Purification and characterization of the enzymes of fructan biosynthesis in tubers of Helianthus tuberosus Colombia .2. Purification of sucrose:sucrose 1-fructosyltransferase and reconstitution of fructan synthesis in vitro with purified sucrose:sucrose 1-fructosyltransferase and fructan:fructan 1-fructosyltransferase

Sucrose:sucrose 1-fructosyltransferase (1-SST), an enzyme involved in fructan biosynthesis, was purified to homogeneity from tubers of Helianthus tuberosus that were harvested in the accumulation phase. Gel filtration under native conditions predicted a molecular mass of about 67 kD. Electrophoresis or gel filtration under denaturing conditions yielded a 27- and a 55-kD fragment. 1-SST preferentially catalyzed the conversion of sucrose into the trisaccharide 1-kestose (GF(2)). Other reactions catalyzed by 1-SST at a lower rate were self-transfructosylations with GF(2) and 1,1-nystose (GF(3)) as substrates yielding GF(3) and 1,1,1-fructosylnystose, respectively, as products. 1-SST also catalyzed the removal of the terminal fructosyl unit from both GF(2) and GF(3), which resulted in the release of sucrose and GF(2), respectively, and free Fru. The purified enzyme did not display beta-fructosidase activity. An enzyme mixture of purified 1-SST and fructan:fructan 1-fructosyltransferase, both isolated from tubers, was able to synthesize fructans up to a degree of polymerization of at least 13 with sucrose as a sole substrate.