106 IMMUNO-CATALYSIS 



7. The Concepts of "Proteinogen" and Enzyme Precur- 

 sors Considered in the Light of the Specificities of 

 Antigens and Antibodies and Their Digestion Products 



Northrop (1946, 1948) has conceived the idea that normal proteins, 

 enzymes, antibodies, viruses are derived from a "proteinogen" or "ur- 

 protein" by a purely catalytic, or autocatalytic reaction which does 

 not require energy. The synthesis of the "proteinogen" molecule, re- 

 quiring energy from another source, is, likewise, assumed to be auto- 

 catalytic. The proteinogen molecule possesses the general chemical 

 structure characteristic of the species. The formation of the above 

 mentioned biologically and chemically specific proteins from the master 

 proteinogen molecule is considered as analogous to the formation of 

 pepsin and trypsin from their respective precursors. Assumption is also 

 made that by such transformations from proteinogen to specific pro- 

 teins the latter acquire specific enzyme and immunological properties. 



If we understand Northrop's postulates correctly, they imply that the 

 derivation of the specialized functions of various proteins found within 

 a kind is associated, or brought about, by an autocatalytic reaction 

 which is capable of converting proteinogen molecules into many differ- 

 ent species of protein molecules. On this basis, enzymes, such as 

 lysozyme, d-ribonuclease, cytochrome c, with molecular weights of 

 about 15,600, myoglobin (mol. wt. 15,900), lactalbumin (mol. wt. 

 17,400) etc. which are structurally, enzymatically and serologically 

 different from species specifically related proteins have acquired 

 these specific properties during their autocatalytic geneses from pro- 

 teinogen molecules. Since, as stated by Northrop, the molecular weight 

 of the proteinogen molecule is equal to or greater than that of the 

 protein derived, and since the autocatalysis in these conversions does 

 not require energy, it must be assumed that: (a) there must be as 

 many specific proteinogens as there are specific proteins. For example, 

 molecular weights for certain specific proteins are: pepsinogen, 42,000; 

 pepsin, 38,000; chymotrypsinogen and chymotrypsin, about 40,000; 

 and trypsinogen and trypsin, 35,000; (b) it must be assumed that the 

 master proteinogen molecule must have a molecular size larger than the 

 largest specific molecule found in a species, so as to be autocatalytically 

 convertible to all molecular sizes; or (c) there must be a proteinogen 



