常用防腐剂对牛乳铁蛋白抗菌活性的影响

乳铁蛋白的抗菌活性常受到其他共存成分的影响。本文研究了常用防腐剂对乳铁蛋白抗菌活性的影响。在研究过程中,以大肠杆菌为实验菌株,进行了实验研究。研究表明,在牛肉膏蛋白胨培养基中,pH6.0,菌浓为106CFU/ml的条件下,乳铁蛋白对大肠杆菌的最小抑菌质量浓度为3mg/ml;苯甲酸钠、山梨酸钾、乳酸链球菌素、对羟基苯甲酸等分别与乳铁蛋白共同作用时,对乳铁蛋白的抗菌活性都有明显的影响。其中,山梨酸钾和苯甲酸钠减弱了乳铁蛋白的抗菌活性,乳酸链球菌素和对羟基苯甲酸丁酯加强了乳铁蛋白的抗菌活性。     

酶解牛乳铁蛋白制备乳铁素 B的酶解条件研究

乳铁素B是牛乳铁蛋白经胃蛋白酶酶解后所得到的最重要的抗菌肽，乳铁蛋白酶解生成乳铁素后抗菌活性大大增强。通过正交试验确立了牛乳铁蛋白酶解制备乳铁素B的最佳条件，指出在底物质量浓度为50g／L，酶与底物质量浓度比为1：30(质量比)，酶解时间为60min时所得的乳铁素质量浓度及活性较好。     

牛乳铁素结构和功能研究进展

牛乳铁蛋白是一种多功能蛋白质，具有抗菌，抗真菌，抗病毒，抗癌，抗炎，以及免疫调节作用，而这些性质都与其高度碱性的N端区域有关。这部分蛋白能在胃的酸性pH值条件下释放出来，新生成的含有25个氨基酸残基的抗菌肽被称为乳铁素。在本文中综述了该抗菌肽结构，以及结构和功能相互联系，抗菌肽和细胞膜的相互作用表明，同中性的真核细胞膜相比它更容易与带负电荷的细菌细胞膜和癌细胞膜发生反应，肽的结合破坏了膜的正常结构。对乳铁素活性非常重要的残基是色氨酸和精氨酸，他们是使蛋白质或合成抗菌肽类能自然的穿过细胞膜区域的根本原因。同时乳铁素的抗菌，抗真菌，抗病毒，抗癌性质与富含Trp／Arg的区域有关。     

乳铁蛋白和乳铁素的抗菌活性比较

牛乳铁蛋白是从牛乳中提取出来的一种铁结合性糖蛋白,牛乳铁素是从牛乳铁蛋白N-端水解下来的25个氨摹酸残荩。它们具有多种乍物学功能,其中的广谱抗菌性尤为引人注目。本实验以牛初乳中提取的乳铁蛋白及其水解产物乳铁素为研究对象,选取大肠杆菌为实验菌株,进行铁饱和乳铁蛋白和缺铁性乳铁蛋白、乳铁素对大肠杆菌生长抑制的比较研究。研究结果表明：铁饱和乳铁蛋白、缺铁性乳铁蛋白和乳铁索的最小抑菌浓度分别为6mg／ml、3mg／ml和15μg／ml,乳铁素的最小杀菌浓度为30μg／ml。乳铁蛋白水解后,经纯化获得的乳铁素,其抗菌能力较缺铁性乳铁蛋白增加200倍,较铁饱和乳铁蛋白增加400倍。     

牛乳中乳铁蛋白的纯化和抗菌活性研究

采用凝胶过滤层析和离子交换法层析分离纯化乳铁蛋白,通过SDS-PAGE和IEF-PAGE鉴定所得样品;同时利用抗菌实验(滤纸片法)进行样品的抗菌活性研究,并研究了乳铁蛋白分离纯化过程中抗菌活性的变化。结果表明,离子交换层析纯化乳铁蛋白的效果优于凝胶过滤层析,抗菌活性证实乳铁蛋白样品具有广谱抗菌作用,以蜡状芽孢杆菌为指示菌时,比活为3077.3AU/mg(试管法),纯化倍数提高了20.2倍。     

牛乳中乳铁蛋白的纯化和抗菌活性研究

采用凝胶过滤层析和离子交换法层析分离纯化乳铁蛋白,通过SDS-PAGE和IEF-PAGE鉴定所得样品;同时利用抗菌实验（滤纸片法）进行样品的抗菌活性研究,并研究了乳铁蛋白分离纯化过程中抗菌活性的变化。结果表明,离子交换层析纯化乳铁蛋白的效果优于凝胶过滤层析,抗菌活性证实乳铁蛋白样品具有广谱抗菌作用,以蜡状芽孢杆菌为指示菌时,比活为3077.3AU/mg（试管法）,纯化倍数提高了20.2倍。      

乳铁素B的抗菌活性及其影响因素

乳铁素B是牛乳铁蛋白经胃蛋白酶酶解后得到的最重要的抗菌肽,具有较强抗菌活性．研究表明,乳铁素B对大肠杆菌的最小抑菌质量浓度为0．5mg／mL,对金黄色葡萄球菌的最小抑菌浓度为0．4mg／mL;葡萄糖、蔗糖、麦芽糖、牛血清白蛋白(BSA)、尿素、硫酸铵在0～10mg／mL,乳糖、可溶性淀粉在0～4mg／mL,的质量浓度范围内,对乳铁素B的抗菌活性影响不大;当NaCl或KCl的浓度为25～100mmol／L,MgCl2或CaCl2的浓度为1．0～5．0mmol／L时,乳铁素B的抗菌活性就会大大降低;随着缓冲盐浓度和有机酸浓度(25～100mmol／L)的增大,乳铁素B的抗菌活性呈下降趋势,且在微碱性环境下乳铁素B表现出较强的抗菌活力．     

天然及合成甜味剂的最新进展

<正> 甜味剂的使用可以追溯到史前时期蜂蜜的发现。科学研究已经表明,人类对甜味的需求是先天的,而不是后天对环境要求的一种客观反应。 甜味剂发展概况 五、六十年代以前的近一个世纪,糖精是人们所能应用的唯一的高甜度甜味剂。五、六十年代之后,甜蜜素、二肽甜味剂以及Acesulfamek等在美国、欧洲及日本等国相继     

牛乳铁蛋白及乳铁素的生产与应用现状

牛奶中的乳铁蛋白和其水解产物乳铁素具有多种生物活性功能。综述了国外的乳铁蛋白和乳铁素生产、分离和纯化的方法,并介绍了乳铁蛋白和乳铁素作为食品保存剂、抗氧化剂、营养强化剂、免疫强化剂、免疫调节剂等应用的现状。展望了我国乳铁蛋白和乳铁素生产的前景。     

pH值对新型广谱细菌素Garviecin LG34抗菌活性及结构的影响

文章研究了pH值对新型广谱乳酸菌细菌素Garviecin LG34抗菌活性和结构的影响,并在此基础上研究细菌素结构与抗菌活性之间的关系。结果表明酸性(pH≤5)和碱性(pH≥8)环境使细菌素Garviecin LG34抗菌活性显著下降(P<0.05)。拉曼光谱分析结果表明细菌素Garviecin LG34的二级结构主要由α-螺旋结构和无规则卷曲结构组成。pH值范围在4.0～6.0,随着pH值的下降α-螺旋结构占比显著下降(P<0.05);pH值范围在7.0～9.0,随着pH值的升高α-螺旋结构占比显著下降(P<0.05)。因此pH值显著影响α-螺旋结构占比和抗菌活性,而且α-螺旋结构占比与细菌素Garviecin LG34抗菌活性之间具有正相关性。     

乳铁蛋白活性多肽的抑菌性能

概述了乳铁蛋白活性多肽的结构、制备方法、抑菌谱、抑菌机理及抑菌活性的影响因素.     

Mammary gland expression of antibacterial peptide genes to inhibit bacterial pathogens causing mastitis

As a step toward prevention of bovine mastitis, a plasmid-mediated gene transfer technique was used to enable mammary cells to synthesize and secrete bovine lactoferricin and bovine tracheal antibacterial peptides. For this purpose, a series of mammary tissue-specific expression vectors, harboring the antibacterial peptide gene, the 5′-flanking regulation sequence of goat β-casein, and the bovine growth hormone polyadenylation signal sequence, were constructed using a eukaryotic expression vector pIRES1-neo. The mammary gland tissue-specific expression vector carrying the antimicrobial peptide genes dissolved in physiologic saline was injected directly into the lactating mammary glands of goats. The milk samples after injection were checked by Tricine-SDS-PAGE and bacterium inhibition zone assay. The results of these tests showed that the mammary gland tissue-specific expression vector driven by the goat β-casein gene promoter could efficiently direct the expression of antibacterial peptides in goat milk; the expression of antibacterial proteins lasted for 3 to 6 d. All of the milk samples collected from the mammary glands that had been injected with different vectors harboring the antibacterial peptide gene(s) exhibited bacteriostatic activity against different bacterial pathogens. These results demonstrated that the mammary gland tissue-specific expression vector could be used to introduce antibacterial peptide gene into the goat mammary gland, enabling secretion of a bioactive form of antibacterial peptide in the milk. This successful expression of antibacterial peptides in goat mammary glands provided a possible method to prevent mastitis in ruminants.     

酪蛋白来源新型抗菌肽(Trpi)抗菌活性的初步研究

本实验对本实验室最近通过胰蛋白酶水解酪蛋白纯化得到了一种新的具有抗菌活性的多肽(Trpi)进行了初步的抗菌试验,实验测定了该肽的抑菌效果,结果表明该肽可抑制多种细菌的生长,尤其是对大肠杆菌和金黄色葡萄球菌具有很强的抗菌作用,显示出该抗菌肽具有非常大的科研和应用价值。     

鲁西黄牛乳铁蛋白N-末端多肽基因的表达与活性检测

从黄牛的肝脏中提取总的DNA，根Genebank牛乳铁蛋白的cDNA序列，设计特异性引物，采用RT-PCR进行扩增，将扩增片段克隆于PGEM－Teasy　vector中。测序结果表明，该片断是乳铁蛋白基因的cDNA序列，编码50个氨基酸的150bp的多肽片断，通过BamH1和ＥcoR1双酶酶切该片断，并连接到表达载体PGEX-4T1中，转化大肠杆菌BL21，进行诱导表达，蛋白电泳显示，表达成功；经纯化、胃蛋白酶酶解后，具有抗菌生物活性。     

Identification of milk proteins enhancing the antimicrobial activity of lactoferrin and lactoferricin

Lactoferrin (LF) is known as an iron-binding antimicrobial protein present in exocrine secretions such as milk and releases the potent antimicrobial peptide lactoferricin (LFcin) by hydrolysis with pepsin. The antimicrobial activity of LF and LFcin has been studied well; however, their cooperative action with other milk proteins remains to be elucidated. In this study, we identified milk proteins enhancing the antimicrobial activity of bovine LF and LFcin against gram-negative bacteria, gram-positive bacteria, and fungi. As the target fraction, we isolated a minor milk protein fraction around 15 kDa, which was identified as bovine RNase 5 (angiogenin-1), RNase 4, and angiogenin-2 by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. As these proteins are collectively known as the RNase A family, we referred to the target protein fraction as milk RNase of 15 kDa (MR15). The number of colony-forming units of Escherichia coli and other pathogenic microorganisms with the addition of MR15 to LF (MR15:LF ratio = 16:1,000) was dramatically lowered than that with LF alone. On the other hand, MR15 itself did not show any reductions in the number of colony-forming units at the concentrations tested. Similarly, the antimicrobial activities of LFcin against various microorganisms were significantly enhanced by the addition of MR15. These results suggest that LF and MR15 may be concomitantly acting antimicrobial agents in milk.     

Bovine lactoferricin B induces apoptosis of human gastric cancer cell line AGS by inhibition of autophagy at a late stage

Gastric cancer is one of the most common malignant cancers, with poor prognosis and high mortality rates worldwide. Therefore, development of an effective therapeutic method without side effects is an urgent need. It has been reported that cationic antimicrobial peptides can selectively bind to negatively charged prokaryotic and cancer cell membranes and exert cytotoxicity without causing severe drug resistance. In the current study, we prepared a series of peptide fragments derived from bovine lactoferrin and evaluated their anticancer potency toward the gastric cancer cell line AGS. Cell viability assay revealed that a 25-AA peptide fragment, lactoferricin B25 (LFcinB25), exhibited the most potent anticancer capability against AGS cells. Lactoferricin B25 selectively inhibited AGS cell growth in a dose-dependent manner, exhibiting a half-maximal inhibitory concentration (IC₅₀) value of 64 μM. Flow cytometry showed a notable increment of the sub-G₁ populations of the cell cycle, indicating the induction of apoptosis by LFcinB25. Western blot analysis further revealed that upon LFcinB25 treatment for 2 to 6 h, apoptosis-related caspases-3, 7, 8, 9, and poly(ADP-ribose) polymerase (PARP) were cleaved and activated, whereas autophagy-related LC3-II and beclin-1 were concomitantly increased. Thus, both apoptosis and autophagy are involved in the early stage of LFcinB25-induced cell death of AGS cells. However, upon treatment with LFcinB25 for 12 to 24 h, LC3-II began to decrease, whereas cleaved beclin-1 increased in a time-dependent manner, suggesting that consecutive activation of caspases cleaved beclin-1 to inhibit autophagy, thus enhancing apoptosis at the final stage. These findings provide support for future application of LFcinB25 as a potential therapeutic agent for gastric cancer.     

天山花楸叶抗菌作用研究

用一系列细菌和真菌试验了天山花楸叶乙醇提取物的抑菌作用。结果表明一定浓度的天山花楸叶乙醇提取物对供试细菌和真菌都显示出一定的抑制作用,MIC和MBC均较低,其抑菌活性随着提取物浓度的增大而逐渐增强。提取物对高温、紫外线都具有良好的稳定性。因此天山花楸叶乙醇提取物可用于食物防腐、保鲜等领域,具有广泛的使用范围。