Problems with peptide iodination

Cao-Guo Yu cqyu at
Thu Jul 8 13:54:35 EST 1993

We are having a problem with iodination of a
peptide (15 amino acids) that will not dissolve
in the 0.25M phosphate buffer required for the
procedure. We initially dissolve the peptide in
water (1 ug/ul) and add buffer, but this causes
the peptide to precipitate.
   The peptide will dissolve in water, but will
precipitate after freezing and thawing. It also
dissolves in acid 0.1M HCl. The original paper
on it's identification reported that for HPLC
the peptide was dissolved in 0.05M, pH 4 NH4OAc
buffer and eluted from the column with a 0.05M,
pH 7 to 0.8M, pH 7 NH4OAc gradient. We tried to
dissolve it in pH 7 0.1M to 0.8M NH4OAc, but it
would not dissolve.
   Would anyone have any suggestions as to how to
deal with this precipitation problem ?
   Thanks in advance.


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