[Protein-analysis] Re: proteins that don't ionize

[PM]

jps wrote:
> Recently purified an unknown protein with a partial N-terminal
> sequence match to a bacterial outermembrane protein.  Oddly this
> protein does not react with DTNB, does not seem to ionize when mixed
> with sinnapinic acid and placed in a MALDI-ToF, and has a molecular
> weight of 33kDa as judged by SDS PAGE analysis.
> 
> Curious to know if anybody thinks that membrane proteins would have
> more difficulty interacting with MALDI matrices than other proteins?

Maybe trie a batch of matrices?
Not all substrates wil "fly" with sinnapinic acid. DHBA? maybe or use 
electrospray (TOF) MS.