From owner-metabolic-reg@net.bio.net Thu Jun 06 23:00:00 1996 Path: biosci!bcm.tmc.edu!news.uth.tmc.edu!bmb155.med.uth.tmc.edu!user From: tliang@utmmg.med.uth.tmc.edu (T. Chyau Liang) Newsgroups: bionet.molbio.proteins,de.sci.biologie,de.sci.chemie,sci.bio.misc,sci.chem,bionet.metabolic-reg,bionet.molbio.methds-reagnts,bionet.biophysics Subject: Re: Why is solubility phe > tyr ? Date: Fri, 07 Jun 1996 13:31:15 +0100 Organization: U. Texas-Houston Lines: 32 Message-ID: References: <31B735A3.30D8@ibex.ca> NNTP-Posting-Host: bmb155.med.uth.tmc.edu Mime-Version: 1.0 Content-Type: text/plain;charset=US-ASCII Content-Transfer-Encoding: 7bit Xref: biosci bionet.molbio.proteins:8072 sci.bio.misc:3418 sci.chem:57970 bionet.metabolic-reg:761 bionet.molbio.methds-reagnts:45482 bionet.biophysics:2093 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? .