HYDROLYSIS OF BARLEY (1-]3),(1-]4)-BETA-D-GLUCAN BY A CELLOBIOHYDROLASE-II PREPARATION FROM TRICHODERMA-REESEI

The molecular weight of commercial barley beta-glucan was 250,000 as d etermined by dual angle laser light scattering. H-1 NMR analysis showe d the polymer to contain 29% (1 --> 3)-linkages and 71% (1 --> 4)-link ages. The barley beta-glucan was readily hydrolysed by a highly purifi ed cellobiohydrolase II (CBHII) preparation from Trichoderma reesei. N MR data demonstrated that the cellulase preparation degraded only (1 - -> 4)-linkages in the P-glucan chain. Neither internal G(1 --> 3)G(1 - -> 4)G nor reducing end G(1 --> 3)C(1 --> 4)G(1 --> 4)G sequences were hydrolysed. The main hydrolysis products were: cellobiose, beta-D-Glc p-(1 --> 3)-beta-D-Glcp-(1 --> 4)-D-Glcp, beta-D-Glcp-(1 --> 3)-beta-D -Glcp-(1 --> 4)-beta-D-Glcp-(1 --> 4)-D-Glcp and beta-D-Glcp-(1 --> 4) -beta-D-Glcp-(1 --> 3)-beta-D-Glcp-(1 --> 4)-beta-D-Glcp. Statistical models of the glucan linkage sequence were fitted to the relative frag ment concentrations after CBHII and lichenase degradations. The hydrol ysate compositions are well reproduced by a second order Markov chain. All degradation data are consistent with the assumed degradation mech anisms of the two enzymes, including the hypothesis that hydrolysis by CBHII depends on the glycosidic bond orientation.