2 20 PROTEIN (NITROGEN) METABOLISM OF BACTERIA 



While it cannot be so easily proved, interchanges of nitrogenous materials must 

 take place in a somewhat analogous manner. Complex nitrogenous compounds must 

 be split into their simple ionizable constituents before they become available for cell 

 nutrition. In the words of Abderhalden/ ''No cells can directly assimilate and utilize 

 foreign food material. The latter must be prepared for the cell (by enzyme action)." 

 He likens this transformation to the conversion of a church building into a school- 

 house, in which the church must first be reduced to the individual bricks, etc., and 

 then built up again into the new structure. 



Abderhalden's statements were directed mainly to animal physiologists. It was 

 he who apparently first showed by actual experiment that man and the higher animals 

 depend upon the hydrolysis of complex nitrogenous food in the stomach and intestine, 

 and a subsequent resynthesis of the digestion products into the tissue and cell sub- 

 stances of the body. 



Bainbridge^ and Sperry and Rettger^ demonstrated that not even the most active- 

 ly proteolytic aerobes and anaerobes are able to attack native proteins when deprived 

 of accompanying enzymes and when the proteins are the only possible source of ni- 

 trogen. Sperry and Rettger employed crystallized egg albumin and edestin, in a me- 

 dium which furnished all of the other necessary food substances. The addition of a very 

 small amount of commercial peptone (mere traces) was sufficient to initiate growth and 

 the elaboration of proteolytic enzyme which then reduced the peptone to simple 

 products. 



Berman and Rettger^ demonstrated, further, that proteoses likewise are not di- 

 rectly available to the bacterial cell, and that they and the higher polypeptides at 

 least must first be hydrolyzed by proteolytic or peptolytic enzymes before they are 

 made available. They also showed that many bacteria do not produce the enzymes 

 necessary for preparing proteoses and the higher polypeptides for use, and that these 

 are therefore not utilized at all by these organisms. Bad. coli is one of this group. 



According to E. Fisher and others protein is a complex aggregate of amino acids. 

 By the use of strong sulphuric or hydrochloric acid, barium hydrate, superheated 

 steam, or of proteolytic enzymes, these structural units can be broken loose from their 

 combinations, and thus be identified by appropriate methods as individual amino 

 acids. 



Besides the numerous monoamino, mono-, and di-carboxylic acids, and the hetero- 

 cyclic acids (tryptophane, proline, histidine, etc.), two well-known diamino-mono- 

 carboxylic acids have been isolated from proteins : arginine and lysine. 



The molecular weight of protein is claimed by some to be at least 15,000-18,000. 

 If the entire protein molecule were made up of amino acids of the average molecular 

 size of alanine (CH^-CH'NHj-COOH), it would be a composite of well over 150 in- 

 dividual amino acids or amino acid units. One hundred per cent recovery of amino 

 acids from the protein molecule has not been made. Osborne^ derived amino acids from 



' Abderhalden, E.: Cetitralbl.f. BaktcrioL, Abt. II, 37, 280. 1913. 



* Bainbridge, F. A.: /. Hyg., 11,341. 1911. 



3 Sperry, J. A., and Rettger, L. F.: /. Biol. Chem., 20, 445. 1915. 



1 Berman, N., and Rettger, L. F.: J. Bad., 3, 367. 19 18. 



s Osborne, T. H.: Tlie Vegetable Proteins. London: Longmans, Green & Co., 1909. 



