on-rate vs. off-rate

Graham Shepherd muhero at globalnet.co.uk
Tue Feb 1 16:45:12 EST 2000

Esbjorn Fiers <esfie at gengenp.rug.ac.be> wrote in message
news:3896D799.237755F1 at gengenp.rug.ac.be...
> Dear all,
> I am working with scFv phage display libraries. In some articles I come
> across the words on- and off-rate, being the rate at which an antibody
> binds its antigen and the rate at which an antibody dissociates from its
> antigen. Furthermore, they say that when antibody affinities become
> higher this is mostly due to a lower off-rate, with the on-rate being
> less important. I kind of have problems to completely understand this.
> Is there anybody who could explain this to me, or has anyone a reference
> in which this is clearly explained?
> Thanks!
> Esbjorn Fiers
> --
> ==================================================================
> Esbjorn Fiers
> DEPARTMENT OF GENETICS                         Fax:32 (0)9 2645349
> UNIVERSITY OF GENT, K. L. Ledeganckstraat 35, B-9000 Gent, Belgium
> Vlaams Instituut voor Biotechnologie                           VIB
> mailto:esfie at gengenp.rug.ac.be        http://www.plantgenetics.rug.ac.be
> ==================================================================

The on-rate depends on the antigen and antibody coming into close
association spatially to form a complex, and the rate is mainly influenced
by diffusion of the entities in the surrounding medium. Once the
antigen-antibody complex has formed, the off-rate depends mainly on the
strength of the association, which is basically the antibody affinity. The
higher the affinity, the lower the off-rate. There is data somewhere that
I've seen which measures the length of time that the complex persists; for
low affinity antibodies the time was measured in milliseconds; for high
affinity antibodies times were up to 35 seconds. These data relate to
solid-phase bound antigen complexing and decomplexing with soluble phase
antibody. Rates for soluble antigen and antibody will be different.


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