SUMMARYA commercially available invertase preparation from yeast was analysed by native gel electrophoresis and shown to contain the large and small forms of yeast invertase but no specific fructosyl transferase. Both invertase isoforms catalysed the synthesis of the trisaccharides isokestose, neokestose and kestose from 600 mol m"^ sucrose at pH 5.The hydrolytic and fructosyl transferase properties of the unfractionated invertase preparation were analysed under conditions similar to those used for the analysis of sucrose : sucrose fructosyl transferase (SST) from grasses. The sucrose concentration kinetics of the transferase gave a K^ of between 224-308 mol m"^ which is similar to that reported for SST from graminaceous and other plant species. The sucrose K^ of the hydrolase was estimated at between 11-34 mol m"^.The transferase and hydrolase activities of yeast invertase could be distinguished on the basis of their responses to reaction temperature and pH, and in these respects, the data reproduced the results of grass SST studies. These observed differences in properties can be explained in terms of changes in reaction sucrose concentration and the differential kinetic properties of the hydrolase and transferase activities.The two activities could not be distinguished on the basis of their temperature-stability characteristics or their responses to pyridoxal HCl. Pyridoxal HCl was shown to cause acidification of enzyme reactions and the direct effects of this compound on the transferase and hydrolase activities were thus difficult to interpret.The results are discussed with respect to the evidence for separate SST and invertase activities in mixed enzyme systems derived from grass tissues.

SUMMARYExcised leaves of oat, wheat, barley and timothy were illuminated continuously for 24 h and .shown to accumulate both sucrose and fructan. The fructan complements of the four species were compared with the well-characterized pattern from leaves of L. temulentum L. by thin-layer chromatography (TLC). Wheat and barley had similar patterns of oligosaccharides, accumulating isokestose, kestose and a range of oligofructans up to an apparent degree of polymerization (DP) of 10. Oat leaves accumulated neokestose in addition to kestose and isokestose. The oligofructans of oat also extended up to DP 10, though the pattern was more complex than that of wheat and barley Timothy leaves accumulated fructan predominantly of apparent DP > 16 and little smaller oligofructan. Analysis of concentrated carbohydrate extracts showed isokestose, kestose and a ladder of oligofructans of apparent DP in the range 4 to > 20 in induced timothy leaves. The results showed that leaves of each grass accumulated a distinct and species-specific pattern of fructan.Concentrated enzyme preparations from illuminated leaves of each species were incubated at 30 C with 400 mol m-' sucrose at pH 4-6 in the presence of 16 mol m-» pyridoxa! hydrochloride. The preparations catalyzed the de novo net synthesis of trisaccharides and larger ol.gofructans at rates approximating to rates of soluble carbohydrate accumulation in the tissue. On TLC, the enzyme products exhibited a marked resemblance to the complement of native fructan in the source tissue. The data demonstrate that the species specihc.ty of the tructan complement can be explained by the properties of synthetic enzyme(s) alone, and is not dependent upon structural features of intact cells or tissues.The established view of fructan synthesis holds that the polymerizing enzyme, fructan: fructan fructosyl transferase (FFT) is inhibited by sucrose. The enzymes from all five grass species manufactured fructans of DP > 3 in the presence of high concentrations of sucrose (above 200 molm"^). Hence the properties of these grass fructan polymerases differ from those of FFT.

SUMMARY A crude enzyme preparation from excised illuminated leaves of Lolium temulentum L. catalyzed the de novo synthesis of fructan of apparent degree of polymerization 3–20. In the absence of sucrose, the fructan synthetic activity (FSA) was labile at temperatures above 10 °C, but could be stored at 5 °C for 6 h with the loss of only 20% of the initial activity. Sucrose stabilized the FSA such that high rates of fructan synthesis continued for at least 6 h at 30 °C. By comparison, in the absence of sucrose 80% of the FSA was lost in 2 h at 30 °C. The FSA was maximal at pH 6·0 in citrate‐phosphate buffer and at 43 °C. It was not possible to saturate the FSA even at 1500 mol m−3 sucrose, or to calculate meaningful kinetic parameters for enzymatic fructan synthesis. 150 mill m−3 sucrose was the highest substrate concentration practically feasible and imposed an arbitrary maximum concentration for use in enzyme assays. Pyridoxal‐hydrochloride was found to reduce invertase activity by 40%, but also inhibited FSA by 20% at 1500 mol −3 sucrose and pH 6.0.