Haptophoric Group

HAPTOPHORIC GROUP, a term introduced by Ehrlich in his theory of side chains. The study of the relationships between toxins and antitoxins in vitro and in vivo showed Ehrlich that the strength of toxins, measured by their minimum lethal dose for an animal, and the ability of toxins to be neutralized by a certain amount of antitoxic serum, are not in constant relationships to each other. The first quantity is unstable, while the second is characterized by great stability. In view of this, Ehrlich postulates for the toxin molecule the existence of two groups: the toxophoric group, which causes the poisonous effect of the toxin on the cells of the animal organism, and the haptophoric group, which causes the binding of the toxin to the receptors of the corresponding antitoxic serum. By analogy with toxin and antitoxin, Ehrlich calls the haptophoric group in general the receptors of cells that cause the reaction of binding antigen to them (see), in contrast to the zymophoric group, which determines the nature of changes in the bound antigen. [The figure shows a cell with two receptors (ft) with a haptophoric group (a), capable of binding a specific substance (d), and a zymophoric group (c), causing corresponding changes in this substance, for example: coagulation, release into the blood. These receptors function as agglutinins, coagulins, etc.].