The enzyme sucrose: sucrose 1-fructosyltransferase was partially purified from barley leaf growth zones. Four
steps (ammonium sulphate precipitation and polyethylene glycol precipitation, followed by chromatography on
Concanavalin A-sepharose and hydroxylapatite) yielded a 35-fold purification. The resulting preparation of 1-SST which still contained a number of different activities related to fructan metabolism, was subjected to
preparative isoelectric focusing, and sections of the gel were analysed individually for 1-SST and related activities,
using sucrose and 1-kestose as substrates. This procedure yielded a 196-fold purification and revealed the presence
of two isozymes of 1-SST with pI values of 4.93 and 4.99, as determined by analytical isoelectric focusing of the
corresponding fractions. Both isozymes produced glucose and 1-kestose when incubated with sucrose. In addition,
small amounts of 6-kestose and tetrasaccharides were formed. In particular, one of the two 1-SST isozymes
yielded fructose when incubated with 1-kestose, indicating that it also acts as a fructan exohydrolase. The other
isozyme exhibited less fructan exohydrolase activity. Nystose was also degraded by the fructan exohydrolase
activity but less than 1-kestose, whereas 6-kestose was not a substrate for the enzyme. Incubation of both 1-SSTs
with different concentrations of sucrose showed that the enzyme was not saturated even at 500 mM. As for the
barley sucrose: fructan 6-fructosyltransferase, both isozymes of 1-SST yielded two polypeptide bands of
molecular weight 50 and 22 kDa upon sodium dodecylsulphate polyacrylamide gel electrophoresis, suggesting
their close relationship to invertase (composed of two subunits of similar size), as previously reported for other
plants.