From: Geoff_Howlett.BioChem@muwaye.unimelb.edu.au
  To  : rasmb@bbri.eri.harvard.edu
  Date: Tue, 30 May 1995 08:03:42 +1000

Acetonitrile causes floating?

Hi

Yesterday I saw something bizarre.

A recombinant protein (MW about 20000) was re-purified by reverse-phase 
HPLC, freeze-dried to remove acetonitrile, resuspended in aqueous buffer 
(final conc ~6 mg/ml) and analysed in the XLA U/C.  The speed was 3000 rpm 
and data was collected at 295nm (4 scans 10- mins apart).  To be honest 
the sample was a bit cloudy and attempts to clarify it using the microfuge 
were only partly successful.

To my surprise a significant proportion of the sample (20%) actually 
floated.  The easiest explanation is floating was due to residual 
acetonitrile (density 0.78 mg/ml) bound to the protein.  Has anyone else 
seen this happen?  It makes me wonder whether HPLC purification may 
unwittingly introduce artifacts which sometimes go unnoticed.  

It could explain a few things...

Let me summarise your responses.

Cheers

Geoff Howlett
Department of Biochemistry and Molecular Biology
University of Melbourne
Parkville 3052
Australia

FAX	61 3 347 7730
PH	61 3 344 7632

E-mail:	g.howlett@biochemistry.unimelb.edu.au