jopa at ac.dal.ca wrote:
: In article <1tbqrk$f4r at zippy.Telcom.Arizona.EDU>, droberts at joplin.biosci.arizona.edu (Doug Roberts) writes:
: > This reminds me of a discussion/argument that I had with a labmate
: > recently. She argued that the reason for always keeping proteins in the cold
: > was to prevent denaturation. I believe that it must be for some other reason,
: > perhaps to prevent microorganism growth, or to slow down the activity of
: > proteases that may be present in the sample. It seems to me that at room
: > temperature, most proteins will be stable against denaturation. (Most of the
: > melting curves I've seen are quite flat around this temp.) The other point
: > is that we grow up our yeast at 36C and their proteins seem to work just
: > fine
: I suspect that there is a case for both. However, the denaturation
: which may be occurring at room temp. may not be a simple folding-
: unfolding denaturation, it could be a slow chemical process, ie.
: some oxidation or auto-proteolytic or, as you mentioned, the
: presence of additional proteinases. I would say it a question
: of time...proteins which are ok in yeast at 36C may not be okay
: in pure or semipure solution at 21C, since the environment is
: so different.
: Certainly the presence of microorganisms is a definite concern, I have
: seen solutions go bad and it is definitely because something is growing
: in it.
: Jonathan Parrish
: Department of Biochemistry
: Dalhousie University
: Halifax, N.S., Canada
Plus, it is instructive to calculate what the physiological concentration
of proteins is in the cell - mM or higher. This must also contribute
to stability in vivo. And, all those protective mechanisms - proteinase
inhibitors, free radical moppers atc are all working away in vivo.
Finally, steady state concentration in vivo does not mean that the
proteins are stable, necessarily - they could be turning over at a
terrific rate - a mouse, for instance, has a new liver every day!
-which as an aside, destroys concepts of nationality. Within days or weeks of
moving to a new country, many of your high turnover proteins will
have been replaced with new proteins, made locally. Others, like
crystallins, will take years. Eventually, you will be 'nationalised'
biochemically, if not politically!
Just my bit for world peace and harmony!