Cycloinulo-Oligosaccharide Fructanotransferase : Properties and Its Reaction Products

Abstract

An extracellular enzyme from Bacillus circulans OKUMZ 31B produced cycloinulo-oligosaccharides (CFs) from inulin. The enzyme, designated as cycloinulo-oligosaccharide fructanotransferase, was purified from the cultured broth to homogeneity. The enzyme is monomeric protein having molecular weight of about 132, 000 and optimum pH is 7-7.5. The enzyme catalyzes not only cyclization but also disproportionation, coupling and hydrolyzing reactions against β-2, 1 fructan. The molecular structure of cycloinulohexaose (CF6), a main product of the enzyme reaction, was determined by X-ray crystallographic analysis. The molecule has C3 symmetry with asymmetric units of inulobiosyl moieties in which two D-fructofuranosyl residues have 4T3 conformations. The molecule has an 18-crown-6 moiety which shows the GTGTGT conformational arrangement of the six sequential -0-CH2-C-O- units . Interactions of CFs and metal ions were examined by ligand exchange chromatography . Considerable interaction between CF6 and Ba2+ was shown in H2O. In aq. 50% (v/v) methanol, CF6 interacts with Bat, Pb2+, Ag+, K+, Rb+ and Cs+. A conductometric experiment suggested that CF6 and Ba2+ form a complex in the ratio of 1 : 1 in aq. 50% (v/v) methanol.