Fructosyl transferase activity in the tissue‐macerating preparation, pectolyase Y‐23*: physiological role of fructosyl transfer in Aspergillus and significance for studies of fructan synthesis in grasses

Abstract

summaryPectolyase Y‐23 is a commercially available plant tissue‐macerating preparation derived from culture filtrates of Aspergillus japonicus. When incubated with 600 mol m−3 sucrose at pH 5.5 and 30 °C, pectolyase catalyzed the rapid synthesis of oligofructans. During a 5 h incubation, 53 % of the original mass of substrate was converted to oligofructan. Thin layer chromatography (TLC) indicated that the predominant products were the trisaccharide isokestose and the tetrasaccharide nystose, though fructans of up to degree of polymerization (DP) 6 were also detected. The synthesis of oligofructan was accompanied by the release of large amounts of free glucose, but free fructose was a minor product of the reaction, indicating a low activity of invertase in the preparation. The fructan products were stable during incubation periods of up to 24 h showing the absence of fructan hydrolase in the pectolyase preparation. The pectolyase fructosyl transferase reaction was similar to reactions catalyzed by enzymes from other Aspergillus spp. In particular, the reaction strongly resembled the industrial synthesis of the commercial sugar product, Neosugar.The substrate concentration kinetics of glucose release from sucrose by pectolyase were determined and the parameters Vmax and Km for fructosyl transfer were calculated as 218 nkat mg−1 of pectolyase and 67 mol m−3 sucrose respectively. The fructosyl transferase was partially purified by quaternary‐amine ion exchange chromatography.Pectolyase Y‐23 has previously been used in the preparation of a fructosyl transferase derived from barley leaf protoplasts. The pectolyase fructosyl transferase exhibited similar properties to those reported for the barley enzyme.