Mechanism of intramolecular mixed anhydride formation as intermediates in the reactions of N-phosphorylamino-acids──An MNDO research

N-phosphoryl-α-amino acids can react to form esters, peptides, phosphoryl ester-exchanged products and phosphoryl group migration products under mild conditions, which are very important in researches on arohebiont. It has been proposed that intramolecular mixed carboxylic-phosphoric anhydrides (IMCPAs) might be the common intermediates of the reactions, which are difficult to be experimentally observed because of their high activity. In this note, it has been revealed, by means of MNDO, that the IMCPAs are situated at the relatively minimal points of the potential surface and can form in a non-synchronous concerted reaction pathway that passes through a transition state with a hydrogen-bond-bridge structure. The results give a successful explanation to the structure and formation of IMCPAs and their ability to promote the various reactions mentioned above.     

Pancreastatin, a novel pancreatic peptide that inhibits insulin secretion

In mammalian tissues the C-terminal amide structure has been found to occur only in neuroactive or hormonally-active peptides. About half known neuropeptide and peptide hormones have this unique chemical feature. Using a chemical detection method, a search for previously unknown peptides that possess the C-terminal amide structure in extracts of brain and intestine was carried out and a number of novel neuropeptides and hormonal peptides, designated neuropeptide Y, PHI, peptide YY, galanin and neuropeptide K were isolated. We recently performed a similar search in porcine pancreas and found a high concentration of a peptide having a glycine amide at its C-terminus. Here we report the isolation, primary structure and biological activity of this novel peptide. The 49-residue peptide strongly inhibits glucose-induced insulin release from the isolated perfused pancreas and was therefore named pancreastatin. It may be important in the regulation of insulin secretion and in the pathogenesis and treatment of diabetes mellitus.     

Hydrogen Peroxide in Fluorinated Alcohols：A Potent and Selective Oxidative System

1 Introduction Fluorinated alcohols such as 1,1,1,3,3,3-hexafluoro-2-propanol and 2,2,2-trifluoroetanol have particular properties compared to non-fluorinated ones and could provoke changes in the course of reactions in these solvents. Their specific properties are connected mainly to the strong hydrogen bond donor ability and solvation of nuclephiles on one side, and weak hydrogen bond acceptor strength and weak solvation of electrophiles on the other. This dichotomy makes them very attractiv…     

Isolation of two novel candidate hormones using a chemical method for finding naturally occurring polypeptides

Naturally occurring peptides with biological actions have in most cases been detected by observing their biological activities in crude extracts and their isolation has been followed using bioassays. As a complement to the classical biological detection systems, we have proposed a chemical detection system based on fragmentation of peptides in tissue extracts followed by identification of certain of these peptide fragments having distinct chemical features. One such chemical feature is the C-terminal amide structure which is characteristic of many biologically active peptides. We have devised a chemical assay method for peptides having such a structure and have found several previously unknown peptide amides in procine upper small intestinal tissues. We report here the isolation and characterization of two of them, designated PHI and PYY. PHI is related to secretin, vasoactive intestinal polypeptide (VIP, glucagon and gastric inhibitory polypeptide (GIP); PYY is related to the pancreatic polypeptide and to neurotensin. Both peptides exhibit biological activities and appear to be present not only in the intestine but also in brain.     

A transglutaminase homologue as a condensation catalyst in antibiotic assembly lines

The unrelenting emergence of antibiotic-resistant bacterial pathogens demands the investigation of antibiotics with new modes of action. The pseudopeptide antibiotic andrimid is a nanomolar inhibitor of the bacterial acetyl-CoA carboxylase that catalyses the first committed step in prokaryotic fatty acid biosynthesis. Recently, the andrimid (adm) biosynthetic gene cluster was isolated and heterologously expressed in Escherichia coli. This establishes a heterologous biological host in which to rapidly probe features of andrimid formation and to use biosynthetic engineering to make unnatural variants of this important and promising new class of antibiotics. Bioinformatic analysis of the adm cluster revealed a dissociated biosynthetic assembly system lacking canonical amide synthases between the first three carrier protein domains. Here we report that AdmF, a transglutaminase (TGase) homologue, catalyses the formation of the first amide bond, an N-acyl-beta-peptide link, in andrimid biosynthesis. Hence, AdmF is a newly discovered biosynthetic enzyme that acts as a stand-alone amide synthase between protein-bound, thiotemplated substrates in an antibiotic enzymatic assembly line. TGases (enzyme class (EC) 2.3.2.13) normally catalyse the cross-linking of (poly)peptides by creating isopeptidic bonds between the gamma-carboxamide group of a glutamine side chain of one protein and various amine donors, including lysine side chains. To the best of our knowledge, the present study constitutes the first report of a TGase-like enzyme recruited for the assembly of an antibiotic. Moreover, genome mining using the AdmF sequence yielded additional TGases in unassigned natural product biosynthetic pathways. With many more microbial genomes being sequenced, such a strategy could potentially unearth biosynthetic pathways producing new classes of antibiotics.     

Novel C-terminally amidated opioid peptide in human phaeochromocytoma tumour

As has often been observed in hypothalamic releasing factors and gastrointestinal hormones, the carboxy-terminal amide structure is a unique feature of peptides exhibiting hormonal or physiological activities. Although a variety of opioid peptides have hitherto been identified, such a C-terminal amidated species has never before been discovered in mammals. Here we present the first identification of a novel opioid octapeptide with a C-terminal amide structure, henceforth designated as 'adrenorphin', in human phaeochromocytoma tumour derived from adrenal medulla. The complete amino acid sequence of adrenorphin was determined by microsequencing and corresponds to the sequence of the first eight amino acids of peptide E which is derived from proenkephalin A. Adrenorphin has also been identified chromatographically in normal human and bovine adrenal medulla. Adrenorphin exhibits potent opioid activity in guinea pig ileum assay, suggesting a specialized physiological function.     

A kinetic intermediate in the reaction of an antigenic peptide and I-Ek

Helper T cells are triggered by molecular complexes of antigenic peptides and cell surface glycoproteins of the MHC (gene products of the major histocompatibility complex) on antigen-presenting cells. There is now a lot of evidence that the complexes between isolated class II MHC molecules and selected peptides have long half-lives of approximately one day. The reported equilibrium binding constants between antigenic peptides and class II MHC molecules however, are only micromolar, suggesting that the association rate constants are very low. The only reported association rate constant is for a chicken ovalbumin peptide (OVA323-339) binding to I-Ad, and is indeed remarkably low, about 1 litre per mole per second. Prompted by these unusual data, we have used the pigeon cytochrome-c peptide pCytc(88-104) and I-E reconstituted in planar lipid bilayers on glass slides to investigate further the kinetics of peptide-MHC reactions. We report the formation of two IEk-pCytc peptide complexes. One complex has slow apparent association and dissociation kinetics, very similar to those reported previously for the chicken ovalbumin peptide and I-Ad. The second complex forms and dissociates about a hundred times more rapidly. The short-lived complex shows peptide-MHC specificity and is a kinetic intermediate in the formation of the long-lived complex; the long-lived complex is recognized by specific T-helper cells.     

钯/硫酰胺配体催化下Csp~2-Csp~2交叉偶联反应

Pd(CH3CN)2Cl2与硫酰胺配体形成的金属络合物为催化剂应用到Csp2-Csp2成键的Negishi(根岸英一)偶联反应中去,发现此催化体系不但反应速度很快,并且催化剂的量比例比较小,这说明反应效率比较高.当使用苯基锌试剂与对碘苯甲酸乙酯的反应时,发现催化体系TON值可以达到105,并且代物催化体系对溴化物的兼容性相对较好,在室温下就能对溴代物和碘代物很好的分离.在通过筛选条件之后,发现对溴的选择性可以达到90%以上.并且,对氯代物的兼容性研究发现,采用同样的方法可以达到97%以上.     

海水中氨基酸对Cu(Ⅱ)-粘土粒子相互作用的影响

对天然海水中氨基酸－ 金属铜离子Ｃｕ（Ⅱ）－ 粘土三元体系中三元表面配合物形成及影响因素进行了研究⒀采用交换吸附百分率ＥＣｕ（Ⅱ）～ｐＨ关系曲线法研究表明,一定浓度范围内氨基酸对铜离子Ｃｕ（Ⅱ）在高岭石上的交换吸附百分率ＥＣｕ（Ⅱ）～ｐＨ关系曲线（Ｓ型曲线） 的影响有“左右摆动”规律, 认为体系中形成了三元表面配合物 ＳＯＨＬＭ （新型（Ⅱ）类）; 实验比较了三种氨基酸的影响⒀三元表面配合物的形成主要受固体粒子表面结构、氨基酸存在形式以及它们的络合能力等的影响     

PA6/69熔融共混体系酰胺交换反应动力学模型——Monte Carlo模拟

建立了酰胺交换反应动力学 Monte Carlo的基本模型,并用该模型对 PA6/69熔融共混体系中4种酰胺键摩尔分数随时间的变化进行了模拟.模拟结果表明,PA6/69嵌段共聚物在283℃下的寿命为8h,这与Nllen的研究结果相吻合.     

Beta 2-microglobulin restriction of antigen presentation.

Antigens are generally thought to be recognized by cytotoxic T lymphocytes as peptides in the context of class I major histocompatibility proteins complex, which are heterodimers of heavy chains noncovalently associated with beta 2-microglobulin (beta 2m). The highly polymorphic nature of the heavy chains and their resulting ability to present different sets of peptides has presumably evolved to allow potent immune responses against most pathogens. By contrast, the polymorphism of beta 2m is limited; seven alleles are known in the mouse and only one has been identified in humans. beta 2-Microglobulin was consequently thought to have only structural functions: namely, to ensure correct folding of class I molecules and their transport to the cell surface. Although beta 2m is not implicated directly in the formation of the peptide binding site, we report here that it participates in the selection of MHC class I molecule-associated peptides.     

Synthesis and structural analysis of 2-quinuclidonium tetrafluoroborate

The amide functional group is one of the most fundamental motifs found in chemistry and biology, and it has been studied extensively for the past century. Typical acyclic amides are planar. But the amide groups of bicyclic bridgehead lactams are highly twisted, and this distortion from planarity can dramatically affect the stability and reactivity of these amides; it also increases the basicity of the nitrogen so that it often behaves more like an amine than a typical planar amide. As a result, the structures and reactivity profiles of these 'anti-Bredt' amides differ significantly from those of planar amides. It is possible that this twisting phenomenon is not exclusive to cyclic systems-non-planarity may also be a critical biological design element that leads to amide ground-state destabilization and alters the reactivity, selectivity and mechanism of various protein and enzymatic processes (such as amide hydrolysis). The intriguing qualities of these twisted amides were first recognized in 1938 (ref. 11), wherein one of the simplest families was introduced--molecules containing the 1-azabicyclo[2.2.2]octan-2-one system. But the parent member of this group, 2-quinuclidone (molecule 1 in this paper), has not yet been unambiguously synthesized. Here, we report the chemical synthesis, isolation and full characterization of the HBF4 salt of 1. Critical to the success of the synthesis and isolation was the decision to generate 1 by a route other than classical amide bond formation. We anticipate that these results will provide a greater understanding of the properties of amide bonds.     

小肽不同高效液相色谱柱前衍生化反应的实验研究

分别用氯甲酸-9-芴基甲酯(9-fluorenylmethylchloroformate,FMOC-Cl)、9-芴基甲氧基甲酸琥珀酰亚胺类酯(9-fluorenylmethoxy carbonyl succinimide,FMOC-OSU)和丹磺酰氯(1-dimethylaminonaphthalene-5-sulfonyl-chloride,Dns-Cl)为衍生化试剂对小肽进行了衍生化反应.研究和比较了各种衍生试剂用量、衍生缓冲体系pH条件、衍生化时间等因素对衍生反应的影响及衍生产物的稳定性.结果发现,FMOC-Cl对肽的衍生反应速度快,衍生反应完全,衍生产物稳定.     

Isolation and structure of a novel C-terminally amidated opioid peptide, amidorphin, from bovine adrenal medulla

Biologically active peptide hormones and neurotransmitters have been shown to be enzymatically liberated from larger, inactive precursor molecules by tissue-specific post-translational processing, particularly at the typical cleavage signals of paired basic residues. Subsequent N-terminal or C-terminal modifications may be of importance in regulating the biological activities of these peptides. C-terminal alpha-amidation is considered to be essential for the biological function of several non-opioid peptides. Here we present the isolation and structure of a novel C-terminally amidated opioid peptide, amidorphin, from bovine adrenal medulla. Amidorphin and the recently isolated octapeptide metorphamide (adrenorphin) are the only endogenous opioid peptides in mammals known to possess a C-terminal amide group. The amino acid sequence of amidorphin corresponds to the sequence 104-129 of bovine proenkephalin A. Very high concentrations of amidorphin were detected in bovine adrenal medulla and in a further endocrinological system, the hypothalamic-neurohypophyseal axis. Amidorphin may therefore be considered to be a major gene product of the opioid peptide precursor proenkephalin A in these endocrine tissues.     

氧方酸与一些酰胺的反应研究

氧方酸与磷酰胺ＨＭＰＡ、羧酰胺的可能的反应历程。氧方酸酸解二甲基甲酰胺和二甲基乙酰胺的反应是分步进行的。氧方酸与其它物质在ＤＭＦ中反应时，不能忽略ＤＭＦ的参与作用。氧方酸与ＨＭＰＡ反应是制备１，３－双－Ｎ，Ｎ－二甲基异方酰胺的好方法，与氨基甲酸乙酯或乙酰胺的反应可用于氮氧方酸（３－氨基－４－羟基－３－环丁烯二酮）的制备。     

Short alanine-based peptides may form 3(10)-helices and not alpha-helices in aqueous solution.

Short alanine peptides, containing 16 or 17 residues, appear to form alpha-helices in aqueous solution. But the main spectroscopic analyses used on helical peptides (circular dichroism and nuclear magnetic resonance) cannot distinguish between an alpha-helix (in which the ith residue is hydrogen-bonded to residue i + 4; ref. 9) and the next most common peptide helix, the 3(10)-helix10 (i-->i + 3 hydrogen-bonding). To address this problem we have designed single and doubly spin-labelled analogues of alanine-based peptides in which the nitroxide spin label forms an unbranched side chain extending from the sulphur atom of a cysteine residue. Here we report the circular dichroism, Fourier-transform infrared and electron-spin resonance spectra of these peptides under helix-forming conditions. The infrared absorbance gives an amide I' band with a frequency that is substantially different from that observed for alpha-helices. The electron-spin resonance spectra of doubly labelled helices show that the ranking of distances between side chains, around a single turn (residues 4-8), is inconsistent with an alpha-helical structure. Our experiments suggest that the more likely peptide geometry is a 3(10)-helix.     

植物过氧化物酶的结构、催化反应及生理功能

过氧化物酶(EC.1.11.1.7)是一种以H_2O_2作为电子受体催化底物的氧化作用的酶,这种酶广泛存在于生物体中,这种酶已被广泛研究。本文讨论了过氧化物酶的化学结构、过氧化物酶的亚基构成、它们的催化反应及机理,同时对其的生理功能也作了较祥细的讨论。     

水介质中有机反应的最新研究进展

水介质中的有机反应是形成碳-碳键的有效方法之一，近几年来一直是有机合成的研究热点．本文综述了近年来对水介质中的有机反应的研究成果，包括缩合反应、亲核加成反应、环加成反应、Barbier反应和多组分反应等，及其在有机合成中的应用研究进展．     

吡啶,异喹啉的氰亚甲基叶立德与烯烃的反应

报道了吡啶、异喹啉的氰亚甲基叶立德与取代烯烃的反应．用合成的溴乙腈与吡啶、异喹啉反应生成盐，转化为叶立德后，再与取代烯烃反应，合成了６个３酰氨基中氮茚衍生物．产物的结构经元素分析、ＩＲ、ＮＭＲ、ＭＳ鉴定．讨论了反应中氰基的水解及中氮茚衍生物的特征．     

Trans-SNARE pairing can precede a hemifusion intermediate in intracellular membrane fusion

The question concerning whether all membranes fuse according to the same mechanism has yet to be answered satisfactorily. During fusion of model membranes or viruses, membranes dock, the outer membrane leaflets mix (termed hemifusion), and finally the fusion pore opens and the contents mix. Viral fusion proteins consist of a membrane-disturbing 'fusion peptide' and a helical bundle that pin the membranes together. Although SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes form helical bundles with similar topology, it is unknown whether SNARE-dependent fusion events on intracellular membranes proceed through a hemifusion state. Here we identify the first hemifusion state for SNARE-dependent fusion of native membranes, and place it into a sequence of molecular events: formation of helical bundles by SNAREs precedes hemifusion; further progression to pore opening requires additional peptides. Thus, SNARE-dependent fusion may proceed along the same pathway as viral fusion: both use a docking mechanism via helical bundles and additional peptides to destabilize the membrane and efficiently induce lipid mixing. Our results suggest that a common lipidic intermediate may underlie all fusion reactions of lipid bilayers.