Entropy-Enthalpy Compensation

Athel Cornish-Bowden athel at ir2cbm.cnrs-mrs.fr
Wed May 6 09:50:01 EST 1998


Petr Kuzmic wrote:

>Athel Cornish-Bowden wrote:
>>
>> I should be interested to know what readers of this news group think about
>> entropy-enthalpy compensation,
>
>A name that springs to mind is that of Otto Exner, who has diligently
>debunked several myths of this sort as statistical artifacts.

You are right. His contribution was one of the most important. I have read
his papers on this (some of them, anyway) and have been very surprised that
the subject didn't die a natural death after he pointed out the problems.
Many myths die very hard, but in this case its not just cranks who keep
them alive but some quite respectable scientists. I'm not sure if I can lay
my hands on the Exner references, so it'll be nice if you can post them.
Although one of the relevant papers was in Coll. Czech. Chem. Comm., which,
with all due to respect to Petr, many of us don't read very assiduously,
another was in Nature, where there is less excuse (even if on an objective
basis Coll. Czech. Chem. Comm is a more solidly respectable journal than
Nature).

>I will
>try to dig out a few reviews he authored, which perhaps may be not as
>widely known as they deserve.  My former colleague Exner was
>particularly insterested in the "iso-kinetic relationship", which, by
>the way, in biochemistry almost always ends up pointing to about 310 K
>as being the 'magic temperature'.
>
>It transpires that, aside from faulty statistics, there is another
>reason why we should be suspicious about dS vs. dH plots for series of
>enzyme/substrate/etc data obtained in aqueous solutions.   At one time,
>I was looking at several sets of temperature-dependent kinetic data [a
>series of substrates for recombinant human cyclophilin] having the
>'magic' isokinetic temperature [310 K], so I read up on the phenomenon
>in physical chemistry journals.   To my surprise, I found at least one
>paper in J. Phys. Chem. [have to look up that reference] showing that
>the "iso-kinetic temperature" of 310 K is predicted solely from the
>properties of -water-.
>
My feeling is that determining a "compensation temperature" is just a
complicated and indirect way of calculating the average temperature at
which the different measurements were made, i.e. that it's not a property
of the proteins studied but a "property" of the experimenter!


Athel

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