Molecular approaches for enhancing sweetness in fruits and vegetables

The quality of fruits and vegetables is mainly dependant on the sweetness determined by the level of soluble sugars such as glucose, fructose and sucrose. Other fruit quality parameters include Brix content, acidity, aroma, color, size and shape. Total sugar content in fruits and vegetables is a function of genetic, nutritional, environmental and developmental factors. Understanding the factors controlling sweetness is important to design strategies for enhancing quality of fruits and vegetables. Modifying the activity of enzymes in carbohydrate metabolism such as sucrose synthase (SuSy), acid invertase, ADP-glucose pyrophosphorylase (AGPase), sucrose phosphate synthase (SPS) and sucrose transporters were found to influence carbohydrate partitioning and sucrose accumulation in sink tissues of several food crops. Plant based taste-modifying sweet proteins such as brazzein, cucurmin, mabinlin, monellin, miraculin, neoculin and thaumatin have potential application for developing transgenic plants to improve the sweetness and quality of fruits and vegetables. The present review envisages various cultural, breeding and molecular approaches used for enhancing sugar content and sweetness in fruits and vegetables.     

味精菌体蛋白替代部分蛋白质饲料对犊牛生长性能影响

试验选用初生荷斯坦犊牛18头,随机分为3组,每组6头,试验A组和试验B组分别给每头犊牛添加5%和15%比例的味精菌体蛋白,对照C组不添加味精菌体蛋白,以评定味精菌体蛋白对犊牛生长指标和健康状况的影响。结果表明:犊牛日粮中添加味精菌体蛋白替代部分蛋白质饲料,可改善饲料适口性。5%、15%味精菌体蛋白可用于断奶前不同阶段的犊牛料。     

Characterization of 11 commercial pyrethroids on the functional attributes of rat brain synaptosomes

The action of 11 commercial pyrethroids on Ca²⁺ influx and glutamate release was assessed using high-throughput functional assays with rat brain synaptosomes to better understand the mechanistic nature of pyrethroid-induced neurotoxicity and aid in the reassessment of pyrethroids in vivo. Concentration-dependent response curves for each of the non-cyano and α-cyano containing pyrethroids were determined and the data used in a cluster analysis. The previously characterized α-cyano pyrethroids that induce the CS-syndrome (cypermethrin, deltamethrin, and esfenvalerate) increased Ca²⁺ influx and glutamate release, and clustered with two other α-cyano pyrethroids (β-cyfluthrin and λ-cyhalothrin) that shared these same actions. Previously characterized T-syndrome pyrethroids (bioallethrin, cismethrin, and fenpropathrin) did not share these actions and clustered with two other non-cyano pyrethroids (tefluthrin and bifenthrin) that likewise did not elicit these actions. Our current findings indicate that pyrethroids that have an α-cyano group (with the exception of fenpropathrin) were more potent enhancers of Ca²⁺ influx and glutamate release under depolarizing conditions than pyrethroids that did not possess this functional group. The collective data set does not support the hypothesis that pyrethroids, as a class, act in a similar fashion at presynaptic nerve terminals.     

多胺代谢与缺血性心血管疾病研究进展

多胺广泛分布于生物组织和体液中,参与体内多种生理和病理过程,具有促进细胞生长、分化、增生,对维持细胞膜和线粒体的完整性,DNA和RNA结构的稳定性,以及在信号转导、基因表达、蛋白合成等方面都意义重大。多胺参与心肌缺血损伤的发生,多胺代谢失衡,鸟氨酸脱羧酶及精脒/精胺乙酰转移酶活性改变,腐胺生成增多而精胺、精脒减少,将导致继发性的心肌损伤,本文就多胺及多胺在缺血性心血管疾病研究中的意义及进展加以综述。     

利用重组枯草芽孢杆菌生产γ-氨基丁酸的研究

[目的]构建一株高产L-谷氨酸脱羧酶的重组枯芽孢杆菌B.subtilis 168/p HT01-gad A-pdx H。[方法]以枯草芽孢杆菌(Bacillus subtilis)为宿主细胞,将大肠杆菌脱羧酶基因(gad A)与其辅酶磷酸吡哆醛的再生基因(pdx H)在质粒p HT01上串联表达,构建一株高产L-谷氨酸脱羧酶的重组枯草芽孢杆菌B.subtilis 168/p HT01-gad A-pdx H。[结果]带有pdx H基因的重组菌B.subtilis 168/p HT01-gad A-pdx H催化谷氨酸生成γ-氨基丁酸(GABA)的效率明显高于B.subtilis 168/p HT01-gad A。催化反应24 h时,生成的GABA浓度达252 g/L,较对照菌株提高了61 g/L。进一步对重组菌B.subtilis 168/p HT01-gad A-pdx H全细胞转化谷氨酸生成GABA的条件进行了优化,其最优条件:转化缓冲液为p H 5.0的0.1 mol/L Tris-HCl,转化温度40℃,激活剂为5 mmol/L Ca~(2+)与5 mmol/L Mg~(2+)。在上述最优条件下,催化24 h生成的GABA浓度达327 g/L。[结论]所获得的重组菌转化效率较高,具有一定的工业化应用前景。     

定向突变谷氨酸脱羧酶及其生物合成γ-氨基丁酸的研究

γ-氨基丁酸(GABA)是一种天然存在的非蛋白质氨基酸,它由谷氨酸脱羧酶催化谷氨酸脱羧生成,作为抑制性神经递质具有广泛的应用。天然的谷氨酸脱羧酶只在酸性环境时有活性,这与菌体的生长环境不一致,不利于一步发酵法生产GABA。针对该问题,对来自大肠杆菌AS1.505的谷氨酸脱羧酶(Gad B)进行定向突变,构建了3个表达载体p ET28a(+)-Gad B、p ET28a(+)-Gad Bm1和p ET28a(+)-Gad Bm2,研究了3株重组菌生物转化谷氨酸合成GABA的情况。结果显示,在中性缓冲液中转化72 h,DE3(p ET28a(+)-Gad Bm1)和DE3(p ET28a(+)-Gad Bm2)转化合成GABA分别是对照菌DE3(p ET28a(+)-Gad B)的3.2和4.6倍。在M9培养基中培养72 h,DE3(p ET28a(+)-Gad Bm1)和DE3(p ET28a(+)-Gad Bm2)分别合成4.32 g/L和4.65 g/L GABA,比对照菌分别提高了1.17和1.34倍。实验结果证明,定向突变的Gad B能在中性p H条件下有效催化谷氨酸脱羧合成GABA。     

E.coli谷氨酸脱羧酶高产菌株选育及发酵条件研究

以普通大肠杆菌(E. coli)为出发菌株,以L-谷氨酸、溴甲酚绿(pH3.8~5.4)为筛选及指示剂,经亚硝基胍(NTG)、UV诱变处理,得到了L-谷氨酸脱羧酶活性变异菌株,其L-谷氨酸脱羧酶（GAD）活性大幅度提高,比出发菌株酶活性提高了2.22倍。优化实验显示：pH值、发酵时间、诱导剂L-谷氨酸、硫酸镁对GAD产酶有较大影响。通过对产酶发酵培养基中几种成份单因素变动及正交优化实验,对该菌株产GAD的诱导剂L-谷氨酸、营养要求和发酵条件进行了研究,优化后的发酵培养基组成为牛肉膏5 g/L,蛋白胨10 g/L,氯化钠3 g/L,L-谷氨酸0.5 g/L,葡萄糖1.5 g/L,磷酸二氢钾2 g/L,硫酸镁0.7 g/L。发酵条件是：pH6.8,接种菌龄20h,发酵时间20h。在优化条件下突变菌株GAD活性可达6790.7U,是出发菌株的2.76倍。     

草莓果实中FaSAMDC基因的克隆、生物信息学及表达分析

【目的】为明确S-腺苷甲硫氨酸脱羧酶(SAMDC)在非呼吸跃变型草莓果实成熟中的作用。【方法】以‘北农香’草莓果实为试验材料,首先通过RT-PCR克隆FaSAMDC基因,其次通过SqRT-PCR分析发育果实(小绿、大绿、褪绿、白果、片红、全红)中的FaSAMDC基因的表达量。【结果】结果表明,FaSAMDC基因含有1 116bp开放阅读框,编码371个氨基酸,含有典型的脱羧酶保守功能结构域。随着草莓的果实发育,FaSAMDC表达量呈明显下降趋势并且在白果时期达到最低值,此后随着果实着色,表达量迅速上升并且成熟期达到最高。【结论】以上研究结果证实,S-腺苷甲硫氨酸脱羧酶可能参与草莓果实的成熟调控。     

嗜热链球菌对瑞士乳杆菌发酵乳后酸化的影响

瑞士乳杆菌是潜在的功能发酵乳发酵剂,为改善瑞士乳杆菌的发酵特性,使用嗜热链球菌配合瑞士乳杆菌用于发酵乳制备。结果表明：嗜热链球菌与瑞士乳杆菌混合发酵将凝乳时间缩短了3.5 h,黏度提高了1.8 倍,改善了乳清析出和质构;嗜热链球菌的使用有效减弱了发酵乳的后酸化,贮藏20 d发酵乳的pH值仍大于4.2。为研究这一现象的原因,测定发酵乳中的活菌数、乳糖消耗量、谷氨酸脱羧酶和β-半乳糖苷酶活性,结果表明,混合发酵乳贮藏期间具有较低的谷氨酸脱羧酶和β-半乳糖苷酶活性,乳糖利用量较低,这是后酸化减弱的主要原因。与嗜     

长白落叶松几种酶活力及在种源早期选择中的应用

不同季节测定了 8个种源长白落叶松 4种酶活力 ,分析了它们与生长的关系。结果表明 ,生长快的种源过氧化物酶、多酚氧化酶活力弱 ,抗坏血酸氧化酶、谷氨酸脱氢酶活力强 ;生长慢的种源则相反 ,4种酶活力与长白落叶松的生长速率密切相关。不同季节各种酶活力的聚类分析结果相似 ,且与生长性状的聚类分析结果相一致。回归分析表明 ,过氧化物酶活力与长白落叶松的生长呈显著负相关 ,抗坏血酸氧化酶、谷氨酸脱氢酶活力与长白落叶松的生长呈显著正相关。多酚氧化酶活力与长白落叶松生长的负相关性较低。初步研究表明 ,过氧化物酶、多酚氧化酶、抗坏血酸氧化酶和谷氨酸脱氢酶可成为长白落叶松种源早期选择的生理生化指标