Peptide solubility problems

FAR3 far3 at
Thu Feb 9 18:06:08 EST 1995

Help! I am performing MHC/peptide binding assays by FACS but having
terrible problems with peptide insolubility following HPLC purification
(elutes @ 30% acetonitrile) and freeze-drying (sequence
 I have tried dissolving in PBS, DMSO,and acetonitrile. Initial dissolving
is in
Guanadinium prior to HPLC, but this doesn't agree with cell culture (20h
with EBVs). Any suggestions?

Even though you are dissolving the peptide in PBS it is probably still in
the protonated form - coming off the hplc column that uses TFA in the
aqueous phase.  I recommend raising the pH with some solid sodium
bicarbonate added a small amount at a time with gentle vortexing.  You can
monitor the pH with 10 ul of the solution place onto a small piece of pH
paper.  This peptide will be soluble up to 1 mg/ml but the pH must be
above 6 and preferably above 7.

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