title: The electrochemistry of 5-hydroxybenzimidazolylcobamide.
abstract: Methanogenic archaea typically contain 5-hydroxybenzimidazolylcobamide (cba-HBI) as the prosthetic group of a number of methyltransferases involved in their central metabolic pathways. In this paper the (acidic) dissociation constants and standard oxidation-reduction potentials of the Co3+/Co2+ and Co2+/Co1+ couples of isolated aquo-cba-HBI were measured. Comparison of the data to those established for 5,6-dimethylbenzimidazolylcobamide (cobalamin) showed that the 5-hydroxybenzimidazolyl (HBI) nucleotidic base hardly affected the redox potentials. HBI, however, proved to be the weaker ligand, thus favoring "base-off" formation. The implications for the functioning of cba-HBI in biochemical methyl group transfer reactions are discussed.
authors.affiliation: Department of Microbiology, Faculty of Science, University of Nijmegen, The Netherlands.
authors.forename: P J
authors.initials: PJ
authors.lastname: Daas
authors.forename: J T
authors.initials: JT
authors.lastname: Keltjens
authors.forename: W R
authors.initials: WR
authors.lastname: Hagen
authors.forename: C
authors.initials: C
authors.lastname: van der Drift
mesh_terms: D004563:Electrochemistry; D008024:Ligands; D017021:Methanosarcina barkeri / Q000737:chemistry; D015394:Molecular Structure; D010084:Oxidation-Reduction; D014805:Vitamin B 12 / Q000031:analogs & derivatives* / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D008024:Ligands; D014867:Water; C051329:factor III, vitamin B 12; D014805:Vitamin B 12