关于氨基酸等电点计算的讨论

氨基酸作为蛋白质的基本组成单位，成为蛋白质化学中不可缺少的重要内容。氨基酸是一种两性化合物，随溶液的ｐＨ值不同，可能出现三种状态：带正电荷，带负电荷，净电荷为零。根据氨基酸的这三种不同状态，采用５种方法计算氨基酸的等电点。     

肌酸激酶多聚电解质特性研究

本文从理论上导出了蛋白质的净电荷、正电荷、负电荷随ｐＨ值的变化关系式，应用于氨基酸和多肽的计算。结果与实验完全一致。用荧光偏振和荧光光谱对肌酶激酶带电性随ｐＨ珠变化关系的研究表明，理论计算符合实验结果，这表明本文的理论关系式处理蛋白质的带电荷数是可靠的，同时，根据模型合理地解释了蛋白酶抗碱性能力比抗酸性能力强的现象。     

中南地区几种土壤的表面电荷特性

在比较几种测定土壤电荷零点方法的基础上,研究了中南地区几种土壤的正负电荷量、电荷零点（ＰＺＧ）和净电荷零点（ＰＺＮＣ）。（１）推荐将盐滴定－电位滴 作为测定土壤ＰＺＣ的常规方法,该法较电位测定（ＰＴ）法简便、消耗样品量较少,而比盐滴定（ＳＴ）法获取的信息量较多。（２）铁铝氧化物是土壤正电荷的主要载体,其中非晶形铁铝氧化物具有重要贡献。（３）在低ＰＨ时土壤主要带永久负电荷随ＰＨ升高,土壤可变负电荷量     

硝基肥适合旱田作物

<正>旱田:硝基肥利用率高硝基肥中的氮由铵态氮和硝态氮组成。铵态氮带正电荷,能够被带负电荷的土壤颗粒所吸附,肥效期较长,但在撒施在地表的情况下易变成氨气挥发;硝态氮在旱田中非常稳定,不易挥发和流失,同时硝态氮的溶解性非常好,移动性非常好,在旱田中的吸收利用率非常高,但在水田淹水条件下,易反硝化成氧化氮挥发     

新审杂交水稻品种耐热性评价

在定量高温和自然常温条件下以耐热性品种N22为对照,研究了近年审定的适应四川生态区种植的35个杂交稻的耐热性.筛选出耐热品种9个,并通过耐热指数将35个杂交水稻品种分为耐热能力不同的4类,可为水稻生产布局提供科学依据.     

罐顶附件对接法兰设置跨接线的必要性

一、雷击的二次放电原理 当雷云在空中缓慢移动时,处在云团下方大面积的地表面将形成一个静电场,电场在地面、油罐以及其它物体表面感应产生相反的电荷,并随云团移动。图1是带负电荷的雷云靠近一拱顶油罐的情形。雷云在整个拱顶及其附件上感应产生正电荷,各部件正电荷的密度与各部件的形状、材质、离云团的距离等因素有关,突出部位感应的正电荷密度较大,例如,避雷针尖端的正电荷密度大于安全阀、呼吸阀及     

减少鸡粪污染两措施

1.合理的饲料配制①选用高质量的原料.尽量选用高质量的蛋白质饲料和生物学利用率高的磷源,使氨基酸的平衡情况符合"理想蛋白质"的氨基酸构成,提高蛋白质的消化利用率,提高磷的利用率,减少氮、磷的排出量,从而减轻鸡粪对环境的污染.     

减少鸡粪污染两措施

1合理的饲料配制1.1选用高质量的原料。尽量选用高质量的蛋白质饲料和生物学利用率高的磷源,使氨基酸的平衡情况符合“理想蛋白质”的氨基酸构成,提高蛋白质的消化利用率,提高磷的利用率,减少氮、磷的排出量。1.2合理配制日粮,精心平衡日粮中的各项营养成分,使其符合鸡的需要量     

安徽沿淮地区几种类型土壤表面电荷特征

用Mechlich法研究沿淮地区几种类型土壤的电荷数量,结果表明：不同类型土壤电荷数量、电荷性质存在明显差异。供试土壤负电荷量大于土壤正电荷量,土壤永久负电荷量大于可变负电荷量。在沿淮几种土壤中,黄棕壤、黄褐土CECv／CEC8．2≥0．4,为可变电荷土壤,潮土和砂姜黑土为恒电荷土壤。土壤性质是土壤表面电荷的主要影响因素,CECv和CEC8．2主要受土壤pH和粘粒含量的影响,AEC主要受土壤有机质的影响。     

番木瓜种子盐溶蛋白的氨基酸分析

采用 CM-纤维素柱层析方法提取、分析了番木瓜种子盐溶蛋白的各组分,用聚丙烯酰胺凝胶电泳的酸、碱性系统测定了蛋白质的电荷性质以及用 SDS-PAGE 测定了各蛋白质的分子量,并分析测试了各蛋白组分的氨基酸含量。表明:番木瓜种子盐溶蛋白只有在酸性系统才能得到分离,蛋白性质均为带正电荷的碱性蛋白,其分子量为11000～49000。各蛋白组分氨基酸以谷氨酸及酰胺、精氨酸为最多,其他必需氨基酸含量不平衡。其中低分子量蛋白中的含硫氨基酸较高,这种蛋白可以起还原胰岛素和调节木瓜蛋白酶活性的作用。     

Structure of the GDP domain of EF-Tu and location of the amino acids homologous to ras oncogene proteins

A 2.7 angstrom resolution x-ray diffraction analysis of a trypsin-modified form of the Escherichia coli elongation factor Tu reveals that the GDP-binding domain has a structure similar to that of other nucleotide-binding proteins. The GDP ligand is located at the COOH-terminal end of the beta sheet and is linked to the protein via a Mg2+ ion salt bridge. The location of the guanine ring is unusual; the purine ring is located on the outer edge of the domain, not deep within a hydrophobic pocket. The amino acids from Pro10 to Arg44 and from Gly59 to Glu190 have been assigned to the electron density with computer graphic techniques, and the resulting model is consistent with all known biochemical data. An analysis of the structure reveals that four regions of the amino acid sequence that are homologous with the family of ras oncogene proteins, termed p21, are located in the vicinity of the GDP-binding site, and most of the invariant amino acids shared by the proteins interact directly with the GDP ligand.     

Effects of buried ionizable amino acids on the reduction potential of recombinant myoglobin

The temperature dependences of the reduction potentials (E degrees') of wild-type human myoglobin (Mb) and three site-directed mutants have been measured by the use of thin-layer spectroelectrochemistry. Residue Val68, which is in van der Waals contact with the heme in Mb, has been replaced by Glu, Asp, and Asn. The changes in E degrees' and the standard entropy (delta S degrees') and enthalpy (delta H degrees') of reduction in the mutant proteins were determined relative to values for wild type; the change in E degrees' at 25 degrees C was about -200 millivolts for the Glu and Asp mutants, and about -80 millivolts for the Asn mutant. At pH 7.0, reduction of Fe(III) to Fe(II) in the Glu and Asp mutants is accompanied by uptake of a proton by the protein. These studies demonstrate that Mb can tolerate substitution of a buried hydrophobic group by potentially charged and polar residues and that such amino acid replacements can lead to substantial changes in the redox thermodynamics of the protein.     

成熟中国鲎卵的营养成分分析

分别采用凯氏定氮法、索氏脂肪抽提称量法、反相液相色谱法及和相色谱-质谱法测定了成熟中国鲎卵中粗蛋白、粗脂肪、氨基酸及脂肪酸的含量。结果表明,中国鲎卵粗蛋白和粗脂肪含量分别为61.90%和15.82%;鲎卵至少含有16种氨基酸,其中异亮氨酸(Ile)、酪氨酸(Tyr)、亮氨酸(Leu)、赖氨酸(Lys)和天冬氨酸(Asp)含量较高,占氨基酸总量的60%以上;鲎卵至少含18种脂肪酸,其中不饱和脂肪酸(UFA)有7种,高度不饱和脂肪酸(HUFA)4种,分别占总游离脂肪酸含量的60.71%和13.15%。     

Protein catalysis of the retinal subpicosecond photoisomerization in the primary process of bacteriorhodopsin photosynthesis

The rate of retinal photoisomerization in wild-type bacteriorhodopsin (wt bR) is compared with that in a number of mutants in which a positively charged (Arg(82)), a negatively charged (Asp(85) or Asp(212)), or neutral hydrogen bonding (Asp(115) or Tyr(185)) amino acid residue known to be functionally important within the retinal cavity is replaced by a neutral, non-hydrogen bonding one. Only the replacements of the charged residues reduced the photoisomerization rate of the 13-cis and all-trans isomers present in these mutants by factors of approximately 1/4 and approximately 1/20, respectively. Retinal photo- and thermal isomerization catalysis and selectivity in wt bR by charged residues is discussed in terms of the known protein structure, the valence-bond wave functions of the ground and excited state of the retinal, and the electrostatic stabilization interactions within the retinal cavity.     

新疆迪西型鹰嘴豆中脂肪和蛋白质组分的研究（摘要）

[目的]提取新疆产地的迪西型鹰嘴豆的油脂,测定脂肪酸含量及组份,并测定迪西型鹰嘴豆的分级蛋白和蛋白质氨基酸组成。[方法]以新疆产地的迪西型鹰嘴豆为试验材料,提取其种仁油脂。用气相色谱-质谱法测定脂肪酸的含量及组分;采用微量定氮法和分级提取法测定粗蛋白和分离蛋白,并对蛋白质中的氨基酸组成进行了分析。[结果]鹰嘴豆中油脂含量高（为18.2%）,油脂以不饱和脂肪酸油酸、亚油酸为主要成分,占脂肪酸总量80%以上,饱和脂肪酸含量较低。鹰嘴豆中粗蛋白质含量平均为23.71%,以球蛋白和清蛋白为主,占蛋白质总量的80%以上,而谷蛋白、醇溶蛋白含量比较低。其蛋白质均含18种氨酸酸,属完全蛋白质。谷氨酸含量最高,占蛋白质的15.8%。天冬氨酸含量占10.7%。此外还有精氨酸（9.30%）、亮氨酸（7.56%）和赖氨酸（6.34%）,其次为苯丙氨酸、丙氨酸、缬氨酸、异亮氨酸。色氮酸、蛋氨酸和胱氨酸含量最少。鹰嘴豆中必需氨基酸含量丰富。[结论]新疆迪西型鹰嘴豆是一种不饱和脂肪酸含量很高,氨基酸含量丰富的豆类作物。     

源于银杏叶片中一个抗真菌蛋白（GAFP—1）的分离、纯化和鉴定

经过 8 0 %饱和度硫酸铵沉淀、几丁质亲和层析和SephadexG 75的凝胶过滤层析 3个步骤 ,从银杏(GinkgoBilobaL )的叶片中纯化获得 1个抗真菌蛋白 ,把它命名为GAFP 1。以SDS PAGE胶为基础进行电泳分析 ,GAFP 1的分子量约为 30kD。氨基酸组分分析显示 ,1mlGAFP 1的甘氨酸、谷氨酸和天冬氨酸残基较其它氨基酸残基多。抑菌分析表明 :1μg或 2 μg的GAFP 1能够抑制水稻纹枯病菌和棉花炭疽病菌菌丝的生长 ,但对水稻稻瘟病菌和小麦纹枯病菌菌丝的生长没有抑制效果。GAFP 1的N 端 10个氨基酸残基为Asp Pro Gly Cys Asn Val Leu Glu Asp Ile ,以这 10个氨基酸残基为基础进行同源性比较发现 ,它与蛋白质数据库中已知的蛋白质没有同源性 ,表明GAFP 1可能是 1个新的抗真菌蛋白     

叶面喷施天然海盐和尿素对苦瓜品质的影

在苦瓜苗期喷施天然海盐和尿素,成熟期检测苦瓜的比叶面积、矿质元素、叶绿素、氨基酸、维生素Ｃ的含量和抗氧化活性等生理指标,以探明叶面喷施天然海盐和尿素对苦瓜食品价值的影响。结果表明：叶面喷施尿素,降低了苦瓜的光合效率,提高了矿质元素 Ｍｇ,Ｓｉ,Ｐ,Ｋ和各种氨基酸的含量,特别是苦瓜体内的叶绿素 ａ和 ｂ的含量。喷施海盐显著地提高了苦瓜叶片的光合效率,促进了对 Ｍｇ,Ｓｉ,Ｐ,Ｓ,Ｋ的吸收,增加了叶绿素 ａ,ｂ的含量 （增量低于尿素处理）,增加了天冬氨酸、缬氨酸、亮氨酸、酪氨酸、苯丙氨酸、赖氨酸、组氨酸和精氨酸的含量,提高了维生素 Ｃ的含量和抗氧化活性。尿素和海盐组合处理显著提高了苦瓜对 Ｋ的吸收,提高了天冬氨酸的含量,但其它氨基酸的含量并没有尿素处理的高。综上所述,叶面喷施天然海盐和尿素改善了苦瓜的某些品质。由于海盐和尿素单独使用的局限性,因此合理分配海盐和尿素的比例或适当补充某些矿质元素进行叶片处理,可能更有利于苦瓜的品质。     

通过蛋白质序列比对探讨细菌的热适应机制

[目的]从蛋白的一级序列特征出发探索原核生物的热适应机制。[方法]从526种原核生物的蛋白序列中识别出同源蛋白,并对其进行了综合分析。[结果]找到了存在于超嗜热、嗜热细菌的同源蛋白组（HT-only）95种和仅存在于常温细菌中的同源蛋白组（M-only）1659种,发现了氨基酸组成与细菌最适生长温度存在显著的相关性。结合在超嗜热、嗜热、常温和嗜冷细菌中都有分布的同源蛋白组（Top-90）,通过分析得出HT-only和Top-90组的同源蛋白簇非常相似,而M-only组与其他2组有所不同。[结论]从原核生物全蛋白序列的角度,证实了氨基酸组成与热稳定性存在的显著相关性,验证了先前学者的关于蛋白氨基酸组成与嗜热机制相关性的研究结论。     

A general method for site-specific incorporation of unnatural amino acids into proteins

A new method has been developed that makes it possible to site-specifically incorporate unnatural amino acids into proteins. Synthetic amino acids were incorporated into the enzyme beta-lactamase by the use of a chemically acylated suppressor transfer RNA that inserted the amino acid in response to a stop codon substituted for the codon encoding residue of interest. Peptide mapping localized the inserted amino acid to a single peptide, and enough enzyme could be generated for purification to homogeneity. The catalytic properties of several mutants at the conserved Phe66 were characterized. The ability to selectively replace amino acids in a protein with a wide variety of structural and electronic variants should provide a more detailed understanding of protein structure and function.     

Bacterial rhodopsin: evidence for a new type of phototrophy in the sea

Extremely halophilic archaea contain retinal-binding integral membrane proteins called bacteriorhodopsins that function as light-driven proton pumps. So far, bacteriorhodopsins capable of generating a chemiosmotic membrane potential in response to light have been demonstrated only in halophilic archaea. We describe here a type of rhodopsin derived from bacteria that was discovered through genomic analyses of naturally occuring marine bacterioplankton. The bacterial rhodopsin was encoded in the genome of an uncultivated gamma-proteobacterium and shared highest amino acid sequence similarity with archaeal rhodopsins. The protein was functionally expressed in Escherichia coli and bound retinal to form an active, light-driven proton pump. The new rhodopsin exhibited a photochemical reaction cycle with intermediates and kinetics characteristic of archaeal proton-pumping rhodopsins. Our results demonstrate that archaeal-like rhodopsins are broadly distributed among different taxa, including members of the domain Bacteria. Our data also indicate that a previously unsuspected mode of bacterially mediated light-driven energy generation may commonly occur in oceanic surface waters worldwide.