protein mass spec problem
Marcus, Dr J.
J.Marcus at botany.uq.edu.au
Tue May 6 17:40:08 EST 1997
Your added 129 Da could be explained by an added glutamic
acid, 125 Da would be explained by an additional glutimine
or lysine residue, 105 comes close to the mass expected for
an added cys (i.e. 103.2). How you are getting these
additional residues from an expressed sequence is another
matter which escapes me. Is it possible that stop codon
(TAA) could be mistaken for a glu codon (GAA)? This might
explain how you are getting the extra 129 Da. This seems a
bit far out but maybe it is worth considering. Hope this
> Analysis of the pure protein by electrospray mass spec. produces four peaks.
> Peak one corresponds to the mass predicted from the gene sequence (40287).
> Peak two is the mass of peak one plus 129.
> Peak three is about 125 mass units larger than peak two.
> Peak four is about 105 mass units larger still.
> The heights of peaks one and two are similar, peak three is about half
> as big, and peak four maybe half as much again.
> Does anyone know why we might be getting these multiple forms?
> The protein was purified in Tris buffer,
> 5mM ammonium sulphate, 1mM dithiothrietol and dialysed
> against water before mass spec.
> John Fox
John Marcus Marcus at tpp.uq.edu.au (Dr J.Marcus)
Cooperative Research Centre for Tropical Plant Pathology
5th Level John Hines Building
University of Queensland
St. Lucia, QLD 4072
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