Point mutation causes increase in catalytic activity

[Tony Johnson]

Hi all,

I have an interesting mutant in an enzyme from E. coli that causes an 
_increase_ in the catalytic rate.  The point mutation isn't in an area of 
the protein that, in my opinion, functions as a negative regulator of the 
catalytic activity.  Nor is it very close to the active site.  My question 
is: Can anyone think of another example where a single point mutation causes 
an increase in the catalytic rate?

Of a more philosophical nature, in evolution, why wouldn't an enzyme evolve 
to maximize its catalytic rate?  Especially from an organism that seems to 
be streamlined for efficiency (E. coli), doesn't an increase in catalytic 
activity of an essential enzyme translate into increased efficiency and 
survivability and, thus, fitness?  Or is my understanding of evolution a bit 
too simplistic?

Thanks in advance,
Tom

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