Thermophiles, enzymes and origins

Gene Godbold (
Mon, 1 Apr 96 14:45:46 EST

I have a question that I hope some of you may be able to help me with.
What is the evidence that thermophiles were the first organisms?

The lab next door to where I work studies catalytic mechanisms and
proficiency in enzymes. The latter term refers to the catalytic
efficiency of the enzyme (k-cat/K-M) divided by the uncatalyzed rate.
While the catalytic efficiency of enzymes varies over only 600-fold, the
catalytic proficiency can vary over *14* orders of magnitude. Anyway, the
point of this is that certain reactions essential for life have
uncatalyzed rates with half-lives that are greater than 50 million years.
Any enzyme that catalyzes them has to be darn near perfect from the get-go
or nothing happens. But one of these reactions has a very high dependence
on temperature, so that, at 120 degrees (C), the half life is only 3 years
or so. It is therefore argued that the first organisms must have been
thermophiles. I'm willing to buy this, but I suspect that a lot of weird,
non-productive reactions might happen in an abiogenesis situation at
upwards of 100 degrees. I submit this to your collected knowledge. Thank
you in advance.

Gene Godbold
Dept. of Biochem. and Biophysics
UNC-Chapel Hill