Need GTPase for positive control

[Dima Klenchin]

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

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