c Bond; The Corrinoid Adenosylation Pathwaymentioning

confidence: 99%

Multiple roles of ATP:cob(I)alamin adenosyltransferases in the conversion of B12 to coenzyme B12

Mera

Escalante‐Semerena

2010

Appl Microbiol Biotechnol

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“…37 By examining pH effects and electron-transfer kinetics, the potentials and K a values for all observed protonated and base-on/base-off species were de-• termined. A mechanism for this couple was pro-< posed which involved the B 1 2 r / B , 2 s redox pair 1 and species arising from deprotonation of the r coordinated water and benzimidazole ring, as well > as the base-on/base-off equilibrium (Scheme 4).…”

Section: Vitamin Bi 2 and Related Cobalaminsmentioning

confidence: 99%

Bioelectrochemistry: An Examination of Some Examples

McCreery¹,

Wilson²

1978

C R C Critical Reviews in Analytical Chemistry

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“…109 Solvent, electron flux (current density), and pH affect the rate of the oxidationreduction processes of vitamin B12. [112][113][114] At pH 2.8 and higher, the 5,6-dimethylbenzimidazole branch of the cobalamin decouples from an axial positions of the cobalt nucleus. 113 The electrochemistry of vitamin B12 derivatives are unique among the water soluble vitamins (E i E).…”

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confidence: 99%

Critical Review—Electrochemical Properties of 13 Vitamins: A Critical Review and Assessment

Lovander

Lyon

Parr

et al. 2018

J. Electrochem. Soc.

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Review of the literature on the currently recognized, thirteen vitamins yields an overview of the electrochemical properties that include estimates of the formal potentials at physiological pH and identification of the general classes of redox mechanisms. All vitamins are electroactive and map a range of formal potentials E 0 over a 3 V window. The vitamins are grouped as lipid soluble (vitamins A, D, E, and K) and water soluble (B vitamins and vitamin C). Mechanisms are grouped as single electron transfer agents (B3, B7, B2, C, and D), vitamins that can be both oxidized and reduced (B1, B5, B6, B9, and E), and vitamins that undergo two successive, distinct reductions (B12 and K). Vitamin A voltammetry is uniquely complex. Plot of the formal potentials on a potential axis allows assessment of mechanistic paths to vitamin recycling, antioxidant behavior, pH dependence, electrochemical stability in air, acid, and water, electrochemical instability of vitamin pairs, and cooperative interactions between vitamins in medicine. The potential axis is shown as an effective tool for mapping thermodynamically complex interactions. By modern standards, the US federal government identifies 13 vitamins.3 The water soluble vitamins are vitamin C and the eight B vitamins (B1, B2, B3, B5, B6, B7, B9, B12). The lipid or fat soluble vitamins are A, D, E, and K. The fat soluble vitamins can accumulate in the body whereas the water soluble vitamins do not. There are no current vitamins designated beyond E except for K because materials historically assigned the interposed letter designations either no longer fall under the modern definition of vitamin or several related materials were reclassified. Several vitamins exist in different but related chemical structures.Questions considered in this perspective include whether all vitamins are electroactive; what is the redox potential of the vitamins; what are the kinetics and mechanisms of vitamins on oxidation and reduction; when are vitamins antioxidants; are vitamins stable to water and oxygen; do vitamins interact cooperatively. Although papers are available on the electrochemistry and voltammetry of individual vitamins, no single resource summarizes the electrochemical data for all vitamins. This review compiles and critically assesses the available literature on vitamin voltammetry. The compiled data serve to develop perspective on the electrochemical properties of vitamins and the role of vitamins individually and collectively as electroactive species. This CRES 3 T review assimilates fundamentals of thermodynamics and estimated formal potentials, kinetics, and mechanisms as assessed voltammetrically for individual vitamins to provide perspective on the collective electrochemical properties of the thirteen vitamins. Perspective on vitamin electrochemical properties may contribute to assess yet more complex bioelectrochemical processes. * Electrochemical Society Student Member.* * Electrochemical Society Fellow. z E-mail: johna-leddy@uiowa.eduThe review contains two main sections....

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Electrochemistry of vitamin B12. I. Role of the base-on/base-off reaction in the oxidoreduction mechanism of the B12r-B12s system

Cited by 119 publications

References 5 publications

Multiple roles of ATP:cob(I)alamin adenosyltransferases in the conversion of B12 to coenzyme B12

Multiple roles of ATP:cob(I)alamin adenosyltransferases in the conversion of B12 to coenzyme B12

Bioelectrochemistry: An Examination of Some Examples

Critical Review—Electrochemical Properties of 13 Vitamins: A Critical Review and Assessment

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