Some Properties of β-Fructof uranosidase from Arthrobacter sp. K-1 and Its Application

Abstract

Arthrobacter sp. K-1 isolated from soil, produces β-fructofuranosidase. The enzyme had a molecular weight of 52, 000, and isoelectric point of 4.3. This enzyme was most active at pH 6.5-6.8 and at 55°C and stable up to 45°C at pH 6.5 for 30 min of incubation, and from pH 5.5 to 10.0 at 40t in 2 hr of incubation. The enzyme hydrolyzed sucrose, erlose, raffiinose, xylosyl-fructoside, neokestose, and stachyose, in this order, but hardly hydrolyzed 1-kestose and nystose. The enzyme catalyzed both transfructosylation and hydrolytic action, when it was incubated with sucrose alone. But in the presence of a suitable acceptor such as 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, malto-triose, 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 suggar alcohols, and some glycosides acted as acceptors. The require-ment for an acceptor of the transfructosylation by the enzyme is that the saccharide 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 non-reducing 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. The enzyme is useful to synthesize heterooligosaccharide containing fructose. The lactosu-crose 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 Bifidobacterium. The admin-istration of the saccharide improved the intestinal bacterial flora.