Why 3H-GTP in GTP-binding assay?

Dima Klenchin klenchin at facstaff.wisc.edu
Wed Jul 2 18:28:07 EST 1997

In article <5p90l3$lsl at falcon.le.ac.uk>, "Dr E. Buxbaum" <EB15 at le.ac.uk> wrote:
:klenchin at facstaff.REMOVE_TO_REPLY.wisc.edu (Dima Klenchin) wrote:
:>I am not sure why not 14C-GTP but probably due to even 
:>lower specific radioactivity and still lower counting efficiency. 
:The counting efficiency of 14C is usually around 80-90% (compared to 
:about 20% with 3H). The biggest problem with 14C is its price tag. The 
:reason for this is that 14C compounds can only be isolated from organisms 
:grown on a 14C carbon source. Tritium labeled compounds can be prepared 
:in many cases by exchanging 1H against 3H essentially by sealing your 
:compound with 3H water into an ampoule, keeping it warm for a week or so 
:and then separating it from the water. Note that this process is 
:reversible, one of the reasons why 3H compounds do not keep as well as 
:the half life of 3H would suggest.

I stand corrected - counting efficiency of 14C is indeed extremely high. 
It is VERY low specific radioactivity and high price that makes it 
unusable for G-protein research. 

- Dima

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