>  schrieb im Newsbeitrag 
> news:1102542900.826553.261810{at}z14g2000cwz.googlegroups.com...
>> I've checked a few biochem texts and websites that confirm that one of
>> the critical steps in the pathway organisms use to make ATP and GTP
>> involves using a tetrahydrofolate (THF) derivative as a source of a
>> carbon.  But in plants and microorganisms that can make their own THF,
>> the starting precursor is GTP?!  Perhaps I'm missing something as this
>> looks like a biochemical perpetual motion machine...?
>>

>"MMu"  wrote in message 
>news:41bdcbd2$0$11868$3b214f66{at}usenet.univie.ac.at...
> Hmm.. I think you might have misinterpreted what you read.
>
> THF is critical in cell proliferation, metabilisation of odd-chain-fatty 
> acids and a few other things but I don't think it is a major player in the 
> energy metabolism. (TPP and TMP are however.. did you confuse those two 
> perhaps?)
>
> Where did you read what you quoted?
>

Thanks for the reply.  A more generic overview is here:
http://web.indstate.edu/thcme/mwking/nucleotide-metabolism.html
(the section on purine biosynthesis), or a mechanistic view here:
http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/misc/purine1.html
N10-formyl-THF is apparently the source of the formyl group (giving THF as 
product) in "ring building" in both this early step pathway and again in a 
later antepenultimate step towards IMP biosynthesis.  But my understanding 
of THF biosynthesis is that the purine GTP is explicitly used in pterin 
construction, which are essential THF precursors.  I'm embarrassed that I 
can't figure this out -- there ought to be a simple solution to this 
apparent paradox?

(traded up the top posting for a cross posting, tit-for-tat)

[moderator's note: This article crossposted from sci.bio.evolution;
if followups seem inappropriate I will not hesitate to ding them.
Note that evolution/creation arguments are not allowed in s.b.e.;
please adjust your posts accordingly. - JAH]
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