Liquid Chromatography Applied to Olisgosaccharide Fractionation

Stereochemistry of the hydrolysis reaction catalyzed by endoglucanase Z from Erwinia chrysanthemi

Endoglucanase Z from the phytopathogenic bacterium Erwinia chrysanthemi (strain 3937) was purified by affinity chromatography on microcrystalline cellulose Avicel PH101. A kinetic characterization using p-nitrophenyl beta-D-cellobioside and p-nitrophenyl beta-D-lactosde as substrates was conducted: endoglucanase Z exhibited Km values of 3 mM and 7.5 mM and Vm values of 129 and 40 nmol.min-1.mg-1 towards p-nitrophenyl beta-D-cellobioside (kcat = 0.1 s-1) and p-nitrophenyl beta-D-lactoside (kcat = 0.03 s-1), respectively). The hydrolysis of cellotetraitol by endoglucanase Z was followed by HPLC and 1H NMR. Results show that cellobiitol and beta-cellobiose are initially formed, demonstrating that the enzyme is acting by a molecular mechanism retaining the anomeric configuration. This suggests the involvement of a glycosyl-enzyme intermediate.

Evaluation of the liquid chromatographic separation of monosaccharides, disaccharides, trisaccharides, tetrasaccharides, deoxysaccharides and sugar alcohols with stable cyclodextrin bonded phase columns

Both alpha- and beta-cyclodextrin (CD) bonded phase columns were evaluated for their ability to separate carbohydrates and related molecules. Chromatographic data on approximately 50 solutes are reported. Mobile phases consisting of acetonitrile-water or acetone-water produce the best separations. Separations could be run in isocratic or gradient modes. The alpha-CD column produced slightly more efficient separations than the beta-CD column. Both cyclodextrin columns seemed to be more efficient and selective than alkylamine and ion-exchange columns. The stability and reproducibility of the CD columns were excellent and showed little deterioration after several thousand injections. The retention of saccharides on CD bonded phases seems to be related to the number of available hydroxy groups per solute and to the size of the solute. Analysis times and detection sensitivity are discussed.