Stereospecificity of (+)-pinoresinol and (+)-lariciresinol reductases from Forsythia intermedia.
Pinoresinol/lariciresinol reductase catalyzes the first known example of a highly unusual benzylic ether reduction in plants; its mechanism of hydride transfer is described. The enzyme was found in Forsythia intermedia and catalyzes the presumed regulatory branch-points in the pathway leading to benzylaryltetrahydrofuran, dibenzylbutane, dibenzylbutyrolactone, and aryltetrahydronaphthalene lignans. Using [7,7'-2H2]-pinoresinol and [7,7'-2H3]lariciresinol as substrates, the hydride transfers of the highly unusual reductase were demonstrated to be completely stereospecific (> 99%). The incoming hydrides were found to take up the pro-R position at C-7' (and/or C-7) in lariciresinol and secoisolariciresinol, thereby eliminating the possibility of random hydride delivery to a planar quinone methide intermediate. As might be expected, the mode of hydride abstraction from NADPH was also stereospecific: using [4R-3H] and [4S-3H]NADPH, it was found that only the 4 pro-R hydrogen was abstracted for enzymatic hydride transfer.
Chu
A
A
Institute of Biological Chemistry, Washington State University, Pullman 99163-6340.
Dinkova
A
A
Davin
L B
LB
Bedgar
D L
DL
Lewis
N G
NG
D008031:Lignin / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D010088:Oxidoreductases / Q000378:metabolism*; D010944:Plants / Q000201:enzymology*; D013237:Stereoisomerism; D013379:Substrate Specificity
D008031:Lignin; D010088:Oxidoreductases; C084968:lariciresinol reductase; C084969:pinoresinol reductase