The electrochemistry of 5-hydroxybenzimidazolylcobamide.
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.
Daas
P J
PJ
Department of Microbiology, Faculty of Science, University of Nijmegen, The Netherlands.
Keltjens
J T
JT
Hagen
W R
WR
van der Drift
C
C
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
D008024:Ligands; D014867:Water; C051329:factor III, vitamin B 12; D014805:Vitamin B 12