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Pepstatin (Pepstatin A) 是由放线菌类产生的一种特异性的天冬氨酸蛋白酶 (aspartic proteases) 抑制剂，能够抑制 hemoglobin-pepsin，hemoglobin-proctase，casein-pepsin，casein-proctase，casein-acid protease 和 hemoglobin-acid protease 的活性，IC50 值分别为 4.5 nM，6.2 nM，150 nM，290 nM，520 nM 和 260 nM；同时可抑制 HIV protease 的活性。

Pepstatin (Pepstatin A) is a specific aspartic protease inhibitor produced by actinomycetes, with IC50s of 4.5 nM, 6.2 nM, 150 nM, 290 nM, 520 nM and 260 nM for hemoglobin-pepsin, hemoglobin-proctase, casein-pepsin, casein-proctase, casein-acid protease and hemoglobin-acid protease, respectively. Pepstatin Ammonium also inhibits HIV protease.

Pepstatin A was originally purified from Actinomycetes species. The peptide is unusual in containing the amino acid statine (4-amino-hydroxy-6-methylheptanoic acid also known as AMHA). Pepstatin A competitively binds with acid proteases in a highly selective reversible manner to inhibit protease activity. Pepstatin A is ineffective on thiol, neutral and serine proteases. The functions of proteases have been investigated by the application of pepstatin A such as renin, pepsin, bovine chymosin and retroviral proteases from HIV. Characterisation of HIV protease using pepstatin A has been vital in development of HIV treatment to block viral replication. Pepstatin A is also a reagent to disrupt autophagy- this helps characterise the function of proteosome degradation in research such as during influenza A replication and improving drug delivery of therapeutic cancer treatments.

Pepstatin A is a natural product that inhibits the activity of proteases, particularly chymotrypsin and trypsin. It binds to the active site of these enzymes, blocking access to their substrate. Pepstatin A has been shown to have synergistic effects with other drugs in vitro, such as dapsone and clindamycin. Pepstatin A has inhibitory properties against infectious diseases, including HIV-1 and HIV-2, influenza virus type A (H1N1), herpes simplex virus type 1 (HSV-1), human papilloma virus type 18 (HPV-18), hepatitis C virus (HCV) types 1a and 1b, as well as dengue fever virus. Pepstatin A is also effective in inhibiting polymerase chain reaction amplification of mitochondrial DNA from patients with mitochondrial disorders. The biological sample for this research was obtained from calf thymus tissue. The natural compound pepstatin A has

"Pepstatin A is a natural product that has been synthesized for use as an inhibitor of proteolytic enzymes. It inhibits the activity of a wide range of proteases and is used in vitro to study the biochemical properties of these enzymes. Pepstatin A inhibits the activity of many important proteases, including those involved in infectious diseases, such as HIV and hepatitis C virus. Pepstatin A binds to the active site on serine proteases, blocking access by their substrates and thereby inhibiting enzyme activity. The binding site is highly conserved among different types of serine protease, with approximately 90% homology between trypsin and chymotrypsin. The inhibitory mechanism involves a specific interaction between pepstatin As hydrophobic side chain and the catalytic triad residues His57, Asp102, and Ser195 in trypsin or His57, Asp102, and Ser188 in chymotrypsin."

胃泌素(Gastrin)的定义

胃泌素是胃酸分泌的主要生理调节剂。它对胃粘膜也有重要的营养或生长促进作用。

Gastrin is a major physiological regulator of gastric acid secretion. It also has an important trophic or growth-promoting influence on the gastric mucosa.

胃泌素(Gastrin)的相关肽

前胃泌素在胃窦G细胞中合成并加工成许多生物活性肽。七肽胃泌素-17是主要产物（胃泌素成分3或少量胃泌素），也称为胆囊收缩素B【1】。胃泌素-17酰胺对应于前胃泌素-（55-71）。甘氨酸延伸的非硫酸化胃泌素-17对应于前胃泌素-（55-72）。胃泌素-17的一小部分在G细胞中被切割并作为短COOH末端肽释放，作为胃泌素-7，胃泌素-6和胃泌素-5的混合物【2】。硫酸化胃泌素-6是释放到窦静脉血中的主要形式。胃泌素6比胃泌素17具有更高的效力但功效更低。酪氨酸O-硫酸化增加了胃泌素-6的功效，这也增强了对消除的保护作用。隐球菌素对应于前胃泌素-（1-35）。隐球菌素-（6-35）（前胃泌素-（6-35））是该肽的较短形式【3】。两种最大的α-羧酰胺化胃泌素前体产物是胃泌素71和胃泌素52。胃泌素-52具有生物活性，其功效接近或类似于胃泌素-17【4】。胃泌素成分1是胃泌素的最大激素活性形式，并且已显示对应于胃泌素71。胃泌素-14被称为胃泌素成分4或微胃泌素【5】。五肽胃泌素对应于胃泌素的五个C末端氨基酸，与CCK-5（胆囊收缩素-5）相同，CCK-5主要通过B型胆囊收缩素受体起作用。

Progastrin is synthesized in antral G cells and processed into a number of bioactive peptides. The heptadecapeptide gastrin-17 is the main product (Gastrin component 3 or little Gastrin), called also Cholecystokinin B【1】. Gastrin-17 amide corresponds to Progastrin-(55-71). Glycine-extended nonsulfated gastrin-17 corresponds to Progastrin-(55-72).  A minor fraction of gastrin-17 is cleaved in G cells and released as short COOH-terminal peptides, as a mixture of gastrin-7, gastrin-6, and gastrin-5【2】. The sulfated gastrin-6 is the predominant form released to antral venous blood. Gastrin 6 has a higher potency but a lower efficacy than gastrin-17. The efficacy of gastrin-6 is increased by tyrosine O-sulfation, which also enhances the protection against elimination. Cryptagastrin corresponds to progastrin-(1-35). Cryptagastrin-(6-35) (progastrin-(6-35) is a shorter form of this peptide【3】. The two largest alpha-carboxyamidated progastrin products are gastrin-71 and gastrin-52. Gastrin-52 is bioactive with an efficacy close to or similar to that of gastrin-17【4】. Gastrin component 1 is the largest hormonally active form of gastrin and has been shown to correspond to gastrin-71. Gastrin-14 has been termed gastrin component 4 or minigastrin【5】. Pentagastrin corresponds the five C-terminal amino acids of gastrin and is the same as CCK-5 [cholecystokinin-5], which acts mainly through the type B cholecystokinin receptor.

胃泌素(Gastrin)的发现

胃泌素最初由Edkins和Cantab于1905【6】年鉴定，是胃窦中产生的一种刺激胃酸分泌的因子。它是从猪胃窦粘膜中纯化出来的，并于1964年由Gregory和Tracy测序【7】。

Gastrin was identified originally by Edkins and Cantab in 1905【6】, as a factor produced in the antrum of the stomach that stimulates gastric acid secretion. It was purified from hog antral mucosa and sequenced by Gregory and Tracy in 1964【7】.

 
胃泌素(Gastrin)的结构特征

胃泌素是一种线性肽，合成为前胃泌素，前胃泌素，在胃窦G细胞中加工成许多不同长度的生物活性胃泌素，它们具有相同的含有活性位点的α-酰胺化C末端。胃泌素的活性位点是羧基末端四肽酰胺Trp-Met-Asp-Phe-NH2，所有生物活性片段都具有羧基末端六序列Tyr（SO4）-Gly-Trp-Met-Asp-Phe-NH2。氨基末端延伸的长度控制循环激素形式的代谢和清除。所有生物活性胃泌素肽都是羧酰胺化的，以非硫酸化和硫酸化形式存在【8】。

Gastrin is a linear peptide that is synthesized as a preprohormone, Progastrin, which is processed in antral G cells to a number of bioactive gastrins of different length, which share the same alpha-amidated C-terminus containing the active site. The active site of gastrin is the carboxyterminal tetrapeptide amide Trp-Met-Asp-Phe-NH2 and all bioactive fragments have the carboxyterminal hexasequence Tyr (SO4)-Gly-Trp-Met-Asp-Phe-NH2. The lengths of the aminoterminal extensions govern metabolism and clearance of the circulating hormone forms.  All bioactive gastrin peptides are carboxyamidated and exist in nonsulfated and sulfated forms【8】.

胃泌素(Gastrin)的作用机制

胃泌素受体也是结合胆囊收缩素的受体之一，被称为CCK-B受体。它是G蛋白偶联受体家族的成员。胃泌素的结合刺激细胞内Ca++的增加，蛋白激酶C的激活和肌醇磷酸的产生【9】。

The gastrin receptor is also one of the receptors that bind cholecystokinin, and is known as the CCK-B receptor. It is a member of the G protein-coupled receptor family. Binding of gastrin stimulates an increase in intracellular Ca++, activation of protein kinase C, and production of inositiol phosphate【9】.

胃泌素(Gastrin)的功能

胃泌素似乎对胃肠功能至少有两个主要影响：

Gastrin appears to have at least two major effects on gastrointestinal function:

1、刺激胃酸分泌：胃泌素受体存在于壁细胞上，胃泌素与组胺和乙酰胆碱的结合导致这些细胞完全刺激酸分泌。肠嗜铬样（ECL）细胞也携带胃泌素受体，最近的证据表明，该细胞可能是胃泌素调节酸分泌的最重要靶标。胃泌素刺激ECL细胞导致组胺释放，组胺与壁细胞上的H2受体结合是全面分泌酸所必需的。

1. Stimulation of gastric acid secretion: Gastrin receptors are found on parietal cells, and binding of gastrin, along with histamine and acetylcholine, leads to fully-stimulated acid secretion by those cells. Enterochromaffin-like (ECL) cells also bear gastrin receptors, and recent evidence indicates that this cell may be the most important target of gastrin with regard to regulating acid secretion. Stimulation of ECL cells by gastrin leads to histamine release, and histamine binding to H2 receptors on parietal cells is necessary for full-blown acid secretion.

2、促进胃粘膜生长：胃泌素显然具有刺激胃粘膜发育和生长的许多方面的能力。胃泌素治疗可刺激胃粘膜中的DNA，RNA和蛋白质合成，并增加壁细胞的数量。支持这一功能的另一个观察结果是，患有高胃泌素血症（胃泌素异常高的血液水平）的人始终表现出胃粘膜肥大。

2. Promotion of gastric mucosal growth: Gastrin clearly has the ability to stimulate many aspects of mucosal development and growth in the stomach. Treatment with gastrin stimulates DNA, RNA and protein synthesis in gastric mucosa and increases the number of parietal cells. Another observation supporting this function is that humans with hypergastrinemia (abnormally high blood levels of gastrin) consistently show gastric mucosal hypertrophy.

除了壁细胞和ECL细胞靶标外，胃泌素还通过与胆囊收缩素受体结合来刺激胰腺腺泡细胞，并且已经在某些胃平滑肌细胞群上证实了胃泌素受体，这支持了药理学研究，证明了胃泌素在调节胃动力中的作用。

In addition to parietal and ECL cell targets, gastrin also stimulates pancreatic acinar cells via binding to cholecystokinin receptors, and gastrin receptors have been demonstrated on certain populations of gastric smooth muscle cells, supporting pharmacologic studies that demonstrate a role for gastrin in regulating gastric motility.

胃泌素(Gastrin)的相关文献

1. Morley JS, Tracy HJ, Gregory RA (1965). Structure-function relationships in the active C-terminal tetrapeptide sequence of gastrin. Nature, 207, 1356-1359.
2. Rehfeld JF, Hansen CP, Johnsen AH (1995). Postpoly(Glu) cleavage and degradation modified by O-sulfated tyrosine: a novel posttranslational processing mechanism. EMBO Journal, 14, 389-396.
3. Huebner VD, Jiang RL, Lee TD, Legesse K, Walsh JH, Shively JE, Chew P, Azumi T, Reeve JR Jr (1991). Purification and structural characterization of progastrin-derived peptides from a human gastrinoma. J Biol. Chem., 266(19), 12223-12227.
4. Hansen CP, Stadil F, Rehfeld JF (1995). Metabolism and influence of gastrin-52 on gastric acid secretion in humans. Amer. J of Physiol., 269(4 Pt 1), G600-605.
5. Gregory RA, Tracy HJ, Harris JI, Runswick MJ, Moore S, Kenner GW, Ramage R (1979). Minigastrin: corrected structure and synthesis. Hoppe Seylers Zeitschrift für Physiologische Chemie, 360, 73-80.
6. Edkin JS and Cantab MB (1905). On the chemical mechanism of gastric secretion. Proc. of the Royal Society London, 76, 376.
7. Gregory H, Hardy PM, Jones DS, Kenner GW, Sheppard RC (1964). The antral hormone gastrin. Structure of gastrin. Nature, 204, 931-3.
8. Rehfeld JF and Larsson LI (1979). The predominating molecular form of gastrin and cholecystokinin in the gut is a small peptide corresponding to their COOH-terminal tetrapeptide amide. Acta Physiologica Scandinavia, 115, 117-119.
9. Dockray GJ (1999). Topical review. gastrin and gastric epithelial physiology. J Physiol., 518(2), 315-324.

烷基化肽-说明

专肽生物可提供多肽烷基化修饰，增加多肽一端的疏水性，例如常见的C18，C16，C14，C12，以及C6等，也可根据客户要求，接其他长度的烷基化链。

定义
酶是用于生化反应的非常有效的催化剂。它们通过提供较低活化能的替代反应途径来加快反应速度。酶作用于底物并产生产物。一些物质降低或什至停止酶的催化活性被称为抑制剂。
发现
1965年，Umezawa H分析了微生物产生的酶抑制剂，并分离出了抑制亮肽素和抗痛药的胰蛋白酶和木瓜蛋白酶，乳糜蛋白酶抑制的胰凝乳蛋白酶，胃蛋白酶抑制素抑制胃蛋白酶，泛磷酰胺抑制唾液酸酶，乌藤酮抑制酪氨酸羟化酶，多巴汀抑制多巴胺3-羟硫基嘧啶和多巴胺3-羟色胺酶酪氨酸羟化酶和多巴胺J3-羟化酶。最近，一种替代方法已应用于预测新的抑制剂：合理的药物设计使用酶活性位点的三维结构来预测哪些分子可能是抑制剂1。已经开发了用于识别酶抑制剂的基于计算机的方法，例如分子力学和分子对接。
结构特征
已经确定了许多抑制剂的晶体结构。已经确定了三种与凝血酶复合的高效且选择性的低分子量刚性肽醛醛抑制剂的晶体结构。这三种抑制剂全部在P3位置具有一个新的内酰胺部分，而对胰蛋白酶选择性最高的两种抑制剂在P1位置具有一个与S1特异性位点结合的胍基哌啶基。凝血酶的抑制动力学从慢到快变化，而对于胰蛋白酶，抑制的动力学在所有情况下都快。根据两步机理2中稳定过渡态络合物的缓慢形成来检验动力学。
埃米尔•菲舍尔（Emil Fischer）在1894年提出，酶和底物都具有特定的互补几何形状，彼此恰好契合。这称为“锁和钥匙”模型3。丹尼尔·科什兰（Daniel Koshland）提出了诱导拟合模型，其中底物和酶是相当灵活的结构，当底物与酶4相互作用时，活性位点通过与底物的相互作用不断重塑。
在众多生物活性肽的成熟过程中，需要由其谷氨酰胺（或谷氨酰胺）前体形成N末端焦谷氨酸（pGlu）。游离形式并与底物和三种咪唑衍生抑制剂结合的人QC的结构揭示了类似于两个锌外肽酶的α/β支架，但有多个插入和缺失，特别是在活性位点区域。几种活性位点突变酶的结构分析为针对QC相关疾病5的抑制剂的合理设计提供了结构基础。
作用方式
酶是催化化学反应的蛋白质。酶与底物相互作用并将其转化为产物。抑制剂的结合可以阻止底物进入酶的活性位点和/或阻止酶催化其反应。抑制剂的种类繁多，包括：非特异性，不可逆，可逆-竞争性和非竞争性。可逆抑制剂 以非共价相互作用（例如疏水相互作用，氢键和离子键）与酶结合。非特异性抑制方法包括最终使酶的蛋白质部分变性并因此不可逆的任何物理或化学变化。特定抑制剂 对单一酶发挥作用。大多数毒药通过特异性抑制酶发挥作用。竞争性抑制剂是任何与底物的化学结构和分子几何结构非常相似的化合物。抑制剂可以在活性位点与酶相互作用，但是没有反应发生。非竞争性抑制剂是与酶相互作用但通常不在活性位点相互作用的物质。非竞争性抑制剂的净作用是改变酶的形状，从而改变活性位点，从而使底物不再能与酶相互作用而产生反应。非竞争性抑制剂通常是可逆的。不可逆抑制剂与酶形成牢固的共价键。这些抑制剂可以在活性位点附近或附近起作用。
功能
工业应用中， 酶在商业上被广泛使用，例如在洗涤剂，食品和酿造工业中。蛋白酶用于“生物”洗衣粉中，以加速蛋白质在诸如血液和鸡蛋等污渍中的分解。商业上使用酶的问题包括：它们是水溶性的，这使得它们难以回收，并且一些产物可以抑制酶的活性（反馈抑制）。
药物分子，许多药物分子都是酶抑制剂，药用酶抑制剂通常以其特异性和效力为特征。高度的特异性和效力表明该药物具有较少的副作用和较低的毒性。酶抑制剂在自然界中发现，并且也作为药理学和生物化学的一部分进行设计和生产6。
天然毒物 通常是酶抑制剂，已进化为保护植物或动物免受天敌的侵害。这些天然毒素包括一些已知最剧毒的化合物。
神经气体（ 例如二异丙基氟磷酸酯（DFP））通过与丝氨酸的羟基反应生成酯，从而抑制了乙酰胆碱酯酶的活性位点。
参考
1、Scapin G (2006). Structural biology and drug discovery. Curr. Pharm. Des.,      12(17):2087–2097.
2、Krishnan R, Zhang E, Hakansson K, Arni RK, Tulinsky A, Lim-Wilby MS, Levy OE, Semple JE, Brunck TK (1998). Highly selective mechanism-based thrombin inhibitors:  structures of thrombin and trypsin inhibited with rigid peptidyl aldehydes. Biochemistry, 37 (35):12094-12103.
3、Fischer E (1894). Einfluss der configuration auf die wirkung der enzyme. Ber. Dt. Chem. Ges., 27:2985–2993.
4、Koshland DE (1958). Application of a theory of enzyme specificity to protein synthesis. PNAS., 44 (2):98–104.
5、Huang KF, Liu YL, Cheng WJ, Ko TP, Wang AH (2005). Crystal structures of human glutaminyl cyclase, an enzyme responsible for protein N-terminal pyroglutamate formation. PNAS., 102(37):13117-13122.
6、Holmes CF, Maynes JT, Perreault KR, Dawson JF, James MN (2002). Molecular enzymology underlying regulation of protein phosphatase-1 by natural toxins. Curr Med Chem., 9(22):1981-1989.

Definition
Enzymes are very efficient catalysts for biochemical reactions. They speed up reactions by providing an alternative reaction pathway of lower activation energy. Enzyme acts on substrate and gives rise to a product. Some substances reduce or even stop the catalytic activities of enzymes are called inhibitors.

Discovery
In 1965, Umezawa H analysed enzyme inhibitors produced by microorganisms and isolated leupeptin and antipain inhibiting trypsin and papain, chymostatin inhibiting chymotrypsin, pepstatin inhibiting pepsin, panosialin inhibiting sialidases, oudenone inhibiting tyrosine hydroxylase, dopastin inhibiting dopamine 3-hydroxylase, aquayamycin and chrothiomycin inhibiting tyrosine hydroxylase and dopamine J3-hydroxylase . Recently, an alternative approach has been applied to predict new inhibitors: rational drug design uses the three-dimensional structure of an enzyme's active site to predict which molecules might be inhibitors 1. Computer-based methods for identifying inhibitor for an enzyme have been developed, such as molecular mechanics and molecular docking.

Structural Characteristics
The crystal structures of many inhibitors have been determined. The crystal structures of three highly potent and selective low-molecular weight rigid peptidyl aldehyde inhibitors complexed with thrombin have been determined. All the three inhibitors have a novel lactam moiety at the P3 position, while the two with greatest trypsin selectivity have a guanidinopiperidyl group at the P1 position that binds in the S1 specificity site. The kinetics of inhibition vary from slow to fast with thrombin and are fast in all cases with trypsin. The kinetics are examined in terms of the slow formation of a stable transition-state complex in a two-step mechanism 2.

Emil Fischer in 1894 suggested that both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another.This is known as "the lock and key" model 3. Daniel Koshland suggested induced fit model where substrate and enzymes are rather flexible structures, the active site is continually reshaped by interactions with the substrate as the substrate interacts with the enzyme 4.

N-terminal pyroglutamate (pGlu) formation from its glutaminyl (or glutamyl) precursor is required in the maturation of numerous bioactive peptides. The structure of human QC in free form and bound to a substrate and three imidazole-derived inhibitors reveals an alpha/beta scaffold akin to that of two-zinc exopeptidases but with several insertions and deletions, particularly in the active-site region. The structural analyses of several active-site-mutant enzymes provide a structural basis for the rational design of inhibitors against QC-associated disorders 5.

Mode of Action
Enzymes are proteins that catalyze chemical reactions. Enzymes interact with substrate and convert them into products. Inhibitor binding can stop a substrate from entering the enzyme's active site and/or hinder the enzyme from catalyzing its reaction. There are a variety of types of inhibitors including: nonspecific, irreversible, reversible - competitive and noncompetitive. Reversible inhibitors bind to enzymes with non-covalent interactions like hydrophobic interactions, hydrogen bonds, and ionic bonds. Non-specific methods of inhibition include any physical or chemical changes which ultimately denature the protein portion of the enzyme and are therefore irreversible. Specific Inhibitors exert their effects upon a single enzyme. Most poisons work by specific inhibition of enzymes. A competitive inhibitor is any compound which closely resembles the chemical structure and molecular geometry of the substrate. The inhibitor may interact with the enzyme at the active site, but no reaction takes place. A noncompetitive inhibitor is a substance that interacts with the enzyme, but usually not at the active site.  The net effect of a non competitive inhibitor is to change the shape of the enzyme and thus the active site, so that the substrate can no longer interact with the enzyme to give a reaction. Non competitive inhibitors are usually reversible. Irreversible Inhibitors form strong covalent bonds with an enzyme.  These inhibitors may act at, near, or remote from the active site .

Functions
Industrial application, enzymes are widely used commercially, for example in the detergent, food and brewing industries. Protease enzymes are used in 'biological' washing powders to speed up the breakdown of proteins in stains like blood and egg. Problems using enzymes commercially include: they are water soluble which makes them hard to recover and some products can inhibit the enzyme activity (feedback inhibition) .

Drug molecules, many drug molecules are enzyme inhibitors and a medicinal enzyme inhibitor is usually characterized by its specificity and its potency. A high specificity and potency suggests that a drug will have fewer side effects and less toxic. Enzyme inhibitors are found in nature and are also designed and produced as part of pharmacology and biochemistry 6.

Natural poisons are often enzyme inhibitors that have evolved to defend a plant or animal against predators. These natural toxins include some of the most poisonous compounds known.

Nerve gases such as diisopropylfluorophosphate (DFP) inhibit the active site of acetylcholine esterase by reacting with the hydroxyl group of serine to make an ester.

References

Scapin G (2006). Structural biology and drug discovery. Curr. Pharm. Des.,      12(17):2087–2097.

Krishnan R, Zhang E, Hakansson K, Arni RK, Tulinsky A, Lim-Wilby MS, Levy OE, Semple JE, Brunck TK (1998). Highly selective mechanism-based thrombin inhibitors:  structures of thrombin and trypsin inhibited with rigid peptidyl aldehydes. Biochemistry, 37 (35):12094-12103.

Fischer E (1894). Einfluss der configuration auf die wirkung der enzyme. Ber. Dt. Chem. Ges., 27:2985–2993.

Koshland DE (1958). Application of a theory of enzyme specificity to protein synthesis. PNAS., 44 (2):98–104.

Huang KF, Liu YL, Cheng WJ, Ko TP, Wang AH (2005). Crystal structures of human glutaminyl cyclase, an enzyme responsible for protein N-terminal pyroglutamate formation. PNAS., 102(37):13117-13122.

Holmes CF, Maynes JT, Perreault KR, Dawson JF, James MN (2002). Molecular enzymology underlying regulation of protein phosphatase-1 by natural toxins. Curr Med Chem., 9(22):1981-1989.