KINETIC AND STEREOCHEMICAL STUDIES OF MANNO-OLIGOSACCHARIDE HYDROLYSIS CATALYZED BY BETA-MANNANASES FROM TRICHODERMA-REESEI

The two beta-mannanases from Trichoderma reesei with pI of 4.6 and 5.4 , respectively, have been characterised by NMR spectroscopy. Following the kinetics of manno-oligosaccharide degradation with complete progr ess-curve analysis the stereospecificity and degradation pattern have been delineated. It was found that degradation of mannotriose and mann opentaose proceeds with retention of the anomeric configuration. Manno triose degradation proceeds by almost random release of mannose. For m annopentaose there is initially no mannose formed showing that only th e two middle mannosidic linkages are attacked. Progress-curve analysis shows that there is preference (70%) for cleavage of mannopentaose in such a way that mannobiose is released from the reducing end. The fin al product composition from the mannotriose degradation showed that tr ansglycosylation has to be taken into account. Model calculation and p rogress-curve analysis showed that the transglycosylation rate is the fastest of all the rates in this system, 15 s(-1) compared with mannoh exaose and mannotetraose hydrolysis rates of 2 s(-1) and mannotriose h ydrolysis rate of 0.03 s(-1) at 50 degrees C.