500
AMINO ACIDS, PEPTIDES AND PROTEINS
Table 13.1 Amino acids: structures and standard abbreviations
Amino acid
Structure
Abbreviations
R group
classification
pK a
CO 2 H NH 2 Side-chain
Alanine
CO 2 H
NH 2
Ala A
Alkyl
non-polar
2.34
9.69
Arginine
H 2 N
N
H
CO 2 H
NH 2
NH
Arg R
Guanidine
basic polar
2.17
9.04
12.48
Asparagine
H 2 N
CO 2 H
NH 2
O
Asn N
Amide
polar
2.01
8.8
Aspartic acid
HO 2 C
CO 2 H
NH 2
Asp D
Carboxylic acid
acidic polar
1.89
9.60
3.65
Cysteine
HS
CO 2 H
NH 2
Cys C
Thiol
polar
1.96
8.18
10.29
Glutamic acid
HO 2 C
CO 2 H
NH 2
Glu E
Carboxylic acid
acidic polar
2.19
9.67
4.25
Glutamine
CO 2 H
NH 2
H 2 N
O
Gln Q
Amide
polar
2.17
9.13
Glycine
CO 2 H
NH 2
Gly G
Hydrogen
non-polar
2.34
9.6
Histidine
CO 2 H
NH 2
N
NH
His
H
Imidazole
basic polar
1.8
9.17
6.00
Isoleucine
CO 2 H
NH 2
Ile
I
Alkyl
non-polar
2.35
9.68
Leucine
CO 2 H
NH 2
Leu L
Alkyl
non-polar
2.36
9.60
Lysine
CO 2 H
NH 2
H 2 N
Lys K
Amine
basic polar
2.18
8.95
10.52