Aj. Cairns et Je. Ashton, FRUCTAN BIOSYNTHESIS IN EXCISED LEAVES OF LOLIUM-TEMULENTUM L .6. OPTIMIZATION AND STABILITY OF ENZYMATIC FRUCTAN SYNTHESIS, New phytologist, 126(1), 1994, pp. 3-10
A crude enzyme preparation from excised, illuminated leaves of Lolium
temulentum L. catalyzed the de novo synthesis of fructan of apparent d
egree of polymerization 3-20. In the absence of sucrose, the fructan s
ynthetic activity (FSA) was labile at temperatures above 10 degrees C,
but could be stored at 5 degrees C for 6 h with the loss of only 20%
of the initial activity. Sucrose stabilized the FSA such that high rat
es of fructan synthesis continued for at least 6 h at 30 degrees C. By
comparison, in the absence of sucrose 80% of the FSA was lost in 2 h
at 30 degrees C. The FSA was maximal at pH 6.0 in citrate-phosphate bu
ffer and at 43 degrees C. It was not possible to saturate the FSA even
at 1500 mol m(-3) sucrose, or to calculate meaningful kinetic paramet
ers for enzymatic fructan synthesis. 1500 mol m(-3) sucrose was the hi
ghest substrate concentration practically feasible and imposed an arbi
trary maximum concentration for use in enzyme assays. Pyridoxal-hydroc
hloride was found to reduce invertase activity by 40%, but also inhibi
ted FSA by 20% at 1500 mol m(-3) sucrose and pH 6.0.