54 IMMUNO-CATALYSIS 



protein from its hydrolytic products. This would mean that the host 

 enzyme would catalyze the reactions of a foreign protein only in a 

 forward direction: 



host host 



enzyme enzyme 



Foreign protein >- amino acids ^ host protein, etc. 



This relationship is particularly worthy of consideration when we 

 are dealing with artificial conjugated antigens. These differences in 

 the rates of the metabolism of species specific and foreign proteins, or 

 the failure to metabolize a foreign protein by a host could no doubt 

 account for the longer life of a foreign substance in a host as will be 

 discussed below. This relationship is of fundamental significance in 

 the production of antibodies to foreign substances. 



A foreign protein may possess component units uncommon to the 

 host species. Many microorganisms possess unusual proteins or poly- 

 peptides composed of single or different unnatural amino acids, and 

 non-protein uncommon substances as well. Ivanovics and Bruckner 

 (1937, 1940) found that the specifically precipitable capsular sub- 

 stance of B. anthracis is a polypeptide-like substance of a molecular 

 weight of about 6000 made up solely of 40 to 50 d-glutamic acid 

 residues. According to Hanby and Rydon (1946) the capsular sub- 

 stance is made up solely from d-glutamic acid residues. The molecular 

 weight of the native material is greater than 50,000 and is thus of the 

 same order of size as many proteins. Structurally, the capsular sub- 

 stance is a long chain molecule made up of a-peptide chains of 50 to 

 100 d-glutamic acid residues joined together by y-peptide chains of 

 d-glutamic acid residues. Since d-glutamic acid is of unnatural optical 

 configuration the proteolytic enzymes of the animal system would 

 either fail to digest or effect the digestion of this polypeptide at a very 

 slow rate. The resistance of this polypeptide to proteolysis would not 

 only confer on it a haptenic role but may also serve as an armor for the 

 microorganism against the host enzymes, prolonging the antigenic 

 activity of the cellular components and virulence as well. The occur- 

 rence of polypeptides which are indistinguishable from that of the 

 anthrax bacillus have been likewise found in the organisms of the 

 mesentericus and subtilis groups. In Saccharomyces cerevisiae a poly- 

 peptide composed of 10 to 12 glutamic acid residues was found to be 



