Formation of lignans (-)-secoisolariciresinol and (-)-matairesinol with Forsythia intermedia cell-free extracts.
In vivo labeling experiments of Forsythia intermedia plant tissue with [8-14C]- and [9,9-2H2,OC2H3]coniferyl alcohols revealed that the lignans, (-)-secoisolariciresinol and (-)-matairesinol, were derived from two coniferyl alcohol molecules; no evidence for the formation of the corresponding (+)-enantiomers was found. Administration of (+-)-[Ar-3H]secoisolariciresinols to excised shoots of F. intermedia resulted in a significant conversion into (-)-matairesinol; again, the (+)-antipode was not detected. Experiments using cell-free extracts of F. intermedia confirmed and extended these findings. In the presence of NAD(P)H and H2O2, the cell-free extracts catalyzed the formation of (-)-secoisolariciresinol, with either [8-14C]- or [9,9-2H2,OC2H3]coniferyl alcohols as substrates. The (+)-enantiomer was not formed. Finally, when either (-)-[Ar-3H] or (+-)-[Ar-2H]secoisolariciresinols were used as substrates, in the presence of NAD(P), only (-)- and not (+)-matairesinol formation occurred. The other antipode, (+)-secoisolariciresinol, did not serve as a substrate for the formation of either (+)- or (-)-matairesinol. Thus, in F. intermedia, the formation of the lignan, (-)-secoisolariciresinol, occurs under strict stereochemical control, in a reaction or reactions requiring NAD(P)H and H2O2 as cofactors. This stereoselectivity is retained in the subsequent conversion into (-)-matairesinol, since (+)-secoisolariciresinol is not a substrate. These are the first two enzymes to be discovered in lignan formation.
Umezawa
T
T
Commonwealth Center for Wood Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0323.
Davin
L B
LB
Lewis
N G
NG
D002072:Butylene Glycols / Q000378:metabolism*; D002474:Cell-Free System; D002851:Chromatography, High Pressure Liquid; D005663:Furans / Q000378:metabolism*; D017705:Lignans; D008031:Lignin / Q000378:metabolism*; D013058:Mass Spectrometry; D010944:Plants / Q000378:metabolism*; D013237:Stereoisomerism
D002072:Butylene Glycols; D005663:Furans; D017705:Lignans; C068935:matairesinol; D008031:Lignin; C060283:secoisolariciresinol