Enzymic Synthesis of Li:gnin Precursors

Abstract

UDPglucose :coniferyl‐alcohol glucosyltransferase was isolated from cambial sap of spruce (Picea abies). An apparently homogeneous enzyme was obtained by a seven‐step procedure including dye‐ligand chromatography. The enzyme has an M_r, of about 50000 and consists of one polypeptide chain. Transferase activity is not influenced by metal ions. The enzyme shows a pronounced substrate specificity towards UDPglucose and coniferyl alcohol with K_m values of respectively 220 μM and 250 μM. The only reaction product is coniferin (coniferyl alcohol 7‐O‐β‐d‐glucopyranoside). No formation of ‘isoconiferin’ (coniferyl alcohol 1 ‐O‐β‐d‐glucoside) was detected. The reversibility of the reaction was proved by formation of [³H]UDPglucose from [³H]UDP and coniferin in the presence of the transferase. The products UDP and coniferin inhibit the reaction noncompetitively. Product inhibition patterns are consistent with a mono‐iso‐ordered bibi mechanism involving two isomeric enzyme forms.