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The hydropathy index of an amino acid is a number representing the hydrophobic or hydrophilic properties of its side-chain. It was proposed in 1982 by Jack Kyte and Russell F. Doolittle.[1]
The larger the number is, the more hydrophobic the amino acid. The most hydrophobic amino acids are isoleucine (4.5) and valine (4.2). The most hydrophilic ones are arginine (-4.5) and lysine (-3.9). This is very important in protein structure; hydrophobic amino acids tend to be internal (with regard to the protein's 3 dimensional shape) while hydrophilic amino acids are more commonly found towards the protein surface.
Hydropathy Index for the twenty natural amino acids (Kyte and Doolittle)
| A |
R |
N |
D |
C |
Q |
E |
G |
H |
I |
L |
K |
M |
F |
P |
S |
T |
W |
Y |
V |
| 1.8 |
-4.5 |
-3.5 |
-3.5 |
2.5 |
-3.5 |
-3.5 |
-0.4 |
-3.2 |
4.5 |
3.8 |
-3.9 |
1.9 |
2.8 |
-1.6 |
-0.8 |
-0.7 |
-0.9 |
-1.3 |
4.2 |
Amino acids sorted by increasing hydropathy index (based on previous table)
| R |
K |
N |
D |
Q |
E |
H |
P |
Y |
W |
S |
T |
G |
A |
M |
C |
F |
L |
V |
I |
| -4.5 |
-3.9 |
-3.5 |
-3.5 |
-3.5 |
-3.5 |
-3.2 |
-1.6 |
-1.3 |
-0.9 |
-0.8 |
-0.7 |
-0.4 |
1.8 |
1.9 |
2.5 |
2.8 |
3.8 |
4.2 |
4.5 |
[edit] References
