Two questions: Absolute EtOH and Carboxypeptidase Digestion

Jeffery Haines jhaines at
Sun May 27 14:42:35 EST 2001

Hi, I know this is a molbio board, but I'm going to post my chem 
question anyways since I know there are a lot of helpful people on this board.

I recently performed an experiment involving the determination if an 
equilibrium constant in two solvent systems:  (1) absolute ethanol and 
(2) water    I am writing up my report, and I'm trying to compile a list 
of errors that may have caused a deviation from the experimental value.   
The reaction mixtures were left in the open for 20 minutes before 
titration.   Anyways to cut to the chase... Two explanations I would like 
to give for possible erros are:  (a)  ethanol evaporated from the beaker 
before the titration was performed  and (b)  the stock solution of 
'absolute ethanol' absorbed water from the air making it not a pure 
"solvent system" -- would anyone know what %age the EtOH would be after 
absorbing water? (ie. ?95%?, 90%?)

Also, does anyone know how to remove a His tag from the C-terminus of a 
protein after Ni-affinity chrom. purification -- would 
carboxypeptidase do 
the trick? or are there other enzymes that would do this?

Thanks in advance for responses and for reading the post!

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