Peptide

Short chains of 2–50 amino acids

"Peptides" redirects here. For the journal, see Peptides (journal).

Drosomycin, an example of a peptide

Peptides are short chains of amino acids linked by peptide bonds.[1][2] A polypeptide is a longer, continuous, unbranched peptide chain.[3] Polypeptides that have a molecular mass of 10,000 Da or more are called proteins.[4] Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.

Peptides fall under the broad chemical classes of biological polymers and oligomers, alongside nucleic acids, oligosaccharides, polysaccharides, and others.

Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to ligands such as coenzymes and cofactors, to another protein or other macromolecule such as DNA or RNA, or to complex macromolecular assemblies.[5]

Amino acids that have been incorporated into peptides are termed residues. A water molecule is released during formation of each amide bond.[6] All peptides except cyclic peptides have an N-terminal (amine group) and C-terminal (carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image).

## Classification

[edit]

There are numerous types of peptides that have been classified according to their sources and functions. According to the Handbook of Biologically Active Peptides, some groups of peptides include plant peptides, bacterial/antibiotic peptides, fungal peptides, invertebrate peptides, amphibian/skin peptides, venom peptides, cancer/anticancer peptides, vaccine peptides, immune/inflammatory peptides, brain peptides, endocrine peptides, ingestive peptides, gastrointestinal peptides, cardiovascular peptides, renal peptides, respiratory peptides, opioid peptides, neurotrophic peptides, and blood–brain peptides.[7]

Some ribosomal peptides are subject to proteolysis. These function, typically in higher organisms, as hormones and signaling molecules. Some microbes produce peptides as antibiotics, such as microcins and bacteriocins.[8]

Peptides frequently have post-translational modifications such as phosphorylation, hydroxylation, sulfonation, palmitoylation, glycosylation, and disulfide formation. In general, peptides are linear, although lariat structures have been observed.[9] More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in platypus venom.[10]

Nonribosomal peptides are assembled by enzymes, not the ribosome. A common non-ribosomal peptide is glutathione, a component of the antioxidant defenses of most aerobic organisms.[11] Other nonribosomal peptides are most common in unicellular organisms, plants, and fungi and are synthesized by modular enzyme complexes called nonribosomal peptide synthetases.[12]

These complexes are often laid out in a similar fashion, and they can contain many different modules to perform a diverse set of chemical manipulations on the developing product.[13] These peptides are often cyclic and can have highly complex cyclic structures, although linear nonribosomal peptides are also common. Since the system is closely related to the machinery for building fatty acids and polyketides, hybrid compounds are often found. The presence of oxazoles or thiazoles often indicates that the compound was synthesized in this fashion.[14]

Peptones are derived from animal milk or meat digested by proteolysis.[15] In addition to containing small peptides, the resulting material includes fats, metals, salts, vitamins, and many other biological compounds. Peptones are used in nutrient media for growing bacteria and fungi.[16]

Peptide fragments refer to fragments of proteins that are used to identify or quantify the source protein.[17] Often these are the products of enzymatic degradation performed in the laboratory on a controlled sample, but can also be forensic or paleontological samples that have been degraded by natural effects.[18][19]

## Chemical synthesis

[edit]

Main article: Peptide synthesis

Solid-phase peptide synthesis on a rink amide resin using Fmoc-α-amine-protected amino acid

## Protein-peptide interactions

[edit]

Example of a protein (orange) and peptide (green) interaction. Obtained from Propedia: a peptide-protein interactions database.[20]

Peptides can perform interactions with proteins and other macromolecules. They are responsible for numerous important functions in human cells, such as cell signaling, and act as immune modulators.[21] Indeed, studies have reported that 15-40% of all protein-protein interactions in human cells are mediated by peptides.[22] Additionally, it is estimated that at least 10% of the pharmaceutical market is based on peptide products.[21]

## Example families

[edit]

The peptide families in this section are ribosomal peptides, usually with hormonal activity. All of these peptides are synthesized by cells as longer "propeptides" or "proproteins" and truncated prior to exiting the cell. They are released into the bloodstream where they perform their signaling functions.

### Antimicrobial peptides

[edit]

* Magainin family
* Cecropin family
* Cathelicidin family
* Defensin family

### Tachykinin peptides

[edit]

Main article: Tachykinin peptides

* Substance P
* Kassinin
* Neurokinin A
* Eledoisin
* Neurokinin B

### Vasoactive intestinal peptides

[edit]

Main article: Secretin family

* VIP (Vasoactive Intestinal Peptide; PHM27)
* PACAP Pituitary Adenylate Cyclase Activating Peptide
* Peptide PHI 27 (Peptide Histidine Isoleucine 27)
* GHRH 1-24 (Growth Hormone Releasing Hormone 1-24)
* Glucagon
* Secretin

### Pancreatic polypeptide-related peptides

[edit]

* NPY (NeuroPeptide Y)
* PYY (Peptide YY)
* APP (Avian Pancreatic Polypeptide)
* PPY Pancreatic PolYpeptide

### Opioid peptides

[edit]

Main article: Opioid peptide

* Proopiomelanocortin (POMC) peptides
* Enkephalin pentapeptides
* Prodynorphin peptides

### Calcitonin peptides

[edit]

* Calcitonin
* Amylin
* AGG01

### Self-assembling peptides

[edit]

* Aromatic short peptides[23][24]
* Biomimetic peptides[25]
* Peptide amphiphiles[26][27][28][29]
* Peptide dendrimers[30]

### Other peptides

[edit]

* B-type Natriuretic Peptide (BNP) – produced in the myocardium and useful in medical diagnosis
* Lactotripeptides – Lactotripeptides might reduce blood pressure,[31][32][33] although the evidence is mixed.[34]
* Peptidic components from traditional Chinese medicine Colla Corii Asini in hematopoiesis.[35]
* Jelleine – produced from royal jelly of honey bees.

## Terminology

[edit]

### Length

[edit]

Several terms related to peptides have no strict length definitions, and there is often overlap in their usage:

* A polypeptide is a single linear chain of many amino acids (any length), held together by amide bonds.
* A protein consists of one or more polypeptides (more than about 50 amino acids long).
* An oligopeptide consists of only a few amino acids (between two and twenty).

### Number of amino acids

[edit]

A tripeptide (example Val-Gly-Ala) with
green marked amino end (L-valine) and
blue marked carboxyl end (L-alanine)

Peptides and proteins are often described by the number of amino acids in their chain, e.g. a protein with 158 amino acids may be described as a "158 amino-acid-long protein". Peptides of specific shorter lengths are named using IUPAC numerical multiplier prefixes:

* A monopeptide has one amino acid.
* A dipeptide has two amino acids.
* A tripeptide has three amino acids.
* A tetrapeptide has four amino acids.
* A pentapeptide has five amino acids. (e.g., enkephalin).
* A hexapeptide has six amino acids. (e.g., angiotensin IV).
* A heptapeptide has seven amino acids. (e.g., spinorphin).
* An octapeptide has eight amino acids (e.g., angiotensin II).
* A nonapeptide has nine amino acids (e.g., oxytocin).
* A decapeptide has ten amino acids (e.g., gonadotropin-releasing hormone and angiotensin I).
* A undecapeptide has eleven amino acids (e.g., substance P).

The same words are also used to describe a group of residues in a larger polypeptide (e.g., RGD motif).

### Function

[edit]

* A neuropeptide is a peptide that is active in association with neural tissue.
* A lipopeptide is a peptide that has a lipid connected to it, and pepducins are lipopeptides that interact with GPCRs.
* A peptide hormone is a peptide that acts as a hormone.
* A proteose is a mixture of peptides produced by the hydrolysis of proteins. The term is somewhat archaic.
* A peptidergic agent (or drug) is a chemical which functions to directly modulate the peptide systems in the body or brain. An example is opioidergics, which are neuropeptidergics.
* A cell-penetrating peptide is a peptide able to penetrate the cell membrane.

## See also

[edit]

Wikiquote has quotations related to Peptide.

* Acetyl hexapeptide-3
* Beefy meaty peptide
* Collagen hybridizing peptide, a short peptide that can bind to denatured collagen in tissues
* Bis-peptide
* CLE peptide
* D-peptide
* Epidermal growth factor
* Journal of Peptide Science
* Lactotripeptides
* Micropeptide
* Multifunctional peptide
* Neuropeptide
* Palmitoyl pentapeptide-4
* Pancreatic hormone
* peptide spectral library
* Peptide synthesis
* Peptidomimetics (such as peptoids and β-peptides) to peptides, but with different properties.
* Protein tag, describing addition of peptide sequences to enable protein isolation or detection
* Replikins
* Ribosome
* Translation (biology)

## References

[edit]

1. ^ Hamley, I. W. (September 2020). introduction to Peptide Science. Wiley. ISBN 978-1-119-69817-3.
2. ^ Nelson, David L.; Cox, Michael M. (2005). Principles of Biochemistry (4th ed.). New York: W. H. Freeman. ISBN 0-7167-4339-6.
3. ^ Saladin, K. (13 January 2011). Anatomy & physiology: the unity of form and function (6th ed.). McGraw-Hill. p. 67\. ISBN 978-0-07-337825-1.
4. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006-) "proteins". doi:10.1351/goldbook.P04898.
5. ^ Ardejani, Maziar S.; Orner, Brendan P. (2013-05-03). "Obey the Peptide Assembly Rules". Science. 340 (6132): 561–562. Bibcode:2013Sci...340..561A. doi:10.1126/science.1237708. ISSN 0036-8075. PMID 23641105. S2CID 206548864.
6. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006-) "amino-acid residue in a polypeptide". doi:10.1351/goldbook.A00279.
7. ^ Abba J. Kastin, ed. (2013). Handbook of Biologically Active Peptides (2nd ed.). Elsevier Science. ISBN 978-0-12-385095-9.
8. ^ Duquesne S, Destoumieux-Garzón D, Peduzzi J, Rebuffat S (August 2007). "Microcins, gene-encoded antibacterial peptides from enterobacteria". Natural Product Reports. 24 (4): 708–34. doi:10.1039/b516237h. PMID 17653356.
9. ^ Pons M, Feliz M, Antònia Molins M, Giralt E (May 1991). "Conformational analysis of bacitracin A, a naturally occurring lariat". Biopolymers. 31 (6): 605–12. doi:10.1002/bip.360310604. PMID 1932561. S2CID 10924338.
10. ^ Torres AM, Menz I, Alewood PF, et al. (July 2002). "D-Amino acid residue in the C-type natriuretic peptide from the venom of the mammal, Ornithorhynchus anatinus, the Australian platypus". FEBS Letters. 524 (1–3): 172–6. doi:10.1016/S0014-5793(02)03050-8. PMID 12135762. S2CID 3015474.
11. ^ Meister A, Anderson ME; Anderson (1983). "Glutathione". Annual Review of Biochemistry. 52 (1): 711–60. doi:10.1146/annurev.bi.52.070183.003431. PMID 6137189.
12. ^ Hahn M, Stachelhaus T; Stachelhaus (November 2004). "Selective interaction between nonribosomal peptide synthetases is facilitated by short communication-mediating domains". Proceedings of the National Academy of Sciences of the United States of America. 101 (44): 15585–90. Bibcode:2004PNAS..10115585H. doi:10.1073/pnas.0404932101. PMC 524835. PMID 15498872.
13. ^ Finking R, Marahiel MA; Marahiel (2004). "Biosynthesis of nonribosomal peptides1". Annual Review of Microbiology. 58 (1): 453–88. doi:10.1146/annurev.micro.58.030603.123615. PMID 15487945.
14. ^ Du L, Shen B; Shen (March 2001). "Biosynthesis of hybrid peptide-polyketide natural products". Current Opinion in Drug Discovery & Development. 4 (2): 215–28. PMID 11378961.
15. ^ "UsvPeptides- USVPeptides is a leading pharmaceutical company in India". USVPeptides.
16. ^ Payne, J. W.; Rose, Anthony H.; Tempest, D. W. (27 September 1974). "Peptides and micro-organisms". Advances in Microbial Physiology, Volume 13. Vol. 13\. Oxford, England: Elsevier Science. pp. 55–160. doi:10.1016/S0065-2911(08)60038-7. ISBN 978-0-08-057971-9. OCLC 1049559483. PMID 775944.
17. ^ Hummel J, Niemann M, Wienkoop S, Schulze W, Steinhauser D, Selbig J, Walther D, Weckwerth W (2007). "ProMEX: a mass spectral reference database for proteins and protein phosphorylation sites". BMC Bioinformatics. 8 (1): 216. doi:10.1186/1471-2105-8-216. PMC 1920535. PMID 17587460.
18. ^ Webster J, Oxley D; Oxley (2005). "Peptide Mass Fingerprinting". Chemical Genomics. Methods in Molecular Biology. Vol. 310\. pp. 227–40. doi:10.1007/978-1-59259-948-6_16. ISBN 978-1-58829-399-2. PMID 16350956.
19. ^ Marquet P, Lachâtre G; Lachâtre (October 1999). "Liquid chromatography-mass spectrometry: potential in forensic and clinical toxicology". Journal of Chromatography B. 733 (1–2): 93–118. doi:10.1016/S0378-4347(99)00147-4. PMID 10572976.
20. ^ "Propedia v2.3 - Peptide-Protein Interactions Database". bioinfo.dcc.ufmg.br. Retrieved 2023-03-28.
21. ^ a b Martins, Pedro M.; Santos, Lucianna H.; Mariano, Diego; Queiroz, Felippe C.; Bastos, Luana L.; Gomes, Isabela de S.; Fischer, Pedro H. C.; Rocha, Rafael E. O.; Silveira, Sabrina A.; de Lima, Leonardo H. F.; de Magalhães, Mariana T. Q.; Oliveira, Maria G. A.; de Melo-Minardi, Raquel C. (December 2021). "Propedia: a database for protein–peptide identification based on a hybrid clustering algorithm". BMC Bioinformatics. 22 (1): 1. doi:10.1186/s12859-020-03881-z. ISSN 1471-2105. PMC 7776311. PMID 33388027.
22. ^ Neduva, Victor; Linding, Rune; Su-Angrand, Isabelle; Stark, Alexander; Masi, Federico de; Gibson, Toby J; Lewis, Joe; Serrano, Luis; Russell, Robert B (2005-11-15). Matthews, Rowena (ed.). "Systematic Discovery of New Recognition Peptides Mediating Protein Interaction Networks". PLOS Biology. 3 (12): e405. doi:10.1371/journal.pbio.0030405. ISSN 1545-7885. PMC 1283537. PMID 16279839.
23. ^ Tao, Kai; Makam, Pandeeswar; Aizen, Ruth; Gazit, Ehud (17 Nov 2017). "Self-assembling peptide semiconductors". Science. 358 (6365): eaam9756. doi:10.1126/science.aam9756. PMC 5712217. PMID 29146781.
24. ^ Tao, Kai; Levin, Aviad; Adler-Abramovich, Lihi; Gazit, Ehud (26 Apr 2016). "Fmoc-modified amino acids and short peptides: simple bio-inspired building blocks for the fabrication of functional materials". Chem. Soc. Rev. 45 (14): 3935–3953. doi:10.1039/C5CS00889A. PMID 27115033.
25. ^ Tao, Kai; Wang, Jiqian; Zhou, Peng; Wang, Chengdong; Xu, Hai; Zhao, Xiubo; Lu, Jian R. (February 10, 2011). "Self-Assembly of Short Aβ(16−22) Peptides: Effect of Terminal Capping and the Role of Electrostatic Interaction". Langmuir. 27 (6): 2723–2730. doi:10.1021/la1034273. PMID 21309606.
26. ^ Ian Hamley (2011). "Self-Assembly of Amphiphilic Peptides" (PDF). Soft Matter. 7 (9): 4122–4138. Bibcode:2011SMat....7.4122H. doi:10.1039/C0SM01218A.
27. ^ Kai Tao; Guy Jacoby; Luba Burlaka; Roy Beck; Ehud Gazit (July 26, 2016). "Design of Controllable Bio-Inspired Chiroptic Self-Assemblies". Biomacromolecules. 17 (9): 2937–2945. doi:10.1021/acs.biomac.6b00752. PMID 27461453.
28. ^ Kai Tao; Aviad Levin; Guy Jacoby; Roy Beck; Ehud Gazit (23 August 2016). "Entropic Phase Transitions with Stable Twisted Intermediates of Bio‐Inspired Self‐Assembly". Chem. Eur. J. 22 (43): 15237–15241. doi:10.1002/chem.201603882. PMID 27550381.
29. ^ Donghui Jia; Kai Tao; Jiqian Wang; Chengdong Wang; Xiubo Zhao; Mohammed Yaseen; Hai Xu; Guohe Que; John R. P. Webster; Jian R. Lu (June 16, 2011). "Dynamic Adsorption and Structure of Interfacial Bilayers Adsorbed from Lipopeptide Surfactants at the Hydrophilic Silicon/Water Interface: Effect of the Headgroup Length". Langmuir. 27 (14): 8798–8809. doi:10.1021/la105129m. PMID 21675796.
30. ^ Heitz, Marc; Javor, Sacha; Darbre, Tamis; Reymond, Jean-Louis (2019-08-21). "Stereoselective pH Responsive Peptide Dendrimers for siRNA Transfection". Bioconjugate Chemistry. 30 (8): 2165–2182. doi:10.1021/acs.bioconjchem.9b00403. ISSN 1043-1802. PMID 31398014. S2CID 199519310.
31. ^ Boelsma E, Kloek J; Kloek (March 2009). "Lactotripeptides and antihypertensive effects: a critical review". The British Journal of Nutrition. 101 (6): 776–86. doi:10.1017/S0007114508137722. PMID 19061526.
32. ^ Xu JY, Qin LQ, Wang PY, Li W, Chang C (October 2008). "Effect of milk tripeptides on blood pressure: a meta-analysis of randomized controlled trials". Nutrition. 24 (10): 933–40. doi:10.1016/j.nut.2008.04.004. PMID 18562172.
33. ^ Pripp AH (2008). "Effect of peptides derived from food proteins on blood pressure: a meta-analysis of randomized controlled trials". Food & Nutrition Research. 52: 10.3402/fnr.v52i0.1641. doi:10.3402/fnr.v52i0.1641. PMC 2596738. PMID 19109662.
34. ^ Engberink MF, Schouten EG, Kok FJ, van Mierlo LA, Brouwer IA, Geleijnse JM (February 2008). "Lactotripeptides show no effect on human blood pressure: results from a double-blind randomized controlled trial". Hypertension. 51 (2): 399–405. doi:10.1161/HYPERTENSIONAHA.107.098988. PMID 18086944.
35. ^ Wu, Hongzhong; Ren, Chunyan; Yang, Fang; Qin, Yufeng; Zhang, Yuanxing; Liu, Jianwen (April 2016). "Extraction and identification of collagen-derived peptides with hematopoietic activity from Colla Corii Asini". Journal of Ethnopharmacology. 182: 129–136. doi:10.1016/j.jep.2016.02.019. PMID 26911525.

* v
* t
* e

Hormones

Endocrine
glands|

| Hypothalamic–
pituitary|

| Hypothalamus|

* GnRH
* TRH
* Dopamine
* CRH
* GHRH
* Somatostatin (GHIH)
* MCH

|

Posterior pituitary|

* Oxytocin
* Vasopressin

Anterior pituitary|

* FSH
* LH
* TSH
* Prolactin
* POMC
* CLIP
* ACTH
* MSH
* Endorphins
* Lipotropin
* GH

Adrenal axis|

* Adrenal cortex
* Aldosterone
* Cortisol
* Cortisone
* DHEA
* DHEA-S
* Androstenedione
* Adrenal medulla
* Adrenaline
* Norepinephrine

Thyroid|

* Thyroid hormones
* T3
* T4
* Calcitonin
* Thyroid axis

Parathyroid|

* PTH

Gonadal axis|

| Testis|

* Testosterone
* AMH
* Inhibin

|

Ovary|

* Estradiol
* Progesterone
* Activin
* Inhibin
* Relaxin
* GnSAF

Placenta|

* hCG
* HPL
* Estrogen
* Progesterone

Pancreas|

* Glucagon
* Insulin
* Amylin
* Somatostatin
* Pancreatic polypeptide

Pineal gland|

* Melatonin
* N,N-Dimethyltryptamine
* 5-Methoxy-N,N-dimethyltryptamine

Other|

| Thymus|

* Thymosins
* Thymosin α1
* Beta thymosins
* Thymopoietin
* Thymulin

|

Digestive system|

| Stomach|

* Gastrin
* Ghrelin

|

Duodenum|

* CCK
* GIP
* Secretin
* Motilin
* VIP

Ileum|

* Enteroglucagon
* Peptide YY
* GLP-1

Liver/other|

* Insulin-like growth factor
* IGF-1
* IGF-2

Adipose tissue|

* Leptin
* Adiponectin
* Resistin

Skeleton|

* Osteocalcin

Kidney|

* Renin
* EPO
* Calcitriol
* Prostaglandin

Heart|

* Natriuretic peptide
* ANP
* BNP

* v
* t
* e

Encoded (proteinogenic) amino acids

General topics|

* Protein
* Peptide
* Genetic code

By properties|

| Aliphatic|

* Branched-chain amino acids (Valine
* Isoleucine
* Leucine)
* Methionine
* Alanine
* Proline
* Glycine

|

Aromatic|

* Histidine
* Tyrosine
* Tryptophan
* Phenylalanine

Polar, uncharged|

* Asparagine
* Glutamine
* Serine
* Threonine

Positive charge (pKa)|

* Lysine (≈10.8)
* Arginine (≈12.5)
* Histidine (≈6.1)
* Pyrrolysine

Negative charge (pKa)|

* Aspartic acid (≈3.9)
* Glutamic acid (≈4.1)
* Selenocysteine (≈5.4)
* Cysteine (≈8.3)
* Tyrosine (≈10.1)

* Amino acids types: Encoded (proteins)
* Essential
* Non-proteinogenic
* Ketogenic
* Glucogenic
* Secondary amino
* Imino acids
* D-amino acids
* Dehydroamino acids

* v
* t
* e

Protein primary structure and posttranslational modifications

General|

* Peptide bond
* Protein biosynthesis
* Proteolysis
* Racemization
* N–O acyl shift

N terminus|

* Acetylation
* Carbamylation
* Formylation
* Glycation
* Methylation
* Myristoylation (Gly)

C terminus|

* Amidation
* Glycosyl phosphatidylinositol (GPI)
* O-methylation
* Detyrosination

Single specific AAs|

| Serine/Threonine|

* Phosphorylation
* Dephosphorylation
* Glycosylation
* O-GlcNAc
* ADP-ribosylation

|

Tyrosine|

* Phosphorylation
* Dephosphorylation
* ADP-ribosylation
* Sulfation
* Porphyrin ring linkage
* Adenylylation
* Flavin linkage
* Topaquinone (TPQ) formation
* Detyrosination

Cysteine|

* Palmitoylation
* Prenylation

Aspartate|

* Succinimide formation
* ADP-ribosylation

Glutamate|

* Carboxylation
* ADP-ribosylation
* Methylation
* Polyglutamylation
* Polyglycylation

Asparagine|

* Deamidation
* Glycosylation

Glutamine|

* Transglutamination

Lysine|

* Methylation
* Acetylation
* Acylation
* Adenylylation
* Hydroxylation
* Ubiquitination
* Sumoylation
* ADP-ribosylation
* Deamination
* Oxidative deamination to aldehyde
* O-glycosylation
* Imine formation
* Glycation
* Carbamylation
* Succinylation
* Lactylation
* Propionylation
* Butyrylation

Arginine|

* Citrullination
* Methylation
* ADP-ribosylation

Proline|

* Hydroxylation

Histidine|

* Diphthamide formation
* Adenylylation

Tryptophan|

* C-mannosylation

Crosslinks between two AAs|

| Cysteine–Cysteine|

* Disulfide bond
* ADP-ribosylation

|

Methionine–Hydroxylysine|

* Sulfilimine bond

Lysine–Tyrosine|

* Lysine tyrosylquinone (LTQ) formation

Tryptophan–Tryptophan|

* Tryptophan tryptophylquinone (TTQ) formation

Crosslinks between three AAs|

| Serine–Tyrosine–Glycine|

* p-Hydroxybenzylidene-imidazolinone (HBI) formation (chromophore)

|

Histidine–Tyrosine–Glycine|

* 4-(p-hydroxybenzylidene)-5-imidazolinone (HBI) formation (chromophore)

Alanine–Serine–Glycine|

* Methylidene-imidazolone (MIO) formation

Crosslinks between four AAs|

| Allysine–Allysine–Allysine–Lysine|

* Desmosine

|

* v
* t
* e

Metabolism: Protein metabolism, synthesis and catabolism enzymes

Essential amino acids are in Capitals

K→acetyl-CoA|

| LYSINE→|

* Saccharopine dehydrogenase
* Glutaryl-CoA dehydrogenase

|

LEUCINE→|

* 3-Hydroxybutyryl-CoA dehydrogenase
* Branched-chain amino acid aminotransferase
* Branched-chain alpha-keto acid dehydrogenase complex
* Enoyl-CoA hydratase
* HMG-CoA lyase
* HMG-CoA reductase
* Isovaleryl coenzyme A dehydrogenase
* α-Ketoisocaproate dioxygenase
* Leucine 2,3-aminomutase
* Methylcrotonyl-CoA carboxylase
* Methylglutaconyl-CoA hydratase

(See Template:Leucine metabolism in humans – this diagram does not include the pathway for β-leucine synthesis via leucine 2,3-aminomutase)

TRYPTOPHAN→|

* Indoleamine 2,3-dioxygenase/Tryptophan 2,3-dioxygenase
* Arylformamidase
* Kynureninase
* 3-hydroxyanthranilate oxidase
* Aminocarboxymuconate-semialdehyde decarboxylase
* Aminomuconate-semialdehyde dehydrogenase

PHENYLALANINE→tyrosine→|

* (see below)

| G→pyruvate
→citrate|

| glycine→serine→|

* Serine hydroxymethyltransferase
* Serine dehydratase

* glycine→creatine: Guanidinoacetate N-methyltransferase
* Creatine kinase

|

alanine→|

* Alanine transaminase

cysteine→|

* D-cysteine desulfhydrase

threonine→|

* L-threonine dehydrogenase

G→glutamate→
α-ketoglutarate|

| HISTIDINE→|

* Histidine ammonia-lyase
* Urocanate hydratase
* Formiminotransferase cyclodeaminase

|

proline→|

* Proline oxidase
* Pyrroline-5-carboxylate reductase
* 1-Pyrroline-5-carboxylate dehydrogenase/ALDH4A1
* PYCR1

arginine→|

* Ornithine aminotransferase
* Ornithine decarboxylase
* Agmatinase

→alpha-ketoglutarate→TCA|

* Glutamate dehydrogenase

Other|

* cysteine+glutamate→glutathione: Gamma-glutamylcysteine synthetase
* Glutathione synthetase
* Gamma-glutamyl transpeptidase

* glutamate→glutamine: Glutamine synthetase
* Glutaminase

G→propionyl-CoA→
succinyl-CoA|

| VALINE→|

* Branched-chain amino acid aminotransferase
* Branched-chain alpha-keto acid dehydrogenase complex
* Enoyl-CoA hydratase
* 3-hydroxyisobutyryl-CoA hydrolase
* 3-hydroxyisobutyrate dehydrogenase
* Methylmalonate semialdehyde dehydrogenase

|

ISOLEUCINE→|

* Branched-chain amino acid aminotransferase
* Branched-chain alpha-keto acid dehydrogenase complex
* 3-hydroxy-2-methylbutyryl-CoA dehydrogenase

METHIONINE→|

* generation of homocysteine: Methionine adenosyltransferase
* Adenosylhomocysteinase

* regeneration of methionine: Methionine synthase/Homocysteine methyltransferase
* Betaine-homocysteine methyltransferase

* conversion to cysteine: Cystathionine beta synthase
* Cystathionine gamma-lyase

THREONINE→|

* Threonine aldolase

→succinyl-CoA→TCA|

* Propionyl-CoA carboxylase
* Methylmalonyl CoA epimerase
* Methylmalonyl-CoA mutase

G→fumarate|

| PHENYLALANINE→tyrosine→|

* Phenylalanine hydroxylase
* Tyrosine aminotransferase
* 4-Hydroxyphenylpyruvate dioxygenase
* Homogentisate 1,2-dioxygenase
* Fumarylacetoacetate hydrolase

* tyrosine→melanin: Tyrosinase

|

G→oxaloacetate|

| asparagine→aspartate→|

* Asparaginase/Asparagine synthetase
* Aspartate transaminase

|

Authority control databases: National |

* Germany
* United States
* France
* BnF data
* Japan
* Czech Republic
* Israel

|

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