Why is solubility phe > tyr ?

T. Chyau Liang tliang at utmmg.med.uth.tmc.edu
Fri Jun 7 07:31:15 EST 1996


Solubility is determined by the equilibrium between the solid form and the
solvated form of the molecule.  The phenol group of Tyr apparently
"aggregates" better, i.e., the solid form of Tyr is more favored than the
solvated form when compared to Phe. In short, it is not because Phe is
more hydrophilic than Tyr.

Another little known fact is that pure d- or l- amino acids have better
solubilities (also by significant factors) than the racemic d,l mixture.
Presumably,this is due to the same mechanism and not because the the d- or
l- form is more hydrophilic than the d,l mixture.

Hope this helps.

T. Chyau Liang
U.Texas-Houston



[snip]  
> Can anybody explain to me, why the p-OH group in tyrosine has such a strong=
>  effect on the =
> 
> solubility of the amino acid, nin effect decreasing it almost to 1/20 of ph=
> e.
> 
> Is this only valid for the free enzyme, or would this also be the case for =
> the amino acid =
> 
> side-chains in proteins?  Does this mean, phe-side-chains have a more hydro=
> philic =
> 
> character than tyr=B9s in proteins?



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