KINETICS AND EQUILIBRIA OF CONDENSATION-REACTIONS BETWEEN MONOSACCHARIDE PAIRS CATALYZED BY ASPERGILLUS-NIGER GLUCOAMYLASE

Arabinose, fructose, galactose, myo-inositol, lyxose, mannose, ribose, and xylose were incubated individually and with glucose in the presen ce of Aspergillus niger glucoamylase at pH 4.5 and 45 degrees C. Gluco amylase condenses galactose, glucose, and mannose individually into di saccharides. It also produces mixed disaccharides when each of the eig ht carbohydrates is incubated with glucose. Many products were identif ied by gas chromatography of the derivatized reaction mixtures followe d by mass spectroscopy of the individual chromatographic peaks. Galact o-, gluco-, or mannopyranosyl rings appear to be present at the nonred ucing ends of all the disaccharides produced. Molecules linked through primary hydroxyl groups have the highest equilibrium constants of all products formed, since these bonds are thermodynamically favored. How ever, glucoamylase is capable of forming bonds with many available hyd roxyl groups, as previously demonstrated when it was incubated with gl ucose alone. Formation rates of different bonds linking different resi dues vary widely. These results demonstrate that glucoamylase has a wi de selectivity toward residues it will condense into disaccharides and toward bonds it will form between them. (C) 1997 John Wiley & Sons, I nc.