木聚糖酶TAXI型抑制蛋白的研究进展

木聚糖酶是一种重要的半纤维素酶,广泛用于饲料工业。近年来在小麦中发现一类能抑制木聚糖酶活性的蛋白,这类抑制蛋白可能会对木聚糖酶的应用效果产生影响。目前发现在不同的谷物中共存在2种类型的木聚糖酶抑制蛋白,根据其结构的不同,分为TAXI型(triticum aestivum xylanase inhibitor)和XIP型(xylanase inhibi-tor protein)。本文主要简述了TAXI型抑制蛋白的分子结构、抑制特性和活性影响因素等方面的研究进展,对于深入研究木聚糖酶及其活性影响因子,充分开发利用我国饲料资源和促进畜牧业生产可持续发展具有重要现实意义。     

木聚糖酶抑制蛋白的研究进展

简要介绍了三类木聚糖酶抑制蛋白的分子结构、抑制特性及其在谷物中的抗病防御作用。     

木聚糖酶TAXI型抑制剂及基因工程研究

谷物中存在2种类型的木聚糖酶抑制剂,根据其结构的不同可分为TAXI型和XIP型。本文主要简述了木聚糖酶TAXI型抑制剂对木聚糖酶的抑制特性及其基因工程研究。     

Effects of fungicide treatment,N-fertilisation and harvest date on arabinoxylan,endoxylanase activity and endoxylanase inhibitor levels in wheat kernels

Fungicide treatment had a significant impact on endoxylanase activity and XIP levels, but did not affect arabinoxylan (AX) and TAXI levels. The different response of TAXI and XIP type inhibitors to fungicide treatment is interesting. N-fertilisation did not affect AX levels, but significantly increased TAXI and XIP type inhibitor levels. Wheat-associated microbial endoxylanase activity levels were also affected by nitrogen supply, but levels of the endogenous enzyme did not change, except when sprouting occurred. The weather conditions before harvest had no influence on total AX (TOT-AX) and inhibitor levels, but had a large impact on both microbial and endogenous endoxylanase activity and water extractable AX (WE-AX) levels. Under most conditions, endoxylanase activity levels were related to those of α-amylases, liquefaction numbers (LN) and specific weights. WE-AX levels were often weakly but significantly correlated with endoxylanase activity levels, indicating that it is possible that part of the WE-AX in wheat originates from AX degradation by endoxylanases in the field. These results clearly indicate that agronomic circumstances significantly affect the levels of AX, endoxylanases and their inhibitors in wheat, and consequently could affect wheat quality.     

Effects of genotype,harvest year and genotype-by-harvest year interactions on arabinoxylan,endoxylanase activity and endoxylanase inhibitor levels in wheat kernels

The effects of genotype, harvest year and their interaction on the levels of arabinoxylans (AX), endoxylanases and endoxylanase inhibitors in wheat were studied using 14 varieties grown in three successive growing periods with diverse climatological conditions. Relations with more commonly evaluated wheat characteristics such as yield, thousand kernel weight, specific weight, protein level, Hagberg falling number (HFN) and α-amylase activity level were examined. Water extractable arabinoxylan (WE-AX) levels in wheat varied much more than total arabinoxylan (TOT-AX) levels. This variability was mainly genetically determined, but harvest year also had an important effect. Total endoxylanase activity levels varied more than a factor of 20 between the different wheat samples. Endogenous endoxylanases typically accounted for only 10–15% of this activity, while wheat-associated microbial endoxylanases accounted for the remaining 85–90%. However, when preharvest sprouting occurred, the contribution of endogenous endoxylanases could sometimes amount to over 40% of this total activity. Endogenous endoxylanase activity levels were mainly determined by the interaction of genotype and harvest year, while wheat-associated microbial endoxylanase activity levels were predominantly determined by genotype alone. Endogenous and microbial endoxylanase activity levels were strongly correlated, suggesting that wheat varieties which are susceptible to preharvest sprouting are often also susceptible to microbial contamination. The TAXI and XIP-type endoxylanase inhibitor levels varied by a factor of 8 and 1.8, respectively. They were mainly determined by genotype and were rather similar in the different growing periods.     

Variation in the levels of the different xylanase inhibitors in grain and flour of 20 French wheat cultivars

A xylanase from Aspergillus aculeatus (glycoside hydrolase family 10), uninhibited by TAXI, and a xylanase from Bacillus subtilis (family 11), uninhibited by XIP-I, were selected to quantify the respective apparent levels of XIP-I and TAXI inhibitors, in flours and grains of 20 wheat varieties. The apparent TAXI amount ranged from 0.05 to 0.19 mg/g in flour (mean: 0.11 mg/g) and from 0.07 to 0.2 mg/g in grain (mean: 0.14 mg/g). The range observed for XIP-I was 0.12–0.6 mg/g in flour (mean 0.32 mg/g), and 0.21–0.56 mg/g in grain (mean: 0.41 mg/g). The inhibition profile of the xylanase from A. aculeatus by a crude inhibitor preparation suggested the presence of an additional component in wheat flour, responsible for an increase in inhibition.