Isoelectric peptide purification
Henry Keutmann (keutmann@helix.mgh.harvard.edu)
Thu, 18 Mar 1999 17:32:05 -0500
To my ABRF colleagues:
A collaborator has a question regarding the purification of a
tripeptide at or near its isoelectric point. He purified it by HPLC and
wants to eliminate all residual TFA, isolating and lyophilizing it at its
isoelectric point of about 5.3. We should be able to replace the TFA with
ammonium acetate (perhaps with an intermediate treatment with dilute HCl)
for ion-exchange (e.g. mono-S) chromatography.
Firstly, will this effectively remove residual TFA?
Second, after lyophilization what will be the state of the peptide
in terms of salt content: will acetate and ammonium remain as counterions
at the N and C terminus, or is there a way in which they can be removed
(e.g. replaced by water, or preferably retrieved as the noncomplexed
peptide)? Would the salt form be detectable on mass spec?
Thanks for any advice!
Henry Keutmann
Endocrine Unit, Wellman 501
Mass. General Hospital
Boston MA 02114
617-726-3966