Control of xyloglucan endotransglucosylase activity by salts and anionic polymers
Control of xyloglucan endotransglucosylase activity by salts and anionic polymers
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DOI：
10.1007/s00425-004-1267-9
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发表时间：
2004-08-01
期刊：
影响因子：
4.3
通讯作者：
Fry, SC
中科院分区：
文献类型：
--
作者：
Takeda, T;Fry, SC
花椰菜小花的粗提物具有高的木葡聚糖内切转葡糖基酶（XET）活性，但在部分纯化和脱盐后这在很大程度上丧失了。活性恢复（促进高达40倍）的各种各样的无机盐和有机盐。Na+、K+和NH 4+盐的最佳浓度通常与300 mM相似。Ca 2+、Mg 2+、Al 3+和La 3+的氯化物在较低浓度（例如0.1 mM LaCl 3）下具有最佳活性，但在较高浓度（例如5 mM LaCl 3）下具有抑制作用。0.04- 0.2%w/v的一些阴离子多糖（例如阿拉伯树胶、果胶和次氯酸盐氧化的木葡聚糖）促进脱盐酶的XET活性，特别是如果还存在次优浓度的NaCl;其他的（例如高半乳糖醛酸、4-O-甲基-葡糖醛酸木聚糖和藻酸盐）是抑制性的。在拟南芥蛋白XTH 24（由昆虫细胞异源表达）的XET活性上注意到类似的离子效应;在这种情况下，羧甲基纤维素也是刺激性的。为了寻找XET活性的内源性调节剂，我们制备了花椰菜小花的冷水提取物;煮沸和离心后，上清液[煮沸的花椰菜制剂（BCP）]促进了脱盐花椰菜酶和XTH 24的XET活性。BCP中约有一半的活化剂是一种乙醇可沉淀的阴离子聚合物，其表观M-r
Crude extracts of cauliflower florets had high xyloglucan endotransglucosylase (XET) activity, but this was largely lost after partial purification and de-salting. Activity was restored (promoted up to 40-fold) by any of a wide variety of inorganic and organic salts. Optimum concentrations for Na+, K+ and NH4+ salts were typically similar to300 mM. The chlorides of Ca2+, Mg2+, Al3+ and La3+ were optimally active at lower concentrations (e.g. 0.1 mM LaCl3), but became inhibitory at higher concentrations (e.g. 5 mM LaCl3). Some anionic polysaccharides at 0.04-0.2% w/v (e.g. gum arabic, pectin and hypochlorite-oxidised xyloglucan) promoted the XET activity of de-salted enzyme, especially if a sub-optimal concentration of NaCl was also present; others (e.g. homogalacturonan, 4-O-methyl-glucuronoxylan and alginate) were inhibitory. Similar ionic effects were noted on the XET activity of the Arabidopsis protein XTH24 (heterologously expressed by insect cells); in this case carboxymethylcellulose was also stimulatory. To look for endogenous modulators of XET activity, we prepared a cold-water extract of cauliflower florets; after boiling and centrifugation, the supernatant [boiled cauliflower preparation (BCP)] promoted the XET activity of de-salted cauliflower enzyme and of XTH24. About half the activator present in BCP was an ethanol-precipitable, anionic polymer of apparent M-r