Borohydride reactivity of cellulose reducing ends

A comparative study of the kinetics of sodium borohydride reduction of reducing ends on model celluloses and soluble cellooligosaccharides (COS) was conducted to better understand the nature of reducing ends encountered by reducing end-specific exo-acting cellobiohydrolases. Apparent second-order rate constants for the reduction of glucose, COS (degree of polymerization from two to five) and typical microcrystalline and amorphous cellulose substrates were determined. In general, rate constants for the reduction of the cellulose-associated borohydride-accessible reducing ends were similar to those describing the reduction of the COS. Thus, no significant differences were observed between the amorphous celluloses and COS. The reactivity of the microcrystalline cellulose preparation was found to be significantly (p=0.0018) lower (∼20%) than that of the reference COS. All of the celluloses and COS had significantly lower rates of reaction than glucose (p<0.0001). The results indicate that the reagent-accessible reducing ends on typically employed amorphous cellulose substrates behave similar to those of cellooligosaccharides free in solution.