Journal of Lipid Research, Vol 26, 790-796, Copyright © 1985 by Lipid Research, Inc.
Monoclonal antibody to rat apoC: multiple binding to apoC-I on lipoproteins increases its affinity constant
L Wong
Using solid phase systems, the kinetics of binding of monoclonal antibody
(LRB 45, IgG2b,kappa) to apoC-I and apoC-I on lipoproteins were
investigated. At 25 degrees C, the association constant of LRB 45 antibody
to apoC-I (3.56 X 10(6) M-1 X sec-1) was almost three times slower than the
association constant LRB 45 antibody to lipoproteins (10.4 X 10(6) M-1 X
sec-1). However, the dissociation constant of apoC- I from LRB 45 antibody
(0.865 X 10(-4) sec-1) was also slower than the dissociation constant of
lipoprotein from antibody (1.5 X 10(-4) sec- 1). Thus, the calculated
affinity constant (association constant/dissociation constant) of LRB 45
antibody for apoC-I was approximately half of that for lipoproteins (4.12 X
10(10) M-1 vs. 6.92 X 10(10) M-1). The intrinsic affinity constants for
antibody binding to apoC-I and apoC-I on lipoproteins were determined by
Scatchard analysis. The intrinsic affinity constant of antibody bound to
apoC-I was estimated to be 5.49 X 10(10) M-1 whereas that of antibody
binding to lipoproteins was 30 to 200 times less. Furthermore, ascites
fluid from LRB 45 cell lines could immunoprecipitate serum lipoproteins.
Thus, it is concluded that there is multiple binding of antibody to apoC-I
on lipoproteins. This binding appears to increase the calculated affinity
constant (avidity) for antibody-antigen interaction.
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