I agree this 3:1, 4:1, ... 10:1 etc is a good approach - especially for
screening - as it samples more concentration conditions than the plain vanilla
1:1 set-up. One generally good thing too is that the precipitant also starts at
lower concentration - so less chance of setting up a load of trials and
watching them immediately crash out (although obviously not a problem in this
particular case!) .
I think the reason for differences from pre-prepared concentrated protein are
often to do with other components that come in with the protein - so anything
in the protein solution like buffer, salt, reductant, detergent, metal ions,
etc will be concentrated up alongside the protein.
cheers
Martyn
Martyn Symmons, MBU Cambridge.
As an aside I heard that the 1:1 derives from the days when pipettes could not
be trusted with such small volumes. The 1:1 ratio is the best chance to get a
droplet with reproducible relative concentrations regardless of any systematic
error in the exact volumes dispensed.
________________________________
From: Jacob Keller <[email protected]>
To: [email protected]
Sent: Friday, 5 March, 2010 17:02:15
Subject: Re: [ccp4bb] crystallization of a macromolecular complex
20 g/L is the same as 20 mg/ml, isn't it? That does
> not seem particularly high to me.
>
>Why not try 200 g/L?
>
As a variant to
this, you could just try doing 10:1 prot:ppt drops, and allowing the protein
concentration to increase in situ. In my limited experience, however, this is
not the same as setting up drops 1:1 with more concentrated protein, for
reasons
unknown to me. I wonder whether that is the experience of others on the BB as
well?
JPK
