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From: depquw@gw.unipc.ulg.ac.be (De Pauw Edwin)
Subject: peptides sequencing
Date: Mon,26 Jun 1995 15:09:04 +0200
Organization: Liege University

IOligopeptides sequencing can be performed using liquid SIMS or 
electrospray ionization. If the interpretation of spectra of known
compounds is easy, structure determination of unknowns is however
not so direct. Fragmentation does not often give all the structural
information needed. Two methods can then be used: the brutal force 
or MS/MS. The brutal force means fitting the spectra on the basis of 
the amino acids combinations. If their nature can be deduced from the
low mass iminium fragments, the task is simplified. The other way is
the use of MS/MS. Daughter ion spectra are usually employed. We used
in addition the fact that b-a ions are often present to selectively
pick the b-a transition by constant neutral loss of CO. This scan 
labels the fragments as b ones. In electrospray, multiply charged ions
are the source of most fragments. We recently observed the loss of CO
and water from doubly charged ions on a triple quadrupole instrument,
resulting, as expected, from the apparent loss of half the mass monitored
(double charge). In sector instruments, the same sample gaves not 
the same results. We think that calibration of linked scans do not work
for losses from multiply charged ions. Before to start ourselves 
the scans calculation, we would like to know if someone already made
the job.  
Thanks

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From: strecker@chemie.fu-berlin.de (Andreas Strecker)
Subject: Re: peptides sequencing
Date: Fri, 07 Jul 95 20:09:04 GMT
Organization: FU Berlin

There is also now the posiibility to sequence with MALDI-MS and 
post-source-decay (PSD) technique. The first machines are already on the  
market. The technique uses the "natural" fragmentation that occurs subsequent 
to acceleration of the ions after MALDI. The fragments get a secondary 
acceleration and are detectable as a fragmentation series of the original 
molecule. This makes peptide sequencing possible. Major advantages: Little 
sample amount required; low purity of sample required (peptide mixtures or 
even complete digest probes are sequencable); ions differing in less than 50 
masses may be separated prior to sequencing within the MS by way of an 
electronic switch. Major disadvantage: Only few machines installed yet (but 
numbers are rapidly growing!)

Andreas

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From: vilboisf@iprolink.ch (Francis Vilbois)
Subject: Re: peptides sequencing
Date: Sat, 08 Jul 1995 23:55:07 +0100
Organization: Internet ProLink

I have never seen any good data from these MALDI-MS PSD techniques. The
mass spectrometers on the market are absolutely useless. 

Francis

-- 
Francis Vilbois

e-mail: vilboisf@iprolink.ch 

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From: Ashley McCormack <alm7203@u.washington.edu>
Subject: Re: peptides sequencing
Date: Mon, 10 Jul 1995 17:12:51 -0700
Organization: University of Washington
Nntp-Posting-User: alm7203
In-Reply-To: <3tm6ch$dhs@acmex.gatech.edu>

While it is time consuming and sometimes difficult to sequence by MS/MS 
it is not impossible to sequence unknowns. Just look at the elegant 
work of Don Hunt's group in the last few years, sequencing MHC peptides 
using triple quadrupoles. 

While MALDI TOF instruments capable of PSD are a welcome addition to the 
techniques available, metastable fragmentation has been available to 
biological mass specrometrists for some years.  It may produce 
different ion series that low- or high-energy CID but the ion series 
produced by those methods usually provide the information necessary to 
sequence peptides.  And some peptides just won't fall apart the right 
way, no matter what you do to them.

While I am a fanatical micro-LC/ESI/MS/MS triple quad user, IMHO 
whatever method works to get the answer is the one to use.

Ashley L. McCormack
UW

Just my two cents, not my employers.