Need GTPase for positive control

Dima Klenchin klenchin at
Tue Aug 22 14:31:21 EST 1995

>AFAIK transducin is different from other G proteins in 
that it has
>no GTPase activity when unstimulated. So you have to 
>the rods to get transducin activity (BTW a nice control).

That's correct... and incorrect. Transducin sticks to
bleached rhodopsin and stays there practically irreversibly 
in the absence of GTP. So a lot of crap could be stripped 
off membranes, allowing for >80% pure G(t) elution by GTP. 
So, for the GTPase assay one can purify 100% bleached 
membranes and start reaction by GTP addition. 

Regards. -Dima

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