Purification and characterization of the enzymes of fructan biosynthesis in tubers of Helianthus tuberosus 'Colombia': I. Fructan: fructan fructosyl transferase

Fructan: fructan fructosyl transferase (FFT), one of the enzymesinvolved in the synthesis of ß-2,1 linked fructosepolymers has been purified 205-fold from tubers of Helianthustuberosus harvested in the accumulation phase. The molecularweight of the native as well as the SDS-denatured protein isapproximately 70 kDa. On IEF, the protein was separated intofive 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 Q10value between 25 and 5° C was 1.14. FTT catalysed the self-transferof fructosyl groups with GF₂, GF₃, GF₄ or GF₅ as substrate andacceptor. The rate of elf-transfer with both GF₂ and GF₃ increasedlinearly with substrate concentration up to 100 mol m^–3and was still not saturated at 600 and 300 mol m^–3, respectively.FFT was unable to hydrolyse GF or to catalyse the self-transferwith GF but could mediate the transfer of fructosyl units frominulin on to GF. Key words: Fructan: fructan fructosyl transferase, Helianthus tuberosus, Jerusalem artichoke, purification, kinetics