THE SYNTHESIS OF PROTEINS I5 



be accounted for. Autocatalysis, therefore, offers the only escape from 

 the dilemma of the preformationists and has been invoked by a number 

 of workers. Troland (1917) developed a general theory of cell forma- 

 tion on this basis. He concluded that complicated molecules reproduced 

 themselves by a process similar to crystallization. The molecular struc- 

 ture of the underlying layer determined the structure of the superim- 

 posed layer. Troland also reviewed earlier and less definite suggestions 

 of autocatalysis. Koltzoff (1928) developed a similar theory. He con- 

 cluded that antibody formation was a special example of such a reaction. 

 Koltzoff also realized the fact that an autocatalytic reaction cannot 

 start itself, but must have at least one molecule of the reaction product 

 present at the beginning (cf. Northrop, 1937). He assumed the "gen- 

 onema" contains at least one molecule of each protein of the species. It 

 is difficult to avoid the necessity for this assumption but it may be that, 

 if the total number of different kinds of protein molecule present in the 

 individual were known, genonema and even the sperm and ovum would 

 be too small to contain them. Gulick (1938) suggests that protein mole- 

 cules are biscuit-shaped discs and that this structure is impressed on 

 each succeeding molecule somewhat as a coin is stamped by a die. He 

 points out, however, that the contact must be "front to back" as other- 

 wise the impression of the disc and not the replica would be obtained. 

 Langmuir and Schaefer (1938) have also suggested the "template" 

 method of regulating synthesis. Pauling's (1940) theory of antibody 

 formation is somewhat similar. Darlington (1944) ascribes the forma- 

 tion of "plasma germ" and viruses to a similar autocatalytic reaction. 



Stanley (1938a) suggests that a protein-nucleic acid complex is the 

 simplest structure capable of autocatalytic synthesis. He ascribes the 

 specific synthesis to a crystallization-like reaction similar to that sug- 

 gested by Troland. 



A Working Hypothesis for the Synthesis of Proteins 



The preceding section has summarized briefly theories and experi- 

 mental results relating to protein synthesis. These theories account more 

 or less satisfactorily for the specificity of the reaction but (with the 

 exception of the system of Langmuir and Schaefer) fail to provide for 

 the necessary energy. Since there is every reason to believe that energy 

 is required, the synthesis cannot be accounted for by a simple auto- 

 catalytic reaction, nor can it be said that any of the various types of 

 proteins or viruses "synthesize themselves," unless it be further assumed 

 that they are formed from unknown, high energy compounds. They 



