Stereoselective bimolecular phenoxy radical coupling by an auxiliary (dirigent) protein without an active center.
The regio- and stereospecificity of bimolecular phenoxy radical coupling reactions, of especial importance in lignin and lignan biosynthesis, are clearly controlled in some manner in vivo; yet in vitro coupling by oxidases, such as laccases, only produce racemic products. In other words, laccases, peroxidases, and comparable oxidases are unable to control regio- or stereospecificity by themselves and thus some other agent must exist. A 78-kilodalton protein has been isolated that, in the presence of an oxidase or one electron oxidant, effects stereoselective bimolecular phenoxy radical coupling in vitro. Itself lacking a catalytically active (oxidative) center, its mechanism of action is presumed to involve capture of E-coniferyl alcohol-derived free-radical intermediates, with consequent stereoselective coupling to give (+)-pinoresinol.
Davin
L B
LB
Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA.
Wang
H B
HB
Crowell
A L
AL
Bedgar
D L
DL
Martin
D M
DM
Sarkanen
S
S
Lewis
N G
NG
D019281:Dimerization; D005486:Flavin Mononucleotide / Q000378:metabolism; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D005609:Free Radicals; D005663:Furans / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D042845:Laccase; D017705:Lignans / Q000096:biosynthesis* / Q000737:chemistry; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D010636:Phenols / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D013237:Stereoisomerism
D005609:Free Radicals; D005663:Furans; D017705:Lignans; D010636:Phenols; D010940:Plant Proteins; D005182:Flavin-Adenine Dinucleotide; D005486:Flavin Mononucleotide; C010559:coniferyl alcohol; D010088:Oxidoreductases; D042845:Laccase; C103298:pinoresinol