As Beverley has indicated, the molecular weight of serum albumin is nearer
67 kDa than 16 kDa, as can be seen by running it on SDS PAGE (which can also
show small amounts of albumin polymers sometimes). As also pointed out,
albumin can undergo glycation in vivo and this obviously makes for a
heterogeneous molecular weight. Other molecules can also bind
non-covalently. There are 35 Cys present which form 17 disulphide and one
nominally free Cys (at position 34, if I remember correctly). If you do a
thiol assay on serum albumin from commercial sources, however, you typically
find that there is an average of 0.15 to maybe 0.4 or so free thiol per
albumin molecule. Careful reduction can regenerate one free thiol per
molecule, while not breaking the 17 disulphides. It seems, then, that the
nominally free Cys in most albumin molecules is covalently bonded to other
molecule, with glutathione being a possible candidate.
Bryan Smith
Celltech R+D
-----Original Message-----
From: Beverly DaGue [mailto:Beverly.B.DaGue@vanderbilt.edu]
Sent: Monday, February 26, 2001 1:59 PM
To: Recipients of ABRF List
Subject: BSA Molecular Weight
Please see the following reference for additional information:
"Primary Sequence and Glycation at Lysine-548 of Bovine Serum Albumin"
by Yoshinao Wada in Journal of Mass Spectrometry, Volume 31, 263-266
(1996). Sequence information in this report gives MW (avg) of BSA as
66429.125 Da.
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