title: Biochemical characterization of ethanol-dependent reduction of furfural by alcohol dehydrogenases.
abstract: Lignocellulosic biomass is usually converted to hydrolysates, which consist of sugars and sugar derivatives, such as furfural. Before yeast ferments sugars to ethanol, it reduces toxic furfural to non-inhibitory furfuryl alcohol in a prolonged lag phase. Bioreduction of furfural may shorten the lag phase. Cupriavidus necator JMP134 rapidly reduces furfural with a Zn-dependent alcohol dehydrogenase (FurX) at the expense of ethanol (Li et al. 2011). The mechanism of the ethanol-dependent reduction of furfural by FurX and three homologous alcohol dehydrogenases was investigated. The reduction consisted of two individual reactions: ethanol-dependent reduction of NAD(+) to NADH and then NADH-dependent reduction of furfural to furfuryl alcohol. The kinetic parameters of the coupled reaction and the individual reactions were determined for the four enzymes. The data indicated that limited NADH was released in the coupled reaction. The enzymes had high affinities for NADH (e.g., K                         (                            d                         ) of 0.043 μM for the FurX-NADH complex) and relatively low affinities for NAD(+) (e.g., K                         (                            d                         ) of 87 μM for FurX-NAD(+)). The kinetic data suggest that the four enzymes are efficient "furfural reductases" with either ethanol or NADH as the reducing power. The standard free energy change (ΔG°') for ethanol-dependent reduction of furfural was determined to be -1.1 kJ mol(-1). The physiological benefit for ethanol-dependent reduction of furfural is likely to replace toxic and recalcitrant furfural with less toxic and more biodegradable acetaldehyde.
authors.affiliation: School of Molecular Biosciences, Washington State University, Life Sciences Building, Room 202, 100 Dairy Road, Pullman, WA 99164-7520, USA.
authors.forename: Qunrui
authors.initials: Q
authors.lastname: Li
authors.forename: L K
authors.initials: LK
authors.lastname: Metthew Lam
authors.forename: Luying
authors.initials: L
authors.lastname: Xun
mesh_terms: D000426:Alcohol Dehydrogenase / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D003001:Cloning, Molecular; D020118:Cupriavidus necator / Q000201:enzymology* / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D000431:Ethanol / Q000378:metabolism*; D005662:Furaldehyde / Q000378:metabolism*; D005663:Furans / Q000378:metabolism; D007218:Industrial Microbiology; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D010802:Phylogeny; D010957:Plasmids; D011550:Pseudomonas aeruginosa / Q000201:enzymology / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D016415:Sequence Alignment; D013816:Thermodynamics; D014169:Transformation, Bacterial
chemical_list: D001426:Bacterial Proteins; D005663:Furans; D007527:Isoenzymes; D011994:Recombinant Proteins; D009243:NAD; D000431:Ethanol; C012986:furfuryl alcohol; D005662:Furaldehyde; D000426:Alcohol Dehydrogenase