Psq : retention time of oxidized methionine
Dan Brune (DBrune@asu.edu)
Thu, 07 Jan 1999 17:10:39 -0700 (MST)
Suzanne,
My somewhat anecdotal experience indicates that, at least with my
Porton sequencer with the pth amino acids being separated on a C18 column
using the standard Porton gradient, oxidized methionine elutes with the
same retention time as threonine. The evidence for this is as follows:
1. Several times I have seen a minor threonine peak accompanying Met in
otherwise rather clean protein samples.
2. In one instance, this "Thr" peak was quite large relative to the Met
peak at a position in a protein where a subsequent gene sequence indicated
that the correct amino acid was Met. CNBr cleavage of the protein at this
Met position was very inefficient, as would be expected if the Met residue
was oxidized to Met sulfoxide.
As the elution pattern of amino acids is with ABI instruments is
rather similar to the pattern with the Porton system, I expect that the
general location in your chromatograms will be the same. You can probably
confirm this simply by heavily overloading a protein disk with Met
sulfoxide from one of the biochemical companies and running a couple of
cycles of sequencing. I have previously used this strategy to confirm
retention times of N-methyl Ala and of hydroxyproline.
Best wishes,
Dan Brune
Dept. of Chemistry & Biochemistry
Arizona State Universty