From owner-metabolic-reg@net.bio.net Sun Oct 15 23:00:00 1995 Path: biosci!bcm.tmc.edu!cs.utexas.edu!howland.reston.ans.net!tank.news.pipex.net!pipex!uknet!yama.mcc.ac.uk!io.salford.ac.uk!aber!innews From: prm@aber.ac.uk (Pedro Mendes) Newsgroups: bionet.metabolic-reg Subject: Re: Some idle speculation Date: 16 Oct 1995 10:51:47 GMT Organization: University of Wales Aberystwyth Lines: 46 Message-ID: <45tdg3$djo@fileserv.aber.ac.uk> References: NNTP-Posting-Host: pcfchb.dbs.aber.ac.uk X-Disclaimer: Warning - Sender not verifiable X-Newsreader: WinVN 0.99.6 NT In article , cam@rschp1.anu.edu.au says... > >The water content of mitchondria is very low, less than that of a protein >crystal apparently, on the order of 20% (or have I got the number wrong) >Anyway assuming that the water content of the cytosol is similarly very >low, In eukaryotic "cytosol" it is not as low as in mitos. However in prokaryotes the protein concentration is aproximatly the same as in eukaryotic mitochondria (if not larger) > that would seem to imply that serious protein protein interactions >would be required just to keep metabolites in moving through the various >pathways. There is interesting evidence that suggests the "cytosol" (I prefer cytosolic compartment...) to behave as a gel towards macromolecules but to behave as a dilute aqueous medium towards small molecular weight compounds. If this is right, then it is only proteins, mRNA, etc. that have slow diffusion, while most metabolites would diffuse like in water. > That in fact metabolites would _have_ to be shuttled directly >from enzyme to enzyme or run the risk of getting stuck into the gel of >the cytosol somewhere. If the evidence I cite above is right then this would not be so in most cases. In my opinion channelling is probably more important in i) enhancing the rate of coupled reactions by limiting the degrees of freedom of the substrate when binding to the second enzyme, ii) making metabolites not available for competing reactions, and iii) preventing some metabolites from escaping the cell (indole is a good example). >Anyway, just lead me to wondering which way things were leaning in the >metabolite shuttling debate. Certainly a subject worth debating, and >this seems a god place to do it. It is indeed, and I am willing to defend some of the statements I made above if there is interest in this topic here. -- Pedro Mendes Inst. Biological Sciences prm@aber.ac.uk (home: pedro@enzyme.demon.co.uk) Univ. Wales, Aberystwyth, http://gepasi.dbs.aber.ac.uk/pedro/prmhome.htm Dyfed SY23 3DA, U.K. PGP mail welcome! (public key on demand) FAX: +44 (0)1970 622350 .