Periodic Chart of Amino Acids

HistidineX

Abbreviations: His, H
Systematic name: 2-amino-3-(1H-imidazol-4-yl)propanoic acid
Year of discovery (source): 1896 (sturin)
Origin of the name: from Greek histos, meaning "tissue", because it was thought to be important to tissue function

Chemical structure:

Chemical formula: C₆H₉N₃O₂
Appearance: colourless crystals
Molecular mass: 155.16 g/mol
Melting point: 277°C (decomposes)
Solubility (in water at 25°C): 4.19 g/100g
Hydrophobicity index (by Fauchere and Pliska): 0.130
Density: 1.432 g/ml
Surface area: 195 A²
Volume: 153.2 A³
Isoelectric point: 7.59 (pK₁ = 1.82 (α−COOH), pK₂ = 6.00 (imidazole), pK₃ = 9.17 (α−NH₃⁺))
Optical properties: [α] = −38.5 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: bitter
Source of occurrence: hemoglobin (7%)
Daily requirement: 0.90 g (essential amino acid)

Additional notes:
Histidine is a weakly basic, polar amino acid that is essential for humans. The imidazole ring present in its side chain contains two nitrogen atoms. His (in combination with Cys, Ser or Thr) is often found in the active center of enzymes.

Aspartic acidX

Abbreviations: Asp, D
Systematic name: 2-aminobutanedioic acid
Year of discovery (source): 1827 (asparagus, pea)
Origin of the name: named after asparagine, because it was first isolated from it by hydrolysis

Chemical structure:

Chemical formula: C₄H₇NO₄
Appearance: colourless crystals
Molecular mass: 133.10 g/mol
Melting point: 270°C (decomposes)
Solubility (in water at 25°C): 0.78 g/100g
Hydrophobicity index (by Fauchere and Pliska): −0.770
Density: 1.660 g/ml
Surface area: 150 A²
Volume: 111.1 A³
Isoelectric point: 2.77 (pK₁ = 1.88 (α−COOH), pK₂ = 3.65 (β−COOH), pK₃ = 9.60 (α−NH₃⁺))
Optical properties: [α] = +5.0 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: bitter
Source of occurrence: barley globulin (10%)
Daily requirement: non-essential amino acid

Additional notes:
Aspartic acid is an acidic amino acid and endogenous for mammals. Discovered in asparagus, which helped give it its name.

ArginineX

Abbreviations: Arg, R
Systematic name: 2-amino-5-guanidinopentanoic acid
Year of discovery (source): 1886 (lupine seedlings)
Origin of the name: from the Greek word arginoeis, which meant "silver", isolated as the silver salt

Chemical structure:

Chemical formula: C₆H₁₄N₄O₂
Appearance: white crystals
Molecular mass: 174.20 g/mol
Melting point: 238°C (decomposes)
Solubility (in water at 25°C): 15.00 g/100g
Hydrophobicity index (by Fauchere and Pliska): −1.010
Density: 1.100 g/ml
Surface area: 225 A²
Volume: 173.4 A³
Isoelectric point: 10.76 (pK₁ = 2.17 (α−COOH), pK₂ = 9.04 (α−NH₃⁺), pK₃ = 12.84 (guanidino group))
Optical properties: [α] = +12.5 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: bitter
Source of occurrence: salmine (86%), histones (16%)
Daily requirement: 1.80 g (essential amino acid)

Additional notes:
Arginine is a strongly basic, semi-essential amino acid (the body can produce it, but often in insufficient amounts). Arg-containing peptides are highly polar and readily water-soluble.

PhenylalanineX

Abbreviations: Phe, F
Systematic name: 2-amino-3-phenylpropanoic acid
Year of discovery (source): 1879 (lupine seedlings)
Origin of the name: named by Erlenmeyer and Lipp in 1883 because it looks like alanine with a phenyl group

Chemical structure:

Chemical formula: C₉H₁₁NO₂
Appearance: colourless crystals
Molecular mass: 165.19 g/mol
Melting point: 284°C (decomposes)
Solubility (in water at 25°C): 2.97 g/100g
Hydrophobicity index (by Fauchere and Pliska): 1.790
Density: 1.290 g/ml
Surface area: 210 A²
Volume: 189.9 A³
Isoelectric point: 5.48 (pK₁ = 1.83 (α−COOH), pK₂ = 9.13 (α−NH₃⁺))
Optical properties: [α] = −34.5 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Molar absorption coefficient: ε = 220 M⁻¹cm⁻¹ at λ = 257 nm
Smell: none
Taste: bitter
Source of occurrence: serum albumin (8%), γ-globulin (5%)
Daily requirement: 1.10 g (essential amino acid)

Additional notes:
Phenylalanine is an exogenous, non-polar amino acid. Together with His, Tyr and Trp, it is one of the aromatic amino acids.

AlanineX

Abbreviations: Ala, A
Systematic name: 2-aminopropanoic acid
Year of discovery (source): 1888 (silk fibroin)
Origin of the name: Al - is a shortening of aldehyde. The infix -an was added to make it easier to pronounce, the German ending -in.

Chemical structure:

Chemical formula: C₃H₇NO₂
Appearance: white powder
Molecular mass: 89.09 g/mol
Melting point: 297°C (decomposes)
Solubility (in water at 25°C): 16.65 g/100g
Hydrophobicity index (by Fauchere and Pliska): 0.310
Density: 1.401 g/ml
Surface area: 115 A²
Volume: 88.6 A³
Isoelectric point: 6.01 (pK₁ = 2.34 (α−COOH), pK₂ = 9.69 (α−NH₃⁺))
Optical properties: [α] = +1.8 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: sweet
Source of occurrence: silk fibroin (30%)
Daily requirement: non-essential amino acid

Additional notes:
Alanine is the simplest optically active, endogenous amino acid and the second most common in proteins.

CysteineX

Abbreviations: Cys, C
Systematic name: 2-amino-3-sulfhydrylpropanoic acid
Year of discovery (source): 1884 (cystine reduction)
Origin of the name: had an earlier spelling of cystine. That comes from the Ancient Greek word for "bladder", kustis.

Chemical structure:

Chemical formula: C₃H₇NO₂S
Appearance: white crystals or powder
Molecular mass: 121.16 g/mol
Melting point: 220°C (decomposes)
Solubility (in water at 25°C): very good, 27.7 g/100g
Hydrophobicity index (by Fauchere and Pliska): 1.540
Density: 1.680 g/ml
Surface area: 135 A²
Volume: 108.5 A³
Isoelectric point: 5.02 (pK₁ = 1.71 (α−COOH), pK₂ = 8.18 (thiol), pK₃ = 10.28 (α−NH₃⁺))
Optical properties: [α] = −16.5 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: hydrogen sulphide-mercaptan odor
Taste: neutral
Source of occurrence: hair keratin (18%), wool (12%), feathers (8%)
Daily requirement: non-essential amino acid

Additional notes:
Cysteine is a rare amino acid, but extremely important for the structure of peptides and proteins. Endogenous Cys contains a thiol group in the side chain, which is easily oxidized to form a disulfide bond. Two cysteine molecules form one cystine molecule. If two Cys residues are present in a peptide, a cyclic peptide can be formed.

GlycineX

Abbreviations: Gly, G
Systematic name: 2-aminoethanoic acid
Year of discovery (source): 1820 (silk fibroin)
Origin of the name: from the Greek word glukus, meaning "sweet"(due to its sweet taste), originally isolated from gelatin

Chemical structure:

Chemical formula: C₂H₅NO₂
Appearance: White solid
Molecular mass: 75.07 g/mol
Melting point: 292°C (decomposes)
Solubility (in water at 25°C): 24.99 g/100g
Hydrophobicity index (by Fauchere and Pliska): 0.000
Density: 1.607 g/ml
Surface area: 75 A²
Volume: 60.1 A³
Isoelectric point: 5.97 (pK₁ = 2.34 (α−COOH), pK₂ = 9.60 (α−NH₃⁺))
Optical properties: optically inactive
Smell: none
Taste: sweet
Source of occurrence: silk fibroin (44%), gelatin (26%)
Daily requirement: non-essential amino acid

Additional notes:
Glycine is the simplest amino acid and one of the most frequently encountered in peptides or proteins. Gly is an endogenous, optically inactive amino acid.

GlutamineX

Abbreviations: Gln, Q
Systematic name: 2,5-diamino-5-oxopentanoic acid
Year of discovery (source): 1877 (beetroot juice)
Origin of the name: named before it was isolated, because it was hypothesized to be similar to glutamic acid

Chemical structure:

Chemical formula: C₅H₁₀N₂O₃
Appearance: white crystalline powder
Molecular mass: 146.15 g/mol
Melting point: 185°C (decomposes)
Solubility (in water at 25°C): 2.50 g/100g
Hydrophobicity index (by Fauchere and Pliska): −0.220
Density: 1.470 g/ml
Surface area: 180 A²
Volume: 143.8 A³
Isoelectric point: 5.65 (pK₁ = 2.17 (α−COOH), pK₂ = 9.13 (α−NH₃⁺))
Optical properties: [α] = +6.3 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: sweet
Source of occurrence: beetroot juice
Daily requirement: non-essential amino acid

Additional notes:
Glutamine is the amide derivative of glutamic acid. Free glutamine is found in large quantities in the human body. Gln present at the start of the peptide sequence forms pyroglutamic acid spontaneously or with the help of an enzyme.

Glutamic acidX

Abbreviations: Glu, E
Systematic name: 2-aminopentanedioic acid
Year of discovery (source): 1866 (wheat gluten)
Origin of the name: Glut - refers to how the compound was first isolated from gluten by chemist Karl Ritthausen

Chemical structure:

Chemical formula: C₅H₉NO₄
Appearance: white crystalline powder
Molecular mass: 147.13 g/mol
Melting point: 249°C (decomposes)
Solubility (in water at 25°C): 0.86 g/100g
Hydrophobicity index (by Fauchere and Pliska): −0.640
Density: 1.460 g/ml
Surface area: 190 A²
Volume: 138.4 A³
Isoelectric point: 3.24 (pK₁ = 2.17 (α−COOH), pK₂ = 4.32 (γ−COOH), pK₃ = 9.67 (α−NH₃⁺))
Optical properties: [α] = +12.6 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: tasty
Source of occurrence: cereal gliadin (38%), corn zein (23%)
Daily requirement: non-essential amino acid

Additional notes:
Glutamic acid is an acidic, endogenous amino acid. The sodium salt of glutamic acid (monosodium glutamate, MSG) is known as a taste-enhancer. Glu has great physiological importance in the nervous system as a neurotransmitter. Glu forms pyroglutamic acid much less readily than glutamine.

LysineX

Abbreviations: Lys, K
Systematic name: 2,6-diaminohexanoic acid
Year of discovery (source): 1886 (casein)
Origin of the name: named in 1889 from the Ancient Greek word lusis, meaning "loosening"

Chemical structure:

Chemical formula: C₆H₁₄N₂O₂
Appearance: colourless crystals
Molecular mass: 146.19 g/mol
Melting point: 224°C (decomposes)
Solubility (in water at 25°C): very good, about 150.00 g/100g
Hydrophobicity index (by Fauchere and Pliska): −0.990
Density: 1.125 g/ml
Surface area: 200 A²
Volume: 168.6 A³
Isoelectric point: 9.82 (pK₁ = 2.18 (α−COOH), pK₂ = 9.12 (α−NH₃⁺), pK₃ = 10.53 (ε−NH₃⁺))
Optical properties: [α] = +13.5 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: neutral
Source of occurrence: myoglobin (15%), serum albumin (13%)
Daily requirement: 0.80 g (essential amino acid)

Additional notes:
Lysine is a basic, exogenous amino acid, that carries a second amino group in its side chain (is an α,ε-diamino acid).

LeucineX

Abbreviations: Leu, L
Systematic name: 2-amino-4-methylpentanoic acid
Year of discovery (source): 1819 (cottage cheese)
Origin of the name: first used in 1826 by chemist William Henry. Comes from the Greek word leukos, "white".

Chemical structure:

Chemical formula: C₆H₁₃NO₂
Appearance: white powder
Molecular mass: 131.18 g/mol
Melting point: 337°C (decomposes)
Solubility (in water at 25°C): 2.43 g/100g
Hydrophobicity index (by Fauchere and Pliska): 1.700
Density: 1.191 g/ml
Surface area: 170 A²
Volume: 166.7 A³
Isoelectric point: 5.98 (pK₁ = 2.36 (α−COOH), pK₂ = 9.60 (α−NH₃⁺))
Optical properties: [α] = −11.0 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: bitter
Source of occurrence: corn zein (19%), serum albumin (13%)
Daily requirement: 1.10 g (essential amino acid)

Additional notes:
Leucine is non-polar molecule, essential for humans. The name leucine comes from the white (Greek: leukos) leaves in which it crystallizes.

MethionineX

Abbreviations: Met, M
Systematic name: 2-amino-4-(methylthio)butanoic acid
Year of discovery (source): 1921 (casein)
Origin of the name: coined in 1926 by Barger nad Coyne as a contraction of γ-methiol-α-aminobutyric acid.

Chemical structure:

Chemical formula: C₅H₁₁NO₂S
Appearance: White crystalline powder
Molecular mass: 149.21 g/mol
Melting point: 283°C (decomposes)
Solubility (in water at 25°C): very good, 3.38 g/100g
Hydrophobicity index (by Fauchere and Pliska): 1.230
Density: 1.340 g/ml
Surface area: 185 A²
Volume: 162.9 A³
Isoelectric point: 5.74 (pK₁ = 2.28 (α−COOH), pK₂ = 9.21 (α−NH₃⁺))
Optical properties: [α] = −9.8 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: hydrogen sulphide-mercaptan odor
Taste: tasty
Source of occurrence: ovalbumin (5%), γ-casein (4%)
Daily requirement: 1.10 g (essential amino acid)

Additional notes:
Methionibe is, like cysteine, a sulfur-containing amino acid. The sulfur is present as methyl thioether, as reflected in the name "Me-thio". Thioethers are sensitive to oxidation, which should be heeded when handling Met-containing peptides.

AsparagineX

Abbreviations: Asn, N
Systematic name: 2-amino-3-carbamoylpropanoic acid
Year of discovery (source): 1806 (asparagus)
Origin of the name: from a sample of asparagus juice, after which it was named

Chemical structure:

Chemical formula: C₄H₈N₂O₃
Appearance: white crystals
Molecular mass: 132.12 g/mol
Melting point: 236°C (decomposes)
Solubility (in water at 25°C): 3.53 g/100g
Hydrophobicity index (by Fauchere and Pliska): −0.600
Density: 1.540 g/ml
Surface area: 160 A²
Volume: 114.1 A³
Isoelectric point: 5.41 (pK₁ = 2.02 (α−COOH), pK₂ = 8.80 (α−NH₃⁺))
Optical properties: [α] = −5.6 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: neutral
Source of occurrence: asparagus juice
Daily requirement: non-essential amino acid

Additional notes:
Asparagine is the amide derivative of aspartic acid and like the latter, was discovered in asparagus. Asn is a polar amino acid and is relatively labile in peptides and proteins.

SerineX

Abbreviations: Ser, S
Systematic name: 2-amino-3-hydroxypropanoic acid
Year of discovery (source): 1865 (silk)
Origin of the name: from the Latin word sericum, meaning "silk", because it was first obtained from silk protein

Chemical structure:

Chemical formula: C₃H₇NO₂
Appearance: white crystals or powder
Molecular mass: 105.09 g/mol
Melting point: 228°C (decomposes)
Solubility (in water at 25°C): 5.02 g/100g
Hydrophobicity index (by Fauchere and Pliska): −0.040
Density: 1.537 g/ml
Surface area: 115 A²
Volume: 89.0 A³
Isoelectric point: 5.68 (pK₁ = 2.21 (α−COOH), pK₂ = 9.15 (α−NH₃⁺))
Optical properties: [α] = −7.5 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: sweet
Source of occurrence: trypsinogen (17%), silk fibroin (16%)
Daily requirement: non-essential amino acid

Additional notes:
Serine is a polar amino acid due to the hydroxyl group in the side chain. The name of this endogenous amino acid is derived from the Latin (sericum) for silk.

TyrosineX

Abbreviations: Tyr, Y
Systematic name: 2-amino-3-(4-hydroxyphenyl)propanoic acid
Year of discovery (source): 1846 (casein)
Origin of the name: from Greek tyros, meaning "cheese", because it was obtained from old cheese

Chemical structure:

Chemical formula: C₉H₁₁NO₃
Appearance: white solid
Molecular mass: 181.19 g/mol
Melting point: 344°C (decomposes)
Solubility (in water at 25°C): 0.05 g/100g
Hydrophobicity index (by Fauchere and Pliska): 0.960
Density: 1.456 g/ml
Surface area: 230 A²
Volume: 193.6 A³
Isoelectric point: 5.66 (pK₁ = 2.20 (α−COOH), pK₂ = 9.11 (α−NH₃⁺), pK₃ = 10.07 (hydroxyl group))
Optical properties: [α] = −10.0 (c = 5M HCl, at 25°C and λ = 589.3 nm)
Molar absorption coefficient: ε = 1480 M⁻¹cm⁻¹ at λ = 274 nm
Smell: none
Taste: bitter
Source of occurrence: silk fibroin (13%), papain (15%)
Daily requirement: non-essential amino acid

Additional notes:
Tyrosine is an endogenous amino acid, produced from phenylalanine. Despite the presence of an aromatic ring in the side chain, this relatively non-polar amino acid is classified as a polar amino acid due to the presence of a hydroxyl group in the phenyl ring.

ThreonineX

Abbreviations: Thr, T
Systematic name: 2-amino-3-hydroxybutanoic acid
Year of discovery (source): 1935 (fibrin)
Origin of the name: named in 1936 after threose, a four-carbon monosaccharide that it was thought to resemble

Chemical structure:

Chemical formula: C₄H₉NO₃
Appearance: white crystals or powder
Molecular mass: 119.12 g/mol
Melting point: 253°C (decomposes)
Solubility (in water at 25°C): 10.6 g/ml
Hydrophobicity index (by Fauchere and Pliska): 0.260
Density: 1.307 g/ml
Surface area: 140 A²
Volume: 116.1 A³
Isoelectric point: 6.16 (pK₁ = 2.71 (α−COOH), pK₂ = 9.62 (α−NH₃⁺>))
Optical properties: [α] = −28.5 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: sweet
Source of occurrence: avidin (10%), hair keratin (8%)
Daily requirement: 0.70 g (essential amino acid)

Additional notes:
Threonine, like serine, contains a hydroxyl group in the side chain, but is an exogenous amino acid. Thr, in common with isoleucine, contains a second asymmetric carbon atom, so other stereoisomers are possible (allo-Thr).

IsoleucineX

Abbreviations: Ile, I
Systematic name: 2-amino-3-methylpentanoic acid
Year of discovery (source): 1904 (white beet)
Origin of the name: named in 1904 by Felix Ehrlich who observed that it was similar but not identical to leucine

Chemical structure:

Chemical formula: C₆H₁₃NO₂
Appearance: white crystals or powder
Molecular mass: 131.18 g/mol
Melting point: 284°C (decomposes)
Solubility (in water at 25°C): 4.12 g/100g
Hydrophobicity index (by Fauchere and Pliska): 1.800
Density: 1.035 g/ml
Surface area: 175 A²
Volume: 166.7 A³
Isoelectric point: 6.02 (pK₁ = 2.36 (α−COOH), pK₂ = 9.68 (α−NH₃⁺))
Optical properties: [α] = +12.4 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: bitter
Source of occurrence: oat globulin (4%), serum albumin (3%)
Daily requirement: 0.70 g (essential amino acid)

Additional notes:
Isoleucine is isomer of leucine, that have the same molecular formula and the same molecular weight, but differ in their structure. Due to the presence of two chiral centers in the isoleucine molecule, further stereoisomers (allo-Ile) are possible.

TryptophanX

Abbreviations: Trp, W
Systematic name: 2-amino-3-(1H-indol-3-yl)propanoic acid
Year of discovery (source): 1901 (casein)
Origin of the name: traces to Greek roots tripsis, meaning "rubbing", and phainein, meaning "to show"

Chemical structure:

Chemical formula: C₁₁H₁₂N₂O₂
Appearance: colourless crystals
Molecular mass: 204.23 g/mol
Melting point: 282°C (decomposes)
Solubility (in water at 25°C): 1.14 g/100g
Hydrophobicity index (by Fauchere and Pliska): 2.250
Density: 1.340 g/ml
Surface area: 255 A²
Volume: 227.8 A³
Isoelectric point: 5.89 (pK₁ = 2.38 (α−COOH), pK₂ = 9.39 (α−NH₃⁺))
Optical properties: [α] = −33.7 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Molar absorption coefficient: ε = 5500 M⁻¹cm⁻¹ at λ = 280 nm
Smell: none
Taste: neutral
Source of occurrence: lysozyme - eggs (11%), α-lactalbumin (7%)
Daily requirement: 0.25 g (essential amino acid)

Additional notes:
Tryptophan is a non-polar, exogenous amino acid, an indole derivative. The free amino acid has an antidepressant effect and is a precursor of serotonin. Trp fluoresces in the UV range (308-350 nm).

ProlineX

Abbreviations: Pro, P
Systematic name: pyrrolidine-2-carboxylic acid
Year of discovery (source): 1901 (casein)
Origin of the name: name comes from pyrrolidine, one of its constituents

Chemical structure:

Chemical formula: C₅H₉NO₂
Appearance: transparent crystals
Molecular mass: 115.13 g/mol
Melting point: 222°C (decomposes)
Solubility (in water at 25°C): 162.3 g/100g
Hydrophobicity index (by Fauchere and Pliska): 0.720
Density: 1.350 g/ml
Surface area: 145 A²
Volume: 112.7 A³
Isoelectric point: 6.30 (pK₁ = 1.99 (α−COOH), pK₂ = 10.06 (α−NH₃⁺))
Optical properties: [α] = −86.2 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: sweet
Source of occurrence: gelatine (16%), casein (11%)
Daily requirement: non-essential amino acid

Additional notes:
Proline is the only cyclic proteinogenic amino acid, composed of a 5-atom ring containing a secondary α-amino group and an C^α atom. Due to its special structure, Pro has a huge influence on the spatial structure of peptides and proteins.

ValineX

Abbreviations: Val, V
Systematic name: 2-amino-3-methylbutanoic acid
Year of discovery (source): 1901 (pancreas)
Origin of the name: name comes from its structural similarity to valeric acid that occurs in the roots of the valerian plant

Chemical structure:

Chemical formula: C₅H₁₁NO₂
Appearance: white crystals or powder
Molecular mass: 117.15 g/mol
Melting point: 315°C (decomposes)
Solubility (in water at 25°C): 8.85 g/100g
Hydrophobicity index (by Fauchere and Pliska): 1.220
Density: 1.230 g/ml
Surface area: 155 A²
Volume: 140.0 A³
Isoelectric point: 5.96 (pK₁ = 2.32 (α−COOH), pK₂ = 9.62 (α−NH₃⁺))
Optical properties: [α] = +5.63 (c = 1−2 in water, at 25°C and λ = 589.3 nm)
Smell: none
Taste: bitter
Source of occurrence: elastin of the bovine aorta (18%)
Daily requirement: 0.80 g (essential amino acid)

Additional notes:
Valine is a non-polar, exogenous amino acid.