FRUCTOSYLTRANSFERASE ACTIVITIES FROM LOLIUM-RIGIDUM GAUDIN

A partial separation of sucrose: sucrose fructosyltransferase (SST) activity from invertase activity extracted from leaves of Lolium rigidum Gaudin was achieved by gel filtration. The SST activity was purified 54-fold with a ratio of SST activity to invertase activity of 1.1:1. The partially purified SST activity eluted with an apparent molecular mass of about 68000, had an optimum pH of 5-5 and a K(m) of 0.12 m. When incubated with sucrose concentrations ranging from 10 to 600 mm the partially purified SST activity produced mainly 1-kestose and some 6-kestose (10-15% of trisaccharide produced). SST and invertase activities declined during storage at -25-degrees-C with invertase activity declining at a faster rate. After the loss of invertase activity in storage, the partially purified SST activity synthesized only 1-kestose. When incubated with 1-kestose the partially purified SST activity synthesized neokestose (1.9 nkat ml-1), nystose (2.2 nkat ml-1) and an unidentified tetrasaccharide (1.4 nkat ml-1) indicating that the fructosyltransferase preparation also had FFT-like activity. The partially purified invertase had significant sucrose-hydrolyzing activity (25 nkat ml-1) and contained no measurable SST activity when incubated with 10-400 mm sucrose, but produced trisaccharide (1-kestose and 6-kestose, ratio 1.5:1) when incubated with 600 mm sucrose. L. rigidum does not normally accumulate 6-kestose. The optimum pH of the sucrose-hydrolyzing activity was 4.5 and the optimum pH of the fructosyltransferase activity of the invertase preparation was 5.5. The partially purified invertase did not have significant FFT-like activity. The results support the hypothesis that SST activity synthesizes only 1-kestose, which is a key intermediate in the synthesis of fructan in L. rigidum.