Interesting Biochem Comment

Marvin Margoshes physchemnospam at telocity.com
Sun Apr 14 13:46:16 EST 2002


In the metalloenzymes I know most about, the metal isn't at the site where
the substrate or coenzyme binds.  In zinc enzymes, and maybe others, the
function of the metal is to stabilize the 3-D structure of the enzyme.

"Louis Hom" <lhom at OCF.Berkeley.EDU> wrote in message
news:a9a493$21st$1 at agate.berkeley.edu...
> I don't any real point to make, I just thought this was an interesting
> comment from the 11Apr02 issue of Nature (p.587):
>
> "The enzymes that catalyse such reactions in nature typically operate at
> kilohertz frequencies: many biological chemical reactions
> convert substrates to products at rates of roughly 1,000 per second.
> Almost half of these enzymes require metal ions to achieve their
> catalytic functions -- usually Mg, Ca, Mn, Fe, Co, Ni, Cu and Zn --
> typically embedded in a three-dimensional protein matrix that
> ensures tightly controlled alignment of the reactants to achieve the
> desired formation and release of the product molecule(s). Outside
> the protein milieu, these metals in their typical + 2 and + 3 oxidation
> states form complexes that exchange their ligands rapidly Q
> they are kinetically labile.
>
> These ions seem, therefore, to have been adopted by living organisms
> precisely because they can bind to substrates and release
> products on a timescale commensurate with biological requirements. Notably
> absent from the list are second- and third-row
> transition metals, such as Ru, Pd and Pt. Complexes containing these metal
> ions are important as industrial catalysts, but their rates
> of ligand exchange are much lower than those of their first-row
> counterparts. With a few exceptions, such as Mo and W, such
> elements have therefore not been selected for biological functions."
> --
>
____________________________________________________________________________
__
> Lou Hom >K'93
> lhom at ocf.berkeley.edu
> http://www.ocf.berkeley.edu/~lhom/





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