From lignins to tannins: forty years of enzyme studies on the biosynthesis of phenolic compounds.

In the early 1960s, enzyme studies increasingly began to replace the common 'feeding' experiments in which labeled tracers were applied to living plants or plant parts for elucidating metabolic pathways. This advanced technique allowed to gain much deeper insights into individual details of metabolic sequences, and particularly on the previously inaccessible role of activated 'energy-rich' intermediates. Based on the author's own experience for the past 40+ years in this field, principal findings and trends elucidating the pathways to lignin and lignin precursors, acyl amides and hydrolyzable tannins (gallotannins, ellagitannins) by enzyme studies are reported.

Enzymology of gallotannin and ellagitannin biosynthesis.

Gallotannins and ellagitannins, the two subclasses of hydrolyzable tannins, are derivatives of 1,2,3,4,6-penta-O-galloyl-beta-D-glucopyranose. Enzyme studies with extracts from oak leaves (Quercus robur, syn. Quercus pedunculata; Quercus rubra) and from staghorn sumac (Rhus typhina) revealed that this pivotal intermediate is synthesized from beta-glucogallin (1-O-galloyl-beta-D-glucopyranose) by a series of strictly position-specific galloylation steps, affording so-called 'simple' gallotannins, i.

Ellagitannin biosynthesis: laccase-catalyzed dimerization of tellimagrandin II to cornusiin E in Tellima grandiflora.

An enzyme has been purified from leaves of the weed Tellima grandiflora (fringe cups, Saxifragaceae) that catalyzed the O2-dependent oxidation of the monomeric ellagitannin, tellimagrandin II, to a dimeric derivative, cornusiin E. The apparently homogeneous enzyme preparation had a Mr of ca. 160,000 (with four subunits of Mr 40,000), a pH-optimum and an isoelectric point at pH 5.

Biosynthesis of the dimeric ellagitannin, cornusiin E, in Tellima grandiflora.

First evidence for the in vitro synthesis of a dimeric ellagitannin has been obtained with cell-free extracts from the weed Tellima grandiflora (fringe cups, Saxifragaceae). Partially purified enzyme preparations from leaves of this plant catalyzed the oxidation of 1,2,3,4,6-pentagalloyl-beta-D-glucose to the monomeric ellagitannin, tellimagrandin II, followed by oxidative coupling of two units of this intermediate to yield a dimeric derivative. Chemical degradation, MALDI-TOF mass spectrometry, 1H and 13C nuclear magnetic resonance, and CD spectroscopy were employed to identify this enzyme reaction product as cornusiin E which is characterized by a (S)-valoneoyl bridge between glucose-positions 2, 4' and 6'.

Oxidation of pentagalloylglucose to the ellagitannin, tellimagrandin II, by a phenol oxidase from Tellima grandiflora leaves.

A new enzyme has been isolated from leaves of the weed Tellima grandiflora (fringe cups, Saxifragaceae) that catalyzed the O(2)-dependent oxidation of 1,2,3,4,6-penta-O-galloyl-beta-D-glucopyranose to tellimagrandin II, the first intermediate in the (4)C(1)-glucose derived series of ellagitannins. CD-spectra revealed that the 4,6-O-HHDP-residue of the in vitro product had the (S)-stereoconfiguration characteristic of tellimagrandin II from natural sources. The enzyme, for which a M(r) of ca.

Gallotannin biosynthesis: two new galloyltransferases from Rhus typhina leaves preferentially acylating hexa- and heptagalloylglucoses.

Current enzyme studies on the biosynthesis of gallotannins with cell-free extracts from leaves of staghorn sumac (Rhus typhina L.) revealed the existence of two new beta-glucogallin-dependent galloyltransferases (EC 2.3.