What is the pI of IgG?

John Ladasky jladasky at cmgm.Stanford.EDU
Sat Feb 21 16:29:34 EST 1998

In article <6ckb1n$mgb at ringer.cs.utsa.edu>,
Brian S. Thoma <bthoma at lonestar.jpl.utsa.edu> wrote:
>>I have been reading through Maniatias, Current Protocols in Mol. Bio.,
>>etc. but I have been unable to find a reference to the pI of IgG. I need
>>to find out since I believe I may have a proteoglycan which elutes off of
>>DEAE not far after the contaminating IgG.
>>If anyone can forward a little wisdom it would be greatly appreciated.
>>Thank you in advance,
>>Brian Thoma
>>Univ. of Texas at San Antonio
>>Extracellular Matrix Laboratory

	Unless you're talking about a monoclonal antibody, the answer is
that IgG has no unique isoelectric point!  Remember that antibody molecules
have variable regions (that's how they get their job done!), and that these
variable regions can include charged residues.  I would guess that isolating
antibodies by molecular weight, say with a Sephadex column, would be more
reliable than isolating by a method which depends on the isoelectric point.

Rainforest laid low.
"Wake up and smell the ozone,"
Says man with chainsaw.					- John Ladasky

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