Biology Reference
In-Depth Information
TABLE 6.3 Kyte-Doolittle Hydropathy Index Values
for the 20 Common Amino Acids [5] .
Amino acid
Hydropathy index
Isoleucine
4.5
Valine
4.2
Leucine
3.8
Phenylalanine
2.8
Cysteine
2.5
Methionine
1.9
Alanine
1.8
Glycine
0.4
Threonine
0.7
Tryptophan
0.9
Serine
0.8
Tyrosine
1.3
Proline
1.6
Histidine
3.2
Glutamic Acid
3.5
Glutamine
3.5
Aspartic Acid
3.5
Asparagine
3.5
Lysine
3.9
Arginine
4.5
literature. Table 6 .3 lists the amino acids and their Kyte-Doolittle Hydropathy Index
values from the most hydrophobic (isoleucine) to the most hydrophilic amino acid
(arginine).
It is obvious that the Kyte Doolittle Hydropathy Index values are for the most part
consistent with the first crude classification of the amino acids into polar and non-polar.
By Kyte Doolittle, most of the non-polar amino acids have a positive Index while most of
the polar amino acids have a negative Index. A wide variety of hydropathy value tables
have now been proposed, and all are empirical amalgamations of experimentally derived
values. Although all of the hydropathy methods have similar amino acid rankings, all
have slight variations in some of the relative amino acid placings. Their empirical
numbers also vary over different ranges than do the Kyte Doolittle Hydropathy Index
of
4.5 to
4.5.
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