RE: Pepsyn: Difficult Sequence
Russ Henry (russ@peptide.chem.unc.edu)
Wed, 11 Feb 1998 10:34:53 +0500
Trudy,
When synthesizing a peptide it is useful to calculate the % of
theoretical weight gain for the resin. This will give you a quick way of
seeing if the AAs went onto the resin. Some synthesizers calculate the
theoretical weight gain for you. If yours doesn't, you can do it manually
from the resin substitution, synthesis scale, and molecular weights of the
protected amino acids. A good rule of thumb is that the % of theoretical
weight gain should be (100-# of AAs), or in your case 82%. Another thing
to do is to weigh the peptide after cleavage to see if the cleavage/ether
extraction steps went well. A slightly acidic/hydrophobic sequence like
yours may not have completely precipitated in the ether. Also, assuming
you are using TFA as the ion pairing agent in your HPLC runs, your
sequence looks like the type (slightly acidic/hydrophobic) that may not
chromatograph well under those conditions. You might want to try
substituting 0.1m NH4AC or TEA-AC at a pH of 6-6.5 for the TFA.
Good Luck,
Russ Henry