On Sun, 15 Feb 2004 07:32:48 +0000 (UTC), tomhendricks474{at}cs.com
(TomHendricks474) wrote:

>Which came first heat or enzymes?
>
>"The number of reactant molecules containing sufficient energy to
>undergo reaction is increased by either heating the mixture or
>adding an enzyme catalyst. 
>Heat increases the rate of rection by increasing the energy content of the
>molecule, while the enzyme does so by lowering the activation energy required
>for the reaction to occur."  
>- Cell and Mole Bio, Karp.
>
>Which is more likely:
>Life began as chemicals reacting to a cyclic heat, then as
>that heat subsided, those protobionts that could adjust by using enzymes were
>selected  OR
>Life began as a single enzyme or enzymes that overcame activation
>energy.
>
>To me there is only one logical choice - knowing the history of
>the earth, how far back life's origin has been pushed (before 3.7 bya) and how
>hot and turbulent that early period was;
>plus the impossible odds of prebiotic chemical reactions requiring activation
>energy, ever being selected  over chemicals not 
>requiring activation energy = scenario one IMO.
>
>Comment?
>

No one doubts that heat speeds reactions.  Your question in the
subject line, though, depends on what you mean by "enzyme".  Clearly,
before there were complex organic macromolecules that could catalyze
organic reactions, there were organic molecules that formed
spontaneously.  Many  modern models of abiogenesis use inorganic
(clay) materials as catalysts.  These are not "enzymes" but the
reaction ratese are still catalytically controlled. 

Still, it is always true that reaction rates, catalyzed or not, are
thermally sensitive and that reaction rates increase dramatically with
temperature. The only drawback of thermal activation to modern
biochemistry is that one of the reactions that increases with
temperature is the denaturation of proteinacous enzyme! That results
in an "optimal temperature" for each enzyme.  Natural selection
generaly selects enzymes to match their temperature optima to the
highest temperature they normally encounter.
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