Haptophoric groups

If we assume that those peculiarities of the toxin which cause their distribution are localized in a special group of the toxin molecules and the power of the organs and tissues to react with the toxin are localized in a special group of the protoplasm, we arrive at the basis of my side chain theory. The distributive groups of the toxin I call the haptophore group and the corresponding chemical organs of the protoplasm the receptor. . .. Toxic actions can only occur when receptors fitted to anchor the toxins are present. 

When Ehrlich had transferred his interests from large molecules to small ones, he drew on part of his side-chain (immunological) hypothesis to explain the mode of action of chemotherapeutic agents. They too, he supposed, had distinct haptophoric and toxophilic groups (he demonstrated this for arsenicals see the end of this section), and they combined with cellular receptors whose normal function was to take part in cellular nutrition or respiration (Ehrlich, 1908). 

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