INVERSION OF CONFIGURATION DURING HYDROLYSIS OF ALPHA-1,4-GALACTURONIDIC LINKAGE BY 3 ASPERGILLUS POLYGALACTURONASES

Endopolygalacturonases I and II (PGI and PGII) of Aspergillus niger an d an exopolygalacturonase (ExoPG) of A. tubingensis mere investigated to reveal the stereochemistry of their hydrolytic action. Reduced pent agalacturonic acid (penta-GalU-ol) and reduced trigalacturonic acid (t riGalU-ol) were used as non-reducing substrates for the enzymes. The c onfiguration of the reducing ends in the products formed in D2O reacti on mixtures was followed by H-1-NMR spectroscopy. It has been unambigu ously established that primary cleavage of pentaGalU-ol by both PGI an d PGII leads to diGalU-ol and the p-anomer of triGalUA. The primary pr oducts of hydrolysis of triGalU-ol by ExoPG were diGalU-ol and the bet a-anomer of GalUA. Thus, all three Aspergillus polygalacturonases belo ng to the so-called inverting glycanases, i.e. they utilize the single displacement mechanism of hydrolysis of the glycosidic linkage.