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what is alive?

Mario Vaneechoutte Mario.Vaneechoutte at rug.ac.be
Mon Sep 16 11:12:23 EST 1996


> > Ed Rybicki wrote:
> > > For me, it's simple: a prion is not replicating; like fire, it is simply
> > > propagating a chemical reaction which varies according to its
> > > substrate; therefore, it is not alive.
> >
Mario Vaneechoutte wrote:
> > itself', prions are alive. It came as a surprise that something else
> > than  DNA-RNA could replicate on its own and by a completely different mechanism...
> > prions keep transforming normal proteins into prion proteins.

Ed Rybicki wrote:
> Yes...BUT by acting as a peculiar catalyst, NOT by replicating any
> other information than purely structural.  Think about it: is the
> action of a prion protein in transforming another "normal" protein
> into a prion protein, any different to an antibody forcing a peptide
> into a particular configuration in its binding site, or a catalyst
> (read: enzyme) binding to, and forcing conversion of, its substrate?
> In this case the binder and the bindee CAN be the same protein in
> terms of primary sequence, or closely related variants thereof;
> however, it merely makes for a special case of a broader phenomenon
> which is simply catalysis.  Which isn't life....

Indeed, the line between catalysis and life is difficult to draw, think
of beginning life: from which moment on can one speak of life instead of
catalysis alone? Or think of life itself: couldn't it simply be
considered as a complex catalytical process and nothing more?

However, an important difference with the enzymatic reaction or the
antibody-antigen interaction is that prion transformation is
exponential.
In the case of antibodies it is a one-to-one process. Also in the case
of enzymes, the active component = the enzyme, is not duplicated.

A lot to discuss, indeed.


Mario Vaneechoutte
Laboratory Bacteriology & Virology
Blok A, De Pintelaan 185
University Hospital Ghent
Belgium 9000 Ghent
Tel: +32 9 240 36 92
Fax: +32 9 240 36 59
E-mail: Mario.Vaneechoutte at rug.ac.be



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