Re: Thermophiles, enzymes and origins
Mon, 01 Apr 1996 21:15:29

Gene Godbold wrote:

>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.
There is a May 9, 1995 New York Times story which says that the thermophiles
have DNA which appears rather ancient in the PAUP generated family trees
constructed from 2000 organisms.