抄録
Arthrobacter sp. K-1 β-fructofuranosidase catalyzed both transfructosylation and hydrolytic action, when it was incubated with sucrose alone. But in the presence of a suitable acceptor such as D-xylose and lactose, the enzyme catalyzed mostly transfructosylation and transferred the fructose residue preferentially to the acceptor. The enzyme had wide acceptor specificities. D-Xylose, D-galactose, L-sorbose, D- and L-fucose, D- and L-arabinose, maltose, isomaltose, cellobiose, lactose, melibiose, xylobiose, maltotriose, methyl β-glucoside, and galactoside were efficient acceptors in the transfructosylation. On the other hand, D-ribose, L-rhamnose, D-mannose, 2-deoxy-D-glucose, D-galactosamine, D-galacturonic acid, and 1-kestose were not efficient acceptors. Various primary alcohols, polyhydric alcohols including some sugar alcohols, and some glycosides acted as acceptors, but secondary alcohols with one hydroxyl group such as 2-propanol and 2-butanol were not effective as acceptors. The requirement for an acceptor of the transfructosylation by the enzyme is that the structure must have free hydroxyl groups of the equatorial bonds at C2 and C3 on 4C1 or 1C4 conformation. The main transfer products to aldoses and ketoses by the enzyme were nonreducing oligosaccharides, which had a fructofuranosyl residue bounded to their hemiacetal hydroxyl groups. In the case of D-galactose and L-arabinose, the enzyme produced not only non-reducing oligosaccharides, but also reducing oligosaccharides, identified as 3-O-β-D-fructofuranosyl-D-galactose and 4-O-β-D-fructofuranosyl-L-arabinose, respectively. In the cases of glycosides such as methyl a-D-glucoside, the enzyme transferred the fructofuranosyl residue only to C6 hydroxyl group. This enzyme is useful to synthesize heterooligosaccharide containing fructose. The lactosucrose has been produced on industrial scale by using this enzyme, and supplied in large quantities for food applications. The lactosucrose is not digestible in the human small intestine, but it is fermented by human intestinal microorganisms, especially by Bif dobacterium. The administration of the saccharide will improve the intestinal bacterial flora.
