Re: Elution position of PTH-methionine sulfoxide
Deb McMillen (mcmillen@morel.uoregon.edu)
Fri, 8 Jan 1999 10:16:25 -0800 (PST)
Hi, all,
Not being a chemist by training, I like to spend some time reading these
bits about amino acids. I looked up methionine modifications in a CRC
Press handbook that I keep tucked by my desk. One study quoted (but I
couldn't find the reference indicated in the text) compared mercaptoacetic
acid, beta-mercaptoethanol, DTT, and N-methylmercaptoacetamide in their
effectiveness in conversion of met sulfoxide to met. Apparently, the last
reagent was the most effective. The reactions demonstrated little pH
dependence but did not proceed well above 50% acetic acid (v/v). Complete
regeneration was suggested with 0.7 to 2.8 M of reducing reagent at 37 deg
C for 21 hours. Perhaps, as Marjorie points out, 25% TFA at 61 deg C in
the conversion flask with DTT present (under the conditions in the ABI
sequencers) is just not adequate to convert all of the met sulfoxide back
to the met.
Keep the chemistry class coming!
Happy New Year,
Deb McMillen
Institute of Molecular Biology
University of Oregon
Eugene OR
On Fri, 8 Jan 1999 marjory.barnes@pharma.Novartis.com wrote:
> Dear Suzanne,
>
> PTH-methionine sulfoxide elutes between Q and T using the
> 5%THF/acetonitrile solvent system on the PE/ABI 473A. The peak is about 1
> 1/2 times broader than the other PTH-amino acids which elute in this
> region.
>
> Methionine sulfoxide is apparently not completely reduced in the ABI 473A
> in spite of the DTT in the sequencer reagents.
>
> I confirmed the identity with PTH-methionine sulfoxide from Research
> Organics Inc., Cleveland, Ohio, 800-321-0570.
>
> Marjory Barnes
> Novartis Pharma AG
> Basel, Switzerland
> marjory.barnes@pharma.novartis.com
>
>