[TML] Alien ecologies

[shadow at shadowgard.com]

On 29 Aug 2008 at 19:25, Jerry W Barrington wrote:

> On 8/29/08 3:56 PM, "Bruce Johnson" <johnson at pharmacy.arizona.edu> wrote:
> 
> > That's because the absorbtion peak does not depend on the protein
> > (which can change via evolution) but the captive metal atoms chemistry
> > (which cannot)
> 
> Hmm.  Chlorophyll a, b, c1, c2, and d all have Mg at the center.  Yet they
> have different peaks.  So apparently the proteins *do* matter.

The metals have several possible valences. In fact, that's part of 
what lets them do what they do.

Yeah, the surrounding atoms in the molecule shift peaks *slightly*.
 
> And: "Chlorophyll is a chlorin pigment, which is structurally similar to and
> produced through the same metabolic pathway as other porphyrin pigments such
> as heme."  Heme contains iron instead of magnesium.  Since they are both
> produced by the same pathway, it appears evolution *can* change what metal
> is in there.

He didn't say they couldn't change what metal was there. He said that 
evolution can't change the chemical properties of the metal. 

> Further, related molecules use cobalt, nickel, or even no
> metal.

Yeah, but for each metal (or non-metal) used, there's a very narrow 
range of properties you'll get.

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com