出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/02/23 16:35:37」(JST)
| プロリン | |
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IUPAC名
Proline |
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系統名
Pyrrolidine-2-carboxylic acid[1]
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| 識別情報 | |
| CAS登録番号 | 609-36-9 , 344-25-2 (2R)-カルボン酸 , 147-85-3 (2S)-カルボン酸 |
| PubChem | 614, 8988 (2R)-カルボン酸, 145742 (2S)-カルボン酸 |
| ChemSpider | 594 , 8640 (2R)-カルボン酸 , 128566 (2S)-カルボン酸 |
| UNII | DCS9E77JPQ |
| EINECS | 210-189-3 |
| DrugBank | DB02853 |
| KEGG | C16435 |
| MeSH | Proline |
| ChEBI | CHEBI:26271 |
| ChEMBL | CHEMBL72275 |
| RTECS番号 | TW3584000 |
| バイルシュタイン | 80812 |
| Gmelin参照 | 26927 |
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SMILES
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InChI
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| 特性 | |
| 化学式 | C5H9NO2 |
| モル質量 | 115.13 g mol−1 |
| 精密質量 | 115.063328537 g mol-1 |
| 外観 | 透明な結晶 |
| 融点 |
205-228 °C, 478-501 K, 401-442 °F (分解) |
| log POW | -0.06 |
| 酸解離定数 pKa | 2.351 |
| 危険性 | |
| Sフレーズ | S22, S24/25 |
| 特記なき場合、データは常温 (25 °C)・常圧 (100 kPa) におけるものである。 | |
プロリン(proline)はアミノ酸の一つ。
ピロリジン-2-カルボン酸のこと。スペルはprolineで、略号はProまたはP。環状アミノ酸で、タンパク質を構成する。糖原性を持つ。唯一アミノ基を持たないアミノ酸。通常のアミノ酸に存在するα位の炭素に存在するアミノ基はこのプロリンの場合のみイミノ基となっているために、本来はイミノ酸と分類されるべきであり、厳密にはアミノ酸に含めるべきではないのではないかという議論がある。
表皮細胞増殖促進活性、コラーゲン合成促進活性、角質層保湿作用などの生理活性を示す。 一度破壊されたコラーゲンを修復する力をもつアミノ酸。体の結合組織、心筋の合成時の主な材料でもある。最近では、アルドール反応の安全かつ効果的な触媒として注目されつつある。
生体内では、主に肝臓と小腸で行われるが、それぞれ合成経路が少し異なる。肝臓では、尿素回路の中間体であるオルニチンより、オルニチン-オキソ酸アミノトランスフェラーゼ (EC 2.6.1.13) とピロリン-5-カルボン酸レダクターゼ (EC 1.5.1.2) の作用により合成される。ただし、両酵素の間に、非酵素的に進む側鎖の閉環反応が含まれている。
EC 2.6.1.13 L-ornithine + a 2-oxo acid = L-glutamate 5-semialdehyde + an L-amino acid
非酵素的 L-glutamate 5-semialdehyde = 1-pyrroline-5-carboxylate + H2O
EC 1.5.1.2 1-pyrroline-5-carboxylate + NAD(P)H + H+ = L-proline + NAD(P)+
小腸では、グルタミンまたはグルタミン酸からオルニチンが合成され、以降は肝臓と同じ経路による。
2000年、アルドール反応を触媒する酵素アルドラーゼの研究を進めていたリスト、バルバス、ラーナーらは、大きなタンパク質ではなくプロリン自身が高収率・高エナンチオ選択的なアルドール反応を触媒することを見出した。[要出典]プロリンの二級アミン部分がカルボニル化合物とエナミンを形成し、これがもう一分子のカルボニル化合物と反応することでアルドール反応を進行させると考えられている。
その後アルドール反応以外にもマイケル反応・マンニッヒ反応などにもプロリン触媒が適用できることが分かり、大いに研究が進展した。金属を持たない触媒（有機分子触媒）として近年大いに注目されている分野である。
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| Proline | |
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IUPAC name
Proline |
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Systematic name
Pyrrolidine-2-carboxylic acid[1] |
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| Identifiers | |
| CAS number | 609-36-9 Y, 344-25-2 (R) Y, 147-85-3 (S) Y |
| PubChem | 614, 8988 (R), 145742 (S) |
| ChemSpider | 594 Y, 8640 (R) Y, 128566 (S) Y |
| UNII | DCS9E77JPQ Y |
| EC number | 210-189-3 |
| DrugBank | DB02853 |
| KEGG | C16435 Y |
| MeSH | Proline |
| ChEBI | CHEBI:26271 Y |
| ChEMBL | CHEMBL72275 Y |
| RTECS number | TW3584000 |
| Beilstein Reference | 80812 |
| Gmelin Reference | 26927 |
| Jmol-3D images | Image 1 Image 2 |
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SMILES
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InChI
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| Properties | |
| Molecular formula | C5H9NO2 |
| Molar mass | 115.13 g mol−1 |
| Appearance | Transparent crystals |
| Melting point | 205 to 228 °C; 401 to 442 °F; 478 to 501 K (decomposes) |
| Solubility | 1.5g/100g ethanol 19 degC[2] |
| log P | -0.06 |
| Acidity (pKa) | 1.99 (carboxyl), 10.96 (amino)[3] |
| Hazards | |
| MSDS | External MSDS |
| S-phrases | S22, S24/25 |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa) |
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| Infobox references | |
Proline (abbreviated as Pro or P) is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the amine nitrogen is bound to not one but two alkyl groups, thus making it a secondary amine. The more common L form has S stereochemistry.
Proline is biosynthetically derived from the amino acid L-glutamate and its immediate precursor is the imino acid (S)-1-pyrroline-5-carboxylate (P5C). Enzymes involved in a typical biosynthesis include:[4]
The distinctive cyclic structure of proline's side chain gives proline an exceptional conformational rigidity compared to other amino acids. It also affects the rate of peptide bond formation between proline and other amino acids. When proline is bound as an amide in a peptide bond, its nitrogen is not bound to any hydrogen, meaning it cannot act as a hydrogen bond donor, but can be a hydrogen bond acceptor.
Peptide bond formation with incoming Pro-tRNAPro is considerably slower than with any other tRNAs, which is a general feature of N-alkylamino acids.[5] Peptide bond formation is also slow between an incoming tRNA and a chain ending in proline; with the creation of proline-proline bonds slowest of all.[6]
The exceptional conformational rigidity of proline affects the secondary structure of proteins near a proline residue and may account for proline's higher prevalence in the proteins of thermophilic organisms. Protein secondary structure can be described in terms of the dihedral angles φ, ψ and ω of the protein backbone. The cyclic structure of proline's side chain locks the angle φ at approximately −60°.
Proline acts as a structural disruptor in the middle of regular secondary structure elements such as alpha helices and beta sheets; however, proline is commonly found as the first residue of an alpha helix and also in the edge strands of beta sheets. Proline is also commonly found in turns (another kind of secondary structure), and aids in the formation of beta turns. This may account for the curious fact that proline is usually solvent-exposed, despite having a completely aliphatic side chain.
Multiple prolines and/or hydroxyprolines in a row can create a polyproline helix, the predominant secondary structure in collagen. The hydroxylation of proline by prolyl hydroxylase (or other additions of electron-withdrawing substituents such as fluorine) increases the conformational stability of collagen significantly.[7] Hence, the hydroxylation of proline is a critical biochemical process for maintaining the connective tissue of higher organisms. Severe diseases such as scurvy can result from defects in this hydroxylation, e.g., mutations in the enzyme prolyl hydroxylase or lack of the necessary ascorbate (vitamin C) cofactor.
Sequences of proline and 2-aminoisobutyric acid (Aib) also form a helical turn structure.[citation needed]
Peptide bonds to proline, and to other N-substituted amino acids (such as sarcosine), are able to populate both the cis and trans isomers. Most peptide bonds overwhelmingly adopt the trans isomer (typically 99.9% under unstrained conditions), chiefly because the amide hydrogen (trans isomer) offers less steric repulsion to the preceding atom than does the following atom (cis isomer). By contrast, the cis and trans isomers of the X-Pro peptide bond (where X represents any amino acid) both experience steric clashes with the neighboring substitution and are nearly equal energetically. Hence, the fraction of X-Pro peptide bonds in the cis isomer under unstrained conditions ranges from 10-40%; the fraction depends slightly on the preceding amino acid, with aromatic residues favoring the cis isomer slightly.
From a kinetic standpoint, cis-trans proline isomerization is a very slow process that can impede the progress of protein folding by trapping one or more proline residues crucial for folding in the non-native isomer, especially when the native protein requires the cis isomer. This is because proline residues are exclusively synthesized in the ribosome as the trans isomer form. All organisms possess prolyl isomerase enzymes to catalyze this isomerization, and some bacteria have specialized prolyl isomerases associated with the ribosome. However, not all prolines are essential for folding, and protein folding may proceed at a normal rate despite having non-native conformers of many X-Pro peptide bonds.
Proline and its derivatives are often used as asymmetric catalysts in organic reactions. The CBS reduction and proline catalysed aldol condensation are prominent examples.
L-Proline is an osmoprotectant and therefore is used in many pharmaceutical, biotechnological applications.
In brewing, proteins rich in proline combine with polyphenols to produce haze (turbidity).[8]
Proline is one of the two amino acids that do not follow along with the typical Ramachandran plot, along with glycine. Due to the ring formation connected to the beta carbon, the ψ and φ angles about the peptide bond have fewer allowable degrees of rotation. As a result it is often found in "turns" of proteins as its free entropy (ΔS) is not as comparatively large to other amino acids and thus in a folded form vs. unfolded form, the change in entropy is less. Furthermore, proline is rarely found in α and β structures as it would reduce the stability of such structures, because its side chain α-N can only form one hydrogen bond.
Additionally, proline is the only amino acid that does not form a blue/purple colour when developed by spraying with ninhydrin for uses in chromatography. Proline, instead, produces an orange/yellow colour.
Richard Willstätter synthesized proline by the reaction of sodium salt of diethyl malonate with 1,3-dibromopropane in 1900. In 1901, Hermann Emil Fischer isolated proline from casein and the decomposition products of γ-phthalimido-propylmalonic ester.[9]
Racemic proline can be synthesized from diethyl malonate and acrylonitrile:[10]
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| リンク元 | 「プロリン」「P」「L-proline」 |
| 拡張検索 | 「proline oxidase」「procollagen-proline dioxygenase」「proline residue」「hydroxyproline」 |