Evolution.

Society for Experimental Biology (Great Britain)

Date:: 1953

Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Evolution. Source: Wellcome Collection.

479/484 (page 447)

POSTSCRIPT 447 The same process may be involved in the development of resistance to drugs. For example, trypanosomes may become separately and inde¬ pendently resistant to each of the three types of arsenoxide shown in Fig. 2. All three compounds are of the type which normally diffuse rapidly into cells. Resistance to these compounds probably involves the develop¬ ment of an active transport mechanism which pumps them out of a cell as fast as they penetrate (Danielli, 19526). Fig. 2. For explanation see text. These active transport mechanisms show a high degree of chemical specificity—of the same order of magnitude as that found with antibody- antigen reactions. This resemblance at once suggests a mechanism for deriving new or modified active transport systems. Antibody formation is elicited by subjecting cells to foreign substances. The ability to form anti¬ bodies persists long after the foreign substance has vanished, and is therefore 'self-reproducing'. The ability to form specific antibodies is handed on from cell generation to generation. Antibody formation is thus a specific directed adaptation to foreign substances. Pauling has shown that if proteins are exposed to small foreign molecules in certain circum¬ stances, the proteins exhibit a specific adaptation determined by the foreign molecule, similar to that exhibited by antibodies. These facts suggest that some forms of directed adaptation involve the formation of new or modified active transport units by a process analogous to antibody formation (refolding of high-polymer chains?). Looked at in this light, some forms of directed mass adaptation appear neither anomalous nor heretical. Having reached this point it is perhaps worth reñecting upon the probability that active transport mechanisms are much more primitive than is the production of antibodies, and that the formation of antibodies in higher animals may well be a process which has evolved from active transport mechanisms. Active transport mechanisms, like antibodies, may, so far as present evidence goes, be regarded as plasmagenes, capable of ' self-reproduction ' and of mutation. It is also important to realize that recent work on bacterial transforming factors makes it possible that many adaptations involve both the presence of the rare individual carrying a mutation, and also mass adaptation. For example, from the work of Hotchkiss (1952) on bacterial transformers