ProtSeq

Laurey Steinke (lsteinke@molbio.unmc.edu)
Tue, 6 Jan 1998 14:14:15 -0600 (CST)

Hello all,
I have a fun little puzzle here. A collegue synthesized a peptide with
the expected sequence: YSFK[N-methyl-aspartate]MPLAR and calculated the
expected mass to be 1241. Both my facility and another performed maldi-tof
MS on the sample in alpha-cyano maitrix and found a molecular weight of
1332. Upon n-terminal sequencing, the sequence YSFKXMPLAR was found,
where X is about 1/10th the size of the major sequence and appears just
after N (on a Procise 491 with 2.1 mm column, premix buffers, adding TFA
and phospate to their A3 and using B2 buffer). I see a few peptides which
seem to be incomplete but all are less than 1/10 the amount of the major,
apparently correct, peptide.

My two questions are:
Why is the mass off so much?
Is the location of the minor peak "correct" for N-methyl-aspartate?

Thanks for your input!

-laurey

Weather Inconsequential: The day is grey and gloomy with the remains of an
ice storm making walking unpleasant. Luckily, we have a box of Christmas
present chocolate to lift our spirits!

Laurey Steinke
Protein Structure Core Facility
University of Nebraska Medical Center
Omaha Nebraska, 68198-4525

Phone (402) 559-6647
FAX (402) 559-6650
lsteinke@molbio.unmc.edu