Question: most proteins (barring certain bacterial ones) are composed of
laevorotary amino-acids. The common explanation to that is that The first
self-replicating organisms used L-amino acids but life could
just as well have started with D-amino acids. However, I did remember
someone giving an alternative explanation, that L-AA have some sort of an
edge on D-AA, regarding structural stabilty.
A friend of mine helped, and dug up the following article, abstract provided:
> > The development of concepts of chiral discrimination.
> >
> > Mason SF
> > Chemistry Department, King's College, London, England.
> >
> > Chirality 1: 183-91 (1989)
> >
> > Abstract
> > Pasteur's conjecture (1860) that biomolecular homochirality arose
> > from a chiral natural force as yet inaccessible in the laboratory
> > was supplanted by Fischer's (1894) "key and lock" hypothesis of
> > stereoselection in enantiomer to diastereomer conversions, whether
> > in the laboratory or in living organisms. Elaborations of the "key
> > and lock" hypothesis by Haldane (1930) and Pauling (1948) have been
> > illustrated and supported with modification by X-ray diffraction
> > crystal structures of enzyme-substrate complexes over the past
> > quarter century. Two types of mechanism for the product
> > diastereoselectivity in the reactions of an enantiomer with an
> > achiral reagent, early proposed, have recent support: one proposes a
> > quasidiastereomeric structure for the enantiomer attacked in the
> > ground state, the other for the corresponding transition state of
> > the reaction. Approaches to the differential biological activity of
> > two enantiomers postulate either the complete binding of each isomer
> > to a chiral receptor site, resulting in diastereomeric complexes
> > with inequivalent bioactivities, or the differential binding of the
> > two isomers to a set of three sites, with which only one isomer is
> > sterically congruent. Biochemical homochirality, based on the chiral
> > stereoselectivity of both biosynthetic and metabolic reactions,
> > derives from the evolutionary pressure for a progressive enhancement
> > of the kinetic efficiency and economy of those reactions. Recently
> > Pasteur has been vindicated in part, and the problem of the original
> > prebiotic enantiomeric excess left outstanding by Fischer has been
> > solved. The unification of the electromagnetic with the weak
> > interaction provided a universal chiral natural force, the
> > electroweak interaction, which favours the chiral series selected
> > during the course of biochemical evolution, both the D-sugars and
> > the L-amino acids.
> >
I have yet to read the article (library will only open Sunday), but does
anyone of this list's readers have any working knowledge of the subject?
Iddo
Iddo Friedberg ("\''/").___..--''"`-._
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