In <3ulr2a$al7 at mserv1.dl.ac.uk> osvaldo at pen.gulbenkian.pt (Osvaldo Brasao 384)
writes:
>>>Excepting those many enzyme reactions which are coupled with the breakdown of
>energy-donor molecules such as ATP, it is generally assumed that the energy
>necessary to initiate the catalytic process comes exclusively from the
>reactants.
I don't have any references for you but I do want to correct a misconception that
you seem to have. Unless I am mistaken (which is entirely possible), a reaction
which can be catalyzed is assumed to have a lower total energy after the reaction
than before it and the purpose of the catalyst is to reduce some intermediate
energy barrier that prevents the reaction from going forward. Therefore, the
catalyst (enzyme) is required to initate the reaction which goes forward because
the reactants move to a lower energy state. If they didn't move to a lower
energy state, it would take more than a catalyst to pull it off (it would take
the addition of energy).
>I would be most interested in learning of papers reporting a different
>relationship between reactivity and temperature - but only for enzymes
not
>bound to membranes in order to avoid fluidity effects.
>Could someone kindly send me references of such papers?
>
I don't have any specific references that I can put my hands on today,
but I can tell you that the relationship between catalytic ability and
temperature is a bell shaped curve. This is because the catalyst
changes shape with temperature and becomes a better or poorer catalyst.
At too high a temperature, the protein denatures and becomes worthless
as a catalyst. At too low a temperature, the active site does not get
presented to the reactants (presumably). I have read about fish that
completely change their enzyme mix in the winter and the new enzymes
produced have a temperature optimum that is much lower than the enzymes
they use in the summer (also regulatory enzymes appear to be more
affected by temperature than non-regulatory ones). I hope you find the
references you are looking for but I am not sure they'll help you.
