Re: Hydrophobicity of residues

Jens J Loesel (
Thu, 1 Feb 1996 09:07:56 +0000

Two nice questions, and the first two answers were interesting
to read. But befor I give my answer (opinion) I have to question
the origional "seemingly simple question".

First: what does hydrophobic really mean ??

Does it mean for example:

What is the equilibrium concentration of my amino-acid in

For a hydrophobic amino acid this should be fairly small,
for a hydrophil amino acid this should big (whatever this
means in absolute numbers).

Doing so I have to ask the next question:

Do I measure my concentration in g/l or in mol/l.

Or do even I divide this number trough the number of non-hydrogen
side-chain atoms to get a relative measure of the hydrophobic
nature of the side-chain I could compare?.

For the hydrophobic amino acid I already have seen
Leucin and Isoleucin as answers. What is with Phenylalanine?

It was NOT under hudrophobic side chains, but under aromatic

I suppose, each aromatic carbon atom is less hydrophobic, as
the carbon atoms (sorry, just a guess) in Leucin and Isoleucin.
But it has more !!! of them (7 instead of just 4). This should
give an advantage in the total hydrophobic nature (if you measure
in mol/l).

For the less hydrophobic amino acids I have seen
Asparagine as an answer.

Here the question is, at which pH do I measure the hydrophobic

pH 7 (neutral), acidic or basic environment, ??

If Asparagine or Aspartic acid is more hydrophil should be
strongly related with the pH. pH also is important for all
other amino acids, but for aspartate/asparagine and
glutamate/glutamine it should have the biggest effect.

So my answers are:

1) Phenylalanine

2) Aspartic Acid

I would like to know why you think, my answer isn't right
(great if everyone thinks I'm right, but if not, could we
find an environment, where it is right).