Linus Pauling: Well I think we have an understanding of the molecular basis of biological specificity. Why do people become allergic to
strawberries, say, or to milk, or something like that? This is the same subject.
The antibodies are protein molecules which have a region which is complimentary in structure to the antigen. For example,
the benzene arsonic acid, a group that Landsteiner was fond of working with. We were able to show that the antibody molecule,
the atoms in the antibody molecule, fit around this group, the heptanic group, very closely to within about a quarter of an
atomic diameter, on the average, and that they bring into juxtaposition groups that are complimentary to certain groups in
the heptan.
For example, an electron pair donating- hydrogen bond-forming atom will come up close to a hydrogen atom attached to an electronegative
atom, so that a hydrogen bond is formed. And a negative charge will be brought up in the neighborhood of a positive charge
in the heptanic group, and so on, all contributing to the weak intermolecular forces that operate. Now it is the shape factor
that’s responsible for the specificity.
We found that if antibodies were made against benzene arsonic acid, they would not combine with meta-chloral-benzene arsonic
acid, that had a chlorine atom, 181 femtometers - I’m trying to learn to talk in the international system of units - 181 femtometers
in diameter here, because the hole into which a hydrogen atom, 110 femtometers in radius would fit, is not big enough for
the chlorine atom to get into. But if you made antibodies against the meta-chloral-benzene arsonic acid group, which have,
the antibodies have a hole big enough for this chlorine atom, then the benzene arsonic acid will fit in, because the hydrogen
atom is smaller and it can slip into the larger hole. That sort of thing. Very, very satisfying it was to me to feel that
this puzzling phenomenon of species specificity of antibodies, antiserva, could be understood.
