Chromatography - Amino Acid Features

Amino acid

characteristic

structure

Alanine

Ala

A

Type: Hydrophobic

Arginine

Arg

R

Type: Alkaline
Function: The arginine side chain has three tightly bound nitrogen atoms and is a very basic amino acid with a pH of up to 12.5.
Arginine forms an electrostatic complex (salt bridge) with aspartic acid or glutamic acid to enhance the tertiary structure of the protein.
It also interacts with acidic groups attached to proteins, such as the phosphate groups of nucleic acids.

Asparagine

Asn

N

Type: weak polarity
Function: Asparagine is the main site of deamidation and the binding point of glycine (oligosaccharide).

Aspartic acid

Asp

D

Type: Acidic

Function: Aspartic acid has a pH of 4 and interacts with basic amino acids to form an electrostatic complex (salt bridge).
Aspartic acid is also a binding site for positively charged groups such as metal ions, and its function is important in a variety of proteins.

Cysteine

Cys

C

Type: weak polarity (sulphur)

Function: Cysteine ​​plays an important role in the tertiary structure of proteins, which react with other cysteine ​​side chains and form covalent bonds (disulfide bonds) in different parts of the polypeptide chain.

Glutamine

Gln

Q

Type: weak polarity

Function: Deamidation of glutamine is more difficult than asparagine, so it is not used as a deamidation site.

Glutamate

Glu

E

Type: Acidic

Function: The pH of glutamic acid is slightly higher than 4, and interacts with basic amino acids to form an electrostatic complex (salt bridge).
Glutamate is also a binding site for positively charged groups such as metal ions, and its function is important in various proteins.

Glycine

Gly

G

Type: Neutral
Function: Glycine is very small, only one hydrogen in the side chain, which acts as a neutral amino acid in the peptide chain.

Histidine

His

H

Type: Alkaline
Function: The histidine side chain is weakly alkaline and the pH is between 6 and 7. Histidine can bind to acids, but depends on the ambient pH.

Isoleucine

Ile

I

Type: Hydrophobic
Function: Like other hydrophobic amino acids, an isoleucine residue assists in the formation and maintenance of the tertiary structure of the protein.

Leucine

Leu

L

Type: Hydrophobic
Function: Like other hydrophobic amino acids, leucine assists in the formation and maintenance of the tertiary structure of the protein.

Lysine

Lys

K

Type: Alkaline
Function: The lysine side chain is a primary amine with a pH of ~10.5.
Lysine forms an electrostatic complex (salt bridge) with aspartic acid or glutamic acid to enhance the tertiary structure of the protein.
It also interacts with acidic groups attached to proteins, such as the phosphate groups of nucleic acids.

Methionine

Met

M

Type: weakly hydrophobic (sulphur-containing)

Function: Methionine is the most likely amino acid to be oxidized. It is an indicator of oxidation. Oxidation of methionine may also affect biological activity.

Phenylalanine

Phe

F

Type: hydrophobic, aromatic
Function: Like other hydrophobic amino acids, phenylalanine assists in the formation and maintenance of the tertiary structure of the protein.
Due to its aromatic nature, phenylalanine is also an effective detection target for UV absorption.

Proline

Pro

P

Type: weakly hydrophobic
Function: Proline is a unique amino acid with a hydrophobic side chain attached to the amino acid terminus that creates tension in the peptide chain and bends the peptide chain.
This structural feature assists in the formation of a tertiary structure of the protein.

Serine

Ser

S

Type: Polar (including hydroxyl)
Function: Serine binds to other amino acid residues or parts of proteins by hydrogen bonding. It can also bind to other proteins or groups through hydrogen bonding.
Serine is also the site of cellular protein phosphorylation.

Threonine

Thr

T

Type: Polar (including hydroxyl)

Function: Threonine binds to other amino acid residues or parts of proteins by hydrogen bonding. It can also bind to other proteins or groups through hydrogen bonding.
Threonine is also a site for cellular protein phosphorylation.

Tyrosine

Tyr

Y

Type: Polar (including hydroxyl), aromatic

Function: Tyrosine binds to other amino acid residues or parts of proteins by hydrogen bonding. It can also bind to other proteins or groups through hydrogen bonding.
Tyrosine is also the site of cellular protein phosphorylation. Tyrosine is aromatic and provides an ultraviolet absorption site.

Tryptophan

Trp

W

Type: hydrophobic, aromatic
Function: Tryptophan has a polycyclic structure and can be extended by hydrogen bonding. Due to its aromatic nature, tryptophan provides an ultraviolet light absorption site.
Tryptophan also emits a weak natural fluorescence.

Proline

Val

V

Type: Hydrophobic
Function: The proline side chain is a hydrophobic isopropyl group.
Like other hydrophobic amino acids, proline assists in the formation and maintenance of the tertiary structure of the protein.