Purification and characterization of the enzymes of fructan biosynthesis in tubers of Helianthus tuberosus ‘Colombia’

Fructan: fructan fructosyl transferase (FFT), one of the enzymes involved in the synthesis of β-2,1 linked fructose polymers has been purified 205-fold from tubers of Helianthus tuberosus harvested in the accumulation phase. The molecular weight of the native as well as the SDS-denatured protein is approximately 70 kDa. On IEF, the protein was separated into five molecular species with pl values between pH 4.5–5.0. The optimum pH for fructosyl transfer activity was between 5.5–7.0. Temperature optimum was in the range of 25-35° C; the Q10 value between 25 and 5° C was 1.14. FTT catalysed the self-transfer of fructosyl groups with GF2, GF3, GF4 or GF5 as substrate and acceptor. The rate of elf-transfer with both GF2 and GF3 increased linearly with substrate concentration up to 100 mol m−3 and was still not saturated at 600 and 300 mol m−3, respectively. FFT was unable to hydrolyse GF or to catalyse the self-transfer with GF but could mediate the transfer of fructosyl units from inulin on to GF.