Edited by Ulf-Ingo Fl€ uggeThe Glucuronoyl esterases (GE) have been proposed to target lignin-carbohydrate (LC) ester bonds between lignin moieties and glucuronic acid side groups of xylan, but to date, no direct observations of enzymatic cleavage on native LC ester bonds have been demonstrated. In the present investigation, LCC fractions from spruce and birch were treated with a recombinantly produced GE originating from Acremonium alcalophilum (AaGE1). A combination of size exclusion chromatography and 31 P NMR analyses of phosphitylated LCC samples, before and after AaGE1 treatment provided the first evidence for cleavage of the LC ester linkages existing in wood.Keywords: 31 P NMR; carbohydrate esterase; lignin-carbohydrate complexes; size exclusion chromatography; spruce and birch An obstacle to intact and efficient extraction of the wood polymers cellulose, hemicelluloses and lignin may be the proposed chemical linkages connecting lignin with hemicelluloses, the so-called lignin-carbohydrate complexes (LCCs). In a lignocellulose-based biorefinery context it is therefore of interest to find mild methods, for example, enzymatic treatment, that specifically would break these lignin-carbohydrate (LC) linkages. Three types of existing covalent LC bonds have been suggested, namely benzyl ether-, ester-and phenyl glycosidic linkages [1]. The first described and most studied LC ester bond is the benzyl a-ester bond [2]. However, several more recent studies have also shown the presence of c-esters [3,4], suggested to arise due to uronosyl migrations of the linkage from the a-to the c-position [5,6].It has been proposed that glucuronoyl esterases (GE), members of the recently discovered carbohydrate esterase 15 family (CE15), could be used to target the LC ester bond between aliphatic alcohols in lignin and the 4-O-methyl-D-glucuronic acid residues of glucuronoxylans ( Fig. 1) [7,8].The first characterized GE was produced by the wood-rotting fungus Schizophyllum commune [7] and at the present time nine GEs have been characterized for their activity and kinetics on different model substrates [7][8][9][10][11][12][13][14][15][16][17][18][19][20].Cleavage of model substrates mimicking LC ester bonds has been investigated for a wide range of esters. Studies have covered simple glucuronic acid (GlcA) esters with the 'lignin moiety' being single arylalkyl units at the c-position [8,10] or at the a-position [14].