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Peptide Synthesis > Solubility
Solubility and Use of Synthetic Peptides
Crude peptides are precipitated with ether and purified peptides are lyophilized from
0.05% TFA/acetonitrile solutions. Although synthetic peptides are often dissolved first in
water, such solutions may be acidic due to residual TFA and other acids. Several
approaches are available for dissolving peptides that are not soluble in water - with the
approach varying somewhat depending upon the nature of the peptide. Hence AnaSpec, Inc.
suggests the following:
- Acidic peptides may be solubilized by dissolving first in a small amount of a weak base
(e.g., 10% ammonium bicarbonate) followed by dilution with water to the desired
concentration. This approach is not recommended for use with cysteine containing peptides.
- Basic peptides may be solubilized in dilute acid (e.g., 30% acetic acid) followed
by dilution with water.
- Hydrophobic peptides may dissolve in DMSO - which again may be followed by dilution with
water.
- Peptides that are prone to aggregation may require strong denaturants (e.g., 6 M
urea, 6 M urea with 20% acetic acid, or 6 M guanidine-HCL) which may (or may not) then be
able to be diluted.
Because synthetic peptide analogues often do not assume the same conformation as
the corresponding stretch of sequence in the native protein from which their sequence is
derived, structure/function studies that are carried out with synthetic peptides must be
interpreted with caution. In this regard, a frequent control that is used to try to
differentiate the impact of amino acid sequence and structure versus the composition on
the "activity" of the peptide that is being monitored is to study the properties
of a similar length and composition synthetic peptide whose sequence has been randomized (i.e.,
references 6 and 7 in Keck Publications.)
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