Biology Reference
In-Depth Information
the biosynthesis of 1,2,3,4,6-pentagalloylglucopyranose (PGG,
3
). As
often observed in higher plants, it appears, also in this case, that the
details of a biosynthetic pathway are regulated by the actual availability
of substrates, instead of theoretical enzyme specificities that are
accessible only by
in vitro
assays.
O
G
O
G
O
G
O
O
G
O
G
3
A
C
(A-E)
O
G
O
G
O
G
G
O
G
O
G
O
O
O
O
G
G
O
G
O
O
G
O
G
G
O
G
O
O
G
O
G
O
G
G
G
E
E
B, D
A
(D)
O
G
O
G
O
G
G
O
O
O
O
G
O
G
G
O
G
O
G
O
O
G
G
O
G
O
O
G
G
O
O
G
O
G
G
G
G
G
G
E
(D)
E
(D)
Octagalloylglucoses &
higher substituted gallotannins
Fig. 3.7 Metabolic routes from pentagalloyl-β-
D
-glucopyranose (
3
) to “complex”
gallotannins in sumac leaves. Main transitions are indicated by bold arrows, minor
reactions by thin arrows. Newly introduced galloyl groups are marked by square boxes.
Properties of galloyltransferases catalyzing these reactions have been described by
Niemetz and Gross, 1999 (enzyme A)
,
Niemetz and Gross, 2001 (enzyme B), Niemetz
and Gross, 1998 (enzyme C), Fröhlich
et al.
, 2002 (enzymes D, E). Bold letters represent
major enzyme activities, minor activities are symbolized by plain letters in parentheses.
G
= Galloyl;
G
►
G
=
meta
-digalloyl residues.
3.6 The Side Route to Gallotannins
The polyester 1,2,3,4,6-pentagalloylglucopyranose (PGG,
3
) occupies a
pivotal role in the metabolism of hydrolyzable tannins as this compound
marks the point where the routes to gallotannins and ellagitannins
