partial reduction of IgM

[Frederick Garbrecht]

I am trying to partially reduce a murine IgM to the 's' fragment using
cysteine, as described in "Current Protocols in Immunology".  I purify the
reaction mixture over a long Sephacryl S300 column and get 2 major peaks
(UV monitoring).  I then dialyze the fractions containing the peaks,
concentrate them using Centricons, and then do SDS-PAGE.  The first peak
is native IgM, but there is nothing on the gel for the second peak (on
multiple occaissions)! Help, what am I doing wrong?

F Garbrecht
Medical College of Wisconsin
fgarbrec at post.its.mcw.edu