S. Pestlin et al., KINETICS AND EQUILIBRIA OF CONDENSATION-REACTIONS BETWEEN MONOSACCHARIDE PAIRS CATALYZED BY ASPERGILLUS-NIGER GLUCOAMYLASE, Biotechnology and bioengineering, 56(1), 1997, pp. 9-22
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.