Theoretical pI's

[JG. Head]

Hi,
I'm in the process of expressing a protein with about 200 amino acids, 
and my cells are making something that looks like the right thing, but it 
would be nice to verify that.  I've just been reading a paper where 
somebody calculates the theoretical pI of his protein and then shows that 
his expression product moves as predicted in 2d electrophoresis.  
Unfortunately he doesn't explain how he works out the value accurately.  
Nobody here can tell me how to calculate a theoretical pI from an amino  
acid sequence except very roughly, so if anybody knows how, or could 
point me to a reference I would be very grateful,

Thanks a lot,

Jared

--
Jared Head     at the Department of Biochemistry, University of Bristol
jared.head at bristol.ac.uk