Yang-Seok Kim asked: "Vitamin B1 synthetic genes are scattered in E.coli
chromosome. However, I found, two of them are joined and bacame
bifunctional protein in plant. Does anybody know the benifit of
bifuntionallity in evolution or the reference papers about
bifuntionallity?"
As your question is more about function than about evolution you should
probably post it on btk-mca at net.bio.net. I don't think there's been
anything recently there on channelling, but if you look back through the
archives for postings with "channelling" in the title you may find
something.
If the two enzymes catalyse non-consecutive reactions it isn't easy to
think of advantages, but if they are consecutive then in principle
having a bifunctional protein allows direct transfer of the common
intermediate from one active site to another (i.e. channelling). In the
published literature you would find it useful to look up papers and
reviews by (among others) Paul Srere or Judit Ovadi... Judit has a
recent book (sorry, I can't find it at this moment so I can't quote the
title) published by R. G. Landes (1995). There is also a multi-author
book edited by Loranne Agius and Stanley Sherratt called "Channelling in
intermediary metabolism", published by Portland Press (1996).
Incidentally, this has been quite controversial. Not everyone agrees
that channelling occurs at all (look for papers by P. B. Chock or H.
Gutfreund if you want to read a negative view), and not everyone agrees
that if it occurs it has any particular importance (I have been fairly
sceptical on this score myself).
The sort of observation you describe is quite common, incidentally, i.e.
there are other cases of enzymes that are separate proteins in E. coli
but multifunctional proteins in other organisms.
Athel
Home page: http://ir2lcb.cnrs-mrs.fr/lcbpage/athel/home_page.html
(which won't work until our server is fixed. I don't know when that will
be)
