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.