From: StvTindall@aol.com
Date: Thu, 16 Jan 1997 11:19:16 -0500 (EST)
Subject: Re: C-terminal blocking of proteins
To: Recipients of ABRF List <abrf@aecom.yu.edu>
On 97-01-15, Ken Williams wrote:
"... Does anyone have any data/know of any references that relate to
occurrence of C-terminal blocking? ..."
----------------------------------------
Ken,
Good question, but there may not be a good answer. Most of the existing
C-terminal data comes from carboxypeptidase studies, but I have never found a
good summary describing the frequency of modified C-terminal residues as
determined by carboxypeptidase/AAA. With respect to data from C-terminal
(chemical) sequencers, I think the answer is sort of anecdotal at this point.
Based upon my experience with C-terminal sequencing, I view "total" blockage
of proteins as a rare event, maybe 1 in 50-100. Naturally occurring peptides
may be a completely different story. In vivo C-terminal amidation of peptides
seems to be fairly common.
If you define partial blockage as getting a lot less signal than
expected (meaning what I expect, not what the submitter expects), it is
common to find proteins that appear to be partially blocked. One public
domain example of significant blockage that comes to mind is human hemoglobin
(alpha/beta). In that case, both subunits give about 20% of the expected
signal.
Steve
P.S. If you get an "off-line" citation for C-terminal blockage, please post
it.
====================
Stephen Tindall
Argo BioAnalytica, Inc.
Phone: 1-201-605-2100
Fax: 1-201-605-2104
StvTindall@aol.com
====================
Subj: C-terminal blocking of proteins
Date: 97-01-15 15:25:35 EST
From: WilliamsKR@MASPO1.MAS.YALE.EDU (Williams, Ken)
Sender: abrf-request@aecom.yu.edu (Association of Biomolecular Resource
Facilities)
To: abrf@aecom.yu.edu (Recipients of ABRF List)
One of the potential advantages of automated C-terminal sequencing is
that it would get by the problem of blocked N-terminals in proteins from
higher eukaryotes. However, this brings up the question of the extent of
C-terminal blocking in higher eukaryotes (and other organisms). Does anyone
have any data/know of any references that relate to occurrence of C-terminal
blocking?
Thanks very much,
Ken Williams