Antibody/Antigen Structure (fwd)
haoxiao at cc.UManitoba.CA
Tue Jan 17 21:15:34 EST 1995
> A caveat: I have come into this mid-thread and am not the original author. I
> couldn't help but try to straighten out some of this funky chemistry.
> In article <3f0dvs$4eh at nof.abdn.ac.uk>, opt018 at nof.abdn.ac.uk (opt018) writes:
> > Hao Xiao (haoxiao at cc.UManitoba.CA) wrote:
> > : Four major forces are involved.
> > : Hydrophorbic force: act like your ruber sticker on the glass wall. you squeeze
> Hydrophobic force is a peculiar attaction based on the principle of "Like
> likes Like" The above example is actually electrostatic attraction. Glass has a
> net - charge and rubber an effective net positive charge since it is an
> insulator. In fact this example will not work underwater as a ag-ab complex
> can be envisioned as occuring.
You actually missed my original post. My explanation was based on
the energetic analysis. More than one water molecule will be associated
with the surface of "a" Ag and the Ag binding sites of a Ab in the aqeuous
phase. This wil certainly causes loss
of translational and rotational energy. Hydrophobic interaction btw Ag
and Ab will squeeze or free the associated water (air in term of the
ruber sticker) molecules and releases the energy which will be utilized
for the binding or stability of the Ag-Ab complex. That is the
hydrophobic force. The loss of translational energy of one Ag due to the
immobilization to Ab is over payed by release more than one water molecules.
(the translational and rotational energy of a large molecule is only
slightly higher than small molecule like water). Your explanation of
hydrophobic interaction is good and true but hardly provide a relevent
relationship btw affinity of Ab and a drop of oil in water.
> > : Hydrogen and ionic bonding: act like your magnet sticker. Such forces
> Hydrogen bonding is an extreme case of ionic bonding. It is what gives water
> its remarkable properties and is classifies as a force in its own right.
> Electrostatic interactions are much weaker but still quite strong. These are
> cases where one molecule has a strong charge and the other a strong charge of
> the opposite polarity but cannot either a)abstract the electron or b) force a
> covalent bond where the electrons are shared by both molecules.
> > -----
All four forces are not strong as comapared to covalent-bonding.
H-bonding is considered to be
relative strong for Ab-Ag interaction (12 Kcal/M, imagine the energy
required for boiling the water than for bioling acetone). Covalent bond
involves complete overlap of e-orbital, H-bond involves partial overlap
of e-orbital therfore it stil reversible.
> > Nice explainations.
> > ----
> > Question 1: Can London disperse force and Hydrophorbic force coexist in the same
> > Ag/Ab complex pair?
> Absolutely! Ag-Ab complexes rely on all four of these interactions. One alone
> would probably not be enough to overcome the jostling of random thermal motion.
> > Question 2: You mentioned that you can increase the affinity by slightly
> > increase the Ag size, simply because 'more water molecules are squeezed out'.
> > Does this contradict the fact that Ab only recognize a certain fragment of Ag
> > specifically, no matter how big the Ag size is?
> Nope. By increasing any one of the forces, in this case hydrophobicity, you
> can make the ag stick even better to the antibody.
> > Question 3: What is the forth major force? :-)
> Hydrophobic and electrostatic count as two differnt forces in this situation.
> > Thanks a lot.
> > --------------------
> > Yours
> > Y-F D. Cheng, MB ChB
> > Dept Ophthalmology
> > Univ Aberdeen
> > UK
> > <opt018 at aberdeen.ac.uk>
> > <http://www.abdn.ac.uk/~opt018/cheng.html>
> Allen Black
> Dept. of Pathology
> Univ. of Newcastle
> mdcabl at cc.newcastle.edu.au
Ph.D student in Toxicology and Pharmacology
haoxiao at cc.umanitoba.ca
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