Re: Protein sequencing: retention time of oxidized methionine

Rod Levine (rlevine@nih.gov)
Fri, 08 Jan 1999 16:37:13 -0500

At 10:32 AM 1/8/99 -0800, Deb McMillen wrote:
>Rod, I was wondering if there are mets that are so buried or in a
>microenvironment (I love that term) that CNBr cannot attack them--even
>though they are met and not met sulfoxide. I've always understood that
>CNBr maps of proteins were most likely not going to be complete--but is
>that only dependent on the presence of met sulfoxide sites?

Deb,

There generally aren't any exposure issues under the usual conditions for
CNBr cleavage. It's typically done in 70% formic acid or TFA, sometimes
even with guanidine. Cleavage can be done at room temperature overnight,
but many of us do it at 70 C because it's complete in 1 hr.

I've always thought that these harsh conditions, coupled with the basic
nature of the CNBr oxidation, accounted for impressively complete cleavage.

Rod Levine

NIH
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