打顶对烤烟叶片生长期间蛋白酶及含氮化合物的影响

K326生长期间进行打顶和未打顶处理,研究鲜烟叶片蛋白酶及含氮化合物的变化规律。结果表明：蛋白酶、总游离氨基酸在生长期间呈“M”型曲线变化,分别在打顶后20d和50d达到高峰,且打顶处理的烟株叶片蛋白酶含量大于未打顶处理,但总游离氨基酸与此相反。可溶性蛋白和非可溶性蛋白在生长期间呈先升高后降低的趋势,在打顶后20d左右达到最大值,随后逐渐降低,且打顶处理的烟株大于未打顶处理的烟株。     

Digestion of peptidic residues in humic substances by an alkali-stable and humic-acid-tolerant proteolytic activity in the gut of soil-feeding termites

Previous feeding experiments have shown that soil-feeding termites (Termitidae: Termitinae) preferentially mineralize the peptidic component of synthetic humic acids, but nothing was known about the mechanism involved in digestion. Here, we studied the hydrolysis of humus-stabilized peptides in gut extracts of Cubitermes orthognathus by measuring the release of radiolabel from ¹⁴C-peptide-labeled synthetic humic acids. Gut extracts exhibited proteolytic activity over a wide pH range (from 4 to 12) with a maximum at about pH 8. The highest activity was located in the gut section containing the midgut and the extremely alkaline (up to pH 12) mixed segment. Chemical hydrolysis at in situ pH (up to pH 12) was negligible. Proteolytic activity in the hindgut fluid was generally relatively low, but alkaline proteases dominated in the anterior hindgut. When compared to other alkaline proteases, the proteolytic activity of gut extracts had a higher alkali-stability and tolerance to humic acids than subtilisin and an alkaline protease of Streptomyces griseus. Gut extracts also hydrolyzed the peptidic component of synthetic humic acids more efficiently than the commercial enzymes. Together with previous results, this study strongly supports the hypothesis that soil-feeding termites mobilize and digest the peptidic component of organic nitrogen in soil humic substances by a combination of proteolytic activities and extreme alkalinity in their intestinal tract.     

Gross nitrogen mineralisation rates in pastural soils and their relationships with organic nitrogen fractions, microbial biomass and protease activity under glasshouse conditions

In this study, gross nitrogen (N) mineralisation rates were determined in six pasture soils (Fleming, Kairanga, Karapoti, Lismore, Templeton and Waikoikoi) from three different regions of New Zealand. The soils were kept under controlled soil water potential (–10 to –30 kPa) and temperature (12–20°C) conditions in a glasshouse. The gross N mineralisation rates ranged from 0.76 to 5.87 g N g^–1 soil day^–1 in the six soils and were positively correlated with the amount of amino acid-N (AA-N), ammonia-N (NH₃-N), total hydrolysable-N (TH-N), microbial biomass-carbon (MB-C), microbial biomass-N (MB-N), protease activity and organic C and N. A stepwise regression was used to generate equations that could best describe gross N mineralisation rates. Microbial biomass-carbon and AA-N were included in the equation that best described the gross N mineralisation rate:

The use of polyethylene mulches to change soil microclimate as revealed by enzyme activity and biomass nitrogen,sulphur and phosphorus

Summary The effects of white, black and clear polyethylene mulches on temporal fluctuations in protease, sulphatase and phosphatase activities and levels of available and biomass N, S and P in raised beds of soil under a strawberry crop were investigated under field conditions. During spring, summer and early autumn, clear and, to a lesser extent black, polyethylene mulch increased both maximum and minimum mean monthly temperatures over those recorded with white mulch or no mulch. During summer and autumn, soil moisture content measured at monthly intervals was higher under mulched than unmulched conditions. Levels of extractable nitrate and sulphate in soils during autumn followed the order: clear mulch = black mulch > white mulch > no mulch. However, there were no significant differences in levels of enzyme activity or concentrations of biomass N, S or P between treatments. There were significant seasonal fluctuations in estimates of biomass N, S and P, but there was no close relationship between fluctuations in any estimate. This discrepancy was attributed to errors in the chloroform fumigation technique. Enzyme activities showed significant temporal fluctuations but the three enzymes did not show similar times of minimum and maximum activity. The complexity of interactions between soil microbial and biochemical properties and nutrient availability was exemplified by the absence of a discernible relationship between seasonal fluctuations in enzyme activities and levels of biomass N, S and P and/or levels of extractable mineral N, S and P in the soil. Strawberry fruit yields and vegetative growth followed the order : clear mulch = black mulch>white mulch>no mulch. Clear, and to a lesser extent black mulch increased the percentage of total yields produced in the first 2 months of cropping.     

Studies on digestibility and digestive enzyme activities in Labeo rohita (Hamilton) juveniles: effect of microbial α-amylase supplementation in non-gelatinized or gelatinized corn-based diet at two protein levels

A 60-days feeding trial was conducted to delineate the effect of both gelatinized and non-gelatinized corn with or without supplementation with exogenous α-amylase at two dietary protein levels (35% and 28%) on dry matter digestibility, digestive enzymes and tissue glycogen content of Labeo rohita juveniles. Three hundred and sixty juveniles (average weight 10±0.15 g] were randomly distributed into 12 treatment groups with each of two replicates. Twelve semi-purified diets containing either 35% or 28% crude protein were prepared by including gelatinized (G) or non-gelatinized (NG) corn as carbohydrate source with different level of microbial α-amylase (0, 50, 100 and 150 mg kg⁻¹). The dry matter digestibility of G corn fed groups was significantly higher (P < 0.05) than that of the NG corn fed groups. Hepatosomatic index (HSI), liver glycogen and intestinal amylase activity of G starch fed groups were significantly higher (P < 0.05) than those of the NG corn fed groups. However, the reverse trend was found for gastrosomatic index (GSI), muscle glycogen and intestinal protease activity. Addition of 50 mg α-amylase kg⁻¹ feed improved the dry matter digestibility of NG starch fed groups, which was similar to that of the G corn fed groups or NG corn supplemented with 100/150 mg α-amylase kg⁻¹ feed. HSI, liver glycogen and intestinal amylase activity were significantly increased (P < 0.05) at minimum level of α-amylase in the feed (50 mg kg⁻¹) and did not increase due to further inclusion of amylase in the diet. Supplementation with α-amylase at 50 mg kg⁻¹ increased the intestinal amylase activity beyond which no significant changes were observed. Protease activity of liver and intestine was highest (P < 0.05) in higher crude protein (CP) fed groups, but protease activity of the intestine was significantly higher in the α-amylase supplemented groups. Hence, it was concluded that feed with 28% CP containing either G corn without α-amylase or NG corn with 50 mg α-amylase kg⁻¹ may be used as the alternative carbohydrate source for L. rohita juveniles.     

“东—号”剑麻蛋白酶应用于猪皮脱毛的初步研究

本文在实验室和工厂进行猪皮酶法脱毛的试验，结果表明，“东一号”剑麻蛋白酶对猪皮脱毛效果好，皮革成品质量高，为龙舌兰麻的综合利用提供了依据。     

饲料源活性肽混合物的提取及其对绵羊瘤胃微生物生长的影响

本文探讨了用鱼粉和豆粕制备活性肽的适宜条件,并以胃蛋白酶和胰蛋白酶分别水解鱼粉和豆粕制得的4种活性肽为氮源、可溶性碳水化合物为能源,采用体外法研究了不同来源的肽氮对瘤胃细菌和原虫生长的影响以及对瘤胃中蛋白酶和纤维酶活性的影响。结果表明,胃蛋白酶和胰蛋白酶分别水解鱼粉和豆粕制备活性肽的最适条件为:温度37℃,时间20 h,pH分别为2和7。来源于动物性饲料的混合肽对促进瘤胃微生物生长优于来源于植物性饲料的混合肽;分子量小于3 000 u的鱼粉肽和豆粕肽对瘤胃细菌和原虫的生长有促进作用,能提高瘤胃中蛋白酶活性,而对纤维酶活性无作用。     

Modeling growth factor activity during proinflammatory stress: methodological considerations in assessing cytokine modulation of IGF binding proteins released by cultured bovine kidney epithelial cells

The present research was conducted to model potential mechanisms through which IGFBPs might be affected by a key proinflammatory response initiating cytokine tumor necrosis factor (TNF-)-. Madin–Darby bovine kidney epithelial (MDBK) cells, known to release IGFBPs in response to several stimuli, were grown under several conditions and challenged with forskolin (F) or recombinant TNF- for 24 h. Forskolin increased IGFBP-3 gene expression and media content of BP-3 protein. TNF- increased basal and augmented F-mediated IGFBP-3 gene expression. However, TNF- effects on the measurable media content of IGFBPs were influenced by culture conditions; in the absence of added protease inhibitors (PIs) or sufficient media albumin concentration (high BSA, 1 mg/ml), the effect of TNF- was to decrease (P < 0.02) measurable IGFBPs. In the presence of PI and high BSA, media IGFBP-3 levels were shown to be increased by TNF- consistent with the gene expression data. Changes in media IGFBP-3 protease activity were examined further to explain the observed effects of TNF- on production and destruction of IGFBPs in media. When recombinant human IGFBP-3 (500 ng/ml) was added to PI-free, low BSA 100 μg/ml) media from TNF-treated MDBK cells, less than 10% of the BP-3 was recognizable by Western blot in 30 min; conversely, inclusion of High BSA and PI in media resulted in attenuation of the protease effect on the IGFBPs. The data suggest that the MDBK model of cellular response to proinflammatory stimulus is affected by culture conditions and that TNF- affects media content of IGFBPs through effects on IGFBP gene expression coupled with degradation of IGFBPs via enhanced proteolytic enzyme release.     

瘤胃微生物Fosmid文库蛋白酶活性克隆的筛选与序列分析

在日粮蛋白质的降解过程中,蛋白酶是把蛋白质水解为肽或氨基酸的关键酶,由于受到纯培养技术的影响,瘤胃内产生蛋白酶活性的细菌和各种蛋白酶的遗传信息知之甚少。本实验旨在利用蛋白酶选择性培养基从瘤胃微生物 Fosmid 文库中筛选出含蛋白酶活性的克隆子,通过生物信息学分析获得这些克隆子的遗传信息。应用脱脂乳粉和大豆蛋白粉两种蛋白酶选择性培养基,从 30 000 个克隆中筛选得到 14 个具有蛋白酶活性的活性克隆。利用福林酚试剂法检测 14 个蛋白酶克隆子的酶活力,结果表明,每个克隆子分别具有不同的蛋白质分解能力。以酪蛋白为底物的克隆子酶活力介于 0.59~2.74 U/mg 之间,以大豆蛋白粉为底物的克隆子酶活力在 0.70~7.19 U/mg 之间,而且同一克隆对于不同的底物所表现的酶活力也不同。随机挑选 10 个活性克隆进行末端测序(GenBank 登录号:JY084410~JY084429),经 Blast 比对后发现,45%的基因序列与已知编码基因无法匹配,pro10F 末端序列与金属肽酶匹配度为 54%,属于肽酶 M13 家族,且该克隆蛋白酶最适 pH 值为 7.0,为下一步研究该克隆的酶学性质和序列特征分析提供了基础资料。     

罗非鱼鱼排蛋白酶解液美拉德反应生香工艺优化研究

为了对罗非鱼鱼排蛋白酶解液美拉德反应生香工艺进行研究,以风味总体接受性为指标,对反应温度、时间、pH值、还原糖添加量4个因素采用响应面法进行多元回归拟合,优化美拉德反应条件,并用HPLC、GC-MS对反应产物进行分析。结果表明：美拉德反应最佳工艺条件为反应时间57 min,反应温度111℃,pH 6.0,还原糖（葡萄糖:木糖=2:1）添加量2.0%;反应产物中有机酸含量较反应前酶解液中有机酸含量丰富,核酸关联物较反应前多了呈味的鸟苷酸;反应产物中挥发性成分包括68种风味化合物,分别是醇类6种、醛类7种、酮类5种、芳香族7种、酯类11种、呋喃8种、吡嗪9种、吡咯1种、烃类7种、酸类5种和含硫化合物2种。罗非鱼鱼排蛋白酶解液经美拉德反应,产物呈透明红褐色,具有独特的鱼香味（香味浓郁）。