Thread View: sci.chem
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Started by Louis Hom
Sat, 13 Apr 2002 20:26
Interesting Biochem Comment
Author: Louis Hom
Date: Sat, 13 Apr 2002 20:26
Date: Sat, 13 Apr 2002 20:26
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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@ocf.berkeley.edu http://www.ocf.berkeley.edu/~lhom/
Re: Interesting Biochem Comment
Author: Marvin Margoshes
Date: Sun, 14 Apr 2002 18:46
Date: Sun, 14 Apr 2002 18:46
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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@OCF.Berkeley.EDU> wrote in message news:a9a493$21st$1@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@ocf.berkeley.edu > http://www.ocf.berkeley.edu/~lhom/
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