Agronomy Department, Purdue University, West Lafayette, Indiana 47907.
Plant Physiol. 1992 Sep;100(1):199-204. doi: 10.1104/pp.100.1.199.
Fructans are the major storage carbohydrate in vegetative tissues of wheat (Triticum aestivum L.). Fructan:fructan fructosyl transferase (FFT) catalyzes fructosyl transfer between fructan molecules to elongate the fructan chain. The objective of this research was to isolate this activity in wheat. Wheat (cv Caldwell) plants grown at 25 degrees C for 3 weeks were transferred to 10 degrees C to induce fructan synthesis. From the leaf blades kept at 10 degrees C for 4 days, fructosyl transferase activity was purified using salt precipitation and a series of chromatographic procedures including size exclusion, anion-exchange, and affinity chromatography. The transferase activity was free from invertase and other fructan-metabolizing activities. Fructosyl transferase had a broad pH spectrum with a peak activity at 6.5. The temperature optimum was 30 degrees C. The activity was specific for fructosyl transfer from beta(2-->1)-linked 1-kestose or fructan to sucrose and beta(2-->1) fructosyl transfer to other fructans (1-FFT). Fructosyl transfer from oligofructans to sucrose was most efficient when 1-kestose was used as donor molecule and declined as the degree of polymerization of the donor increased from 3 to 5. 1-FFT catalyzed the in vitro synthesis of inulin tetra- and penta-saccharides from 1-kestose; however, formation of the tetrasaccharide was greatly reduced at high sucrose concentration. 6-Kestose could not act as donor molecule, but could accept a fructosyl moiety from 1-kestose to produce bifurcose and a tetrasaccharide having a beta(2-->1) fructose attached to the terminal fructose of 6-kestose. The role of this FFT activity in the synthesis of fructan in wheat is discussed.
果聚糖是小麦（Triticum aestivum L.）营养组织中的主要储存碳水化合物。果聚糖：果聚糖果糖基转移酶（FFT）催化果聚糖分子间的果糖基转移，从而延长果聚糖链。本研究的目的是从小麦中分离这种活性。在 25°C 下生长 3 周的小麦（cv Caldwell）植物被转移到 10°C 以诱导果聚糖合成。从在 10°C 下保持 4 天的叶片中，使用盐沉淀和一系列色谱程序（包括大小排阻、阴离子交换和亲和色谱）纯化果糖基转移酶活性。该转移酶活性与转化酶和其他果聚糖代谢活性无关。果糖基转移酶具有广泛的 pH 谱，最适 pH 为 6.5。最适温度为 30°C。该活性特异性地从β（2-->1）-连接的 1-蔗果三糖或果聚糖向蔗糖和β（2-->1）果糖基转移到其他果聚糖（1-FFT）进行果糖基转移。当以 1-蔗果三糖为供体分子时，寡果聚糖向蔗糖的果糖基转移最有效，而供体聚合度从 3 增加到 5 时，果糖基转移效率降低。1-FFT 可催化 1-蔗果三糖体外合成菊粉四糖和五糖；然而，在高蔗糖浓度下，四糖的形成大大减少。6-蔗果三糖不能作为供体分子，但可以从 1-蔗果三糖接受果糖基部分，产生分叉和一个四糖，该四糖的末端果糖连接到 6-蔗果三糖的末端果糖上。讨论了这种 FFT 活性在小麦果聚糖合成中的作用。
