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 determined by dual angle laser light scattering. H-1 NMR analysis showed the polymer to contain 29% (1 --> 3)-linkages and 71% (1 --> 4)-linkages. The barley beta-glucan was readily hydrolysed by a highly purified cellobiohydrolase II (CBHII) preparation from Trichoderma reesei. NMR 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-Glcp-(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 fragment concentrations after CBHII and lichenase degradations. The hydrolysate compositions are well reproduced by a second order Markov chain. All degradation data are consistent with the assumed degradation mechanisms of the two enzymes, including the hypothesis that hydrolysis by CBHII depends on the glycosidic bond orientation.