Properties of non-enzymatically glycosylated proteins.

Mark Yeager yeager at sc2a.unige.ch
Thu Mar 12 05:39:04 EST 1992


In article <23789.9203111243 at subnode.susssys1.rdg.ac.uk>,
skrshaw at sksscsc1.rdg.ac.uk writes:

> 	In attempting binding assays involving suspended macrophages, I have found that
>  an almost constant percentage of the label is bound despite the amount of cold
>  ligand added, as expected of non-saturable, non-specific binding to both the
>  cell surface

How do you define specific binding? If you mean a low number of "high
affinity" sites, then your "classical" analysis should work. But of course
things are never that simple, and it is likely that you could have, if it
exists, a "receptor" for the NEG proteins with an affinity of the same
magnitude as nonspecific binding. Then you need some other tricks.

One possibility  is to "enhance" the interaction by making it multivalent.
If the receptors are freely diffusible in the membrane of the macrophage,
then low affinity interactions (but "specific" in the sense of a definite
receptor) can be multliplied by binding oligimers of the ligand (dimers,
trimers, etc.). If the "real" nonspecific binding affinity does not also
increase by the same phenomenon, then you have your signal. The association
constant for the multimers should go roughly as the power of the number of
N-mers: Ka**N. And don't forget that the multimeric effect can be realized
by presenting the ligands on a surface (i.e, they don't have to be close in
space like a dimer, but can be on an apposing membrane or other surface,
like a basement membrane). Some references that can get you started in this
direction:

K Matsui et al, Science 254, 1788 ('91)

SK Dower et al in "Cell Surface Dynamics: Concepts and models" Marcel
Dekker, Basel ('84), AS Perlson, ed., pp. 277-328

Dower et al, Biochemistry 20, 6326-6340 ('81) ( 2 papers)

--   -.-
Mark Yeager  ->  yeager at cgeuge52.bitnet     yeager at sc2a.unige.ch
 University of Geneva, Dept. of Biochemistry, CH-1211 Geneva 4, Switzerland



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