Characterization of redox properties of FAD cofactor of Thermotoga maritima thioredoxin reductase

Benjaminas Valiauga; Nicolas Rouhier; Jean-Pierre Jacquot; Narimantas Čėnas

doi:10.6001/chemija.v31i3.4293

Benjaminas Valiauga
Nicolas Rouhier
Jean-Pierre Jacquot
Narimantas Čėnas

DOI: https://doi.org/10.6001/chemija.v31i3.4293

Keywords: thioredoxin reductase, Thermotoga maritima, FAD, redox potential, semiquinone stability

Abstract

The fluorescence properties of FAD of Thermotoga maritima thioredoxin reductase (TmTR), taken together with the amino acid sequences and structures of similar TRs, are consistent with the interdomain rotation in the catalysis of TmTR. The standard redox potential of FAD of TmTR, –0.230 V, determined by the reactions with 3-acetylpyridine adenine dinucleotide (APAD⁺/APADH) redox couple, is close to that of E. coli TR. During the reduction of duroquinone with TmTR, the transient formation of neutral FAD semiquinone, and, possibly, FADH₂–NAD⁺ complex was observed. This shows that in spite of obligatory twoelectron (hydride)-transfer between NADH and physiological disulfide oxidants, the FAD cofactor of TmTR may exist under a stable semiquinone form.