The photoaffinity group of choice is p-benzoylphenylalanine (Bpa), which
you can buy as a Boc or Fmoc derivative. Bpa activates with 300-350 nm.
Peptide with Bpa may be cleaved with HF, I am not sure about iodination,
but you can easy check with a not-expensive benzophenone and your
iodination reagent.
The only precaution is: do not use EDT as a scavenger together with Bpa.
Bpa is a bulky molecule that can alternate the binding of the peptide to
receptor. If you want to make a replacement of other aminoacid to Bpa,
I would replace the hydrophobic (Leu, etc.) in order to try to preserve
the activity.
Because
1)iodination may also change the activity, since the size of the iodine
atom is almost the size of the aromatic ring and...
2) iodination sometimes happens not only at the desired aminoacid, but
at other side chain(s) (like His, or if you have more than one Tyr, you
can not iodinate one of them only)...
you may want to synthesize peptide with Bpa and iodinated (I 127) amino
acid, that you can buy, like Boc/Fmoc mono(or di-) iodo-Tyr, purify by
HPLC check the activity, sometimes even check binding and then, if you
like the results, prepare the radioactive material by the exchange of
iodine 127 to iodine 125 at 90C with NaI(125).
Michael Breslav
R.W. Johnson PRI
Spring House, PA
> ----------
> From:
> Haaseth@brcf.med.umich.edu[SMTP:Haaseth@brcf.med.umich.edu]
> Sent: Thursday, January 15, 1998 1:07 PM
> To: Recipients of ABRF List
> Subject: PEP SYN: Photoaffinity Probes
>
> Dear ABRFers:
>
> OK, I have several questions:
>
> What do you you like to use as a photoaffinty reagent
> for peptides? What is commercially available; where do
> you get it?
>
> I see Bachem has p-azidoPhe available in both Fmoc and Boc
> forms. Do you like to use this? If so, what wavelength
> of light do you use to activate it?
>
> Will the conditions (Chloramine T) for radioiodinating a
> tyrosine residue do any damage to the p-azido (or other
> appropriate) group before binding and subsequent
> photoactivation?
>
> Thanks in advance for any help you can offer.
>
> Ron Haaseth
> University of Michigan
> verdin@umich.edu
>