IV. THE TRANSMISSION OF PROTEIN CHANGE 27 



naturase of the protoplasm protein. On the other hand, rennin is an 

 enzyme which is known as a typical denaturase, and actually there 

 seems to be a close similarity in their nature between this enzyme and 

 viruses. 



Casein from milk is coagulated by this enzyme, and its coagulating 

 action has been described as a conversion of caseinogen into casein or 

 of casein into paracasein. Rennin seems to cause in casein molecules 

 a physico-chemical change leading to the coagulation. Haurowitz (60) 

 considered that rennin causes a slight unfolding of the peptide chains 

 of casein, by which polar or ionic groups of the casein molecules are 

 rendered mutually accessible to one another and are thereby able to 

 form intramolecular salt like bonds. A similar argument may be made 

 with viruses, that is, the action of a virus consists in the conversion 

 of virogen or provirus into the virus ; the precursor, of course, must 

 be the normal protoplasm protein, in which polar groups may be liberated 

 by the unfolding of the peptide chains, thereby protoplasm may be 

 coagulated into minute particles and the rearrangement of the peptide 

 chains following this unfolding may lead to the appearance of the virus 

 activity. 



According to the writer's study (61) rennin is similar to viruses 

 in its physical and chemical nature, and its activity is associated with 

 virus-like particles composed of a protein and lipids like viruses. So 

 far as his study confirmed, rennin was stable in such virus-like parti- 

 cles, which become extremely labile when decomposed into smaller par- 

 ticles just as in viruses. Moreover, the enzyme particles isolated by 

 the writer proved to bear a striking resemblance to viruses such as 

 vaccinia and phage in many other respects, that is, in the behaviour 

 towards inorganic salts and pH changes of the solution, and also in the 

 agglutinability at a weakly acid pH ; its isolation was achieved by 

 applying this latter property as with viruses. It is a well known fact 

 that some plant viruses can be crystallized, while rennin was likewise 

 prepared in a crystalline form (62). Such a crystallizable character is 

 never in discordant with its particulate nature, as will be discussed 

 later in another chapter. 



Between the enzyme and viruses, however, there exists an essen- 

 tial difference ; namely the protoplasm protein coagulated by a virus 

 into minute particles can exhibit the virus action, whereas coagulated 

 casein fails to act as the enzyme. Nevertheless, an evidence can be 

 presented that casein molecules that are being coagulated by rennin 

 can promote the coagulation of other molecules. Thus, the length of 

 time for the coagulation of milk by rennin was found to be governed 

 not only by the concentration of rennin, but also by that of milk. The 

 milk solutions of a series of concentrations, to each of which was 



