Re: AAA of MetSO

Rod Levine (rlevine@nih.gov)
Tue, 10 Feb 1998 13:13:30 -0500

At 09:05 AM 2/10/1998 -0600, Lawrence J. Dangott wrote:
>Does anyone have experience in analyzing for methionine sulfoxide? I seem
>to recall that we should use alkaline hydrolysis as the methionine
>sulfoxide will be converted to methione in acid.

You're right that methionine sulfoxide is readily reduced back to
methionine during acid hydrolysis, but not alkaline. However, alkaline
hydrolysis is a pain, so we prefer to take advantage of the effect of
cyanogen bromide, which converts methionine to homoserine (and homoserine
lactone). Methionine sulfoxide is not modified by CNBr.

The protein is treated with CNBr before acid hydrolysis. Thus, the
original methionine sulfoxide gets reduced back to methionine during
hydrolysis and is quantitated as such.

If you have enough material to split the sample into two, you can treat one
half with CNBr but not the other. This is an easier way to get total
Met+MetSO, instead of having to quantitate the original Met as the sum of
homoserine and its lactone.

Rod Levine

NIH
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