Re: Methionine oxidation: effects on tryptophan?
chris halkides (halkidesc@UNCWIL.EDU)
Sat, 16 Jan 1999 11:10:59 -0400
> We are studying the effects of methionine oxidation on the function
>of a protein that also contains tryptophan. Following conversion of Met
>to the sulfoxide by means of hydrogen peroxide (1:50), we find upon
>sequence analysis that tryptophan has been largely replaced by an
>derivative eluting earlier, just before proline, from our ABI 477 system
>(time 19.03 min, compared with Pro 19.93, DPTU 23.33, bona fide tryptophan
>24.95 min on the usual NaAcetate/ isopropanol/acetonitrile gradient).
>Tryptophan appears normal in control preparations incubated with solvent
>alone (.1% TFA pH 2.0, 37 deg, 45 min).
> Reports I've found, dating back a long time, indicate that
>tryptophan is not affected by these oxidation conditions. Has anyone seen
>this derivative, and if so does it represent serious damage or
>modification prior to sequencing?
> Thanks very much for any suggestions!
> Henry T. Keutmann, MD
> Endocrine Unit, Massachusetts General Hospital
> Boston MA 02114
> Tel. 617-726-3966
> Fax 617-726-7543
> Email Keutmann@helix.mgh.harvard.edu
Hello Henry,
Certain conditions can potentially catalyze trp oxidation from
hydrogen peroxide. See Means and Feeney, p. 163, Chemical Modification of
Proteins. These include the presence of organic acids and dioxane.
Chris Halkides
Christopher Halkides
Dept. of Chemistry, UNCW
601 S. College Road
Wilmington, NC 28403-3297
(910) 962-7427