230 UTILIZATION OF CARBOHYDRATES 



cultural media in which bacteria are growing affects the character of the products they 

 form very strikingly. In general, it may be said that utilizable carbohydrate protects 

 protein from direct bacterial utilization for energy. On the other hand, it must not 

 be forgotten that, under certain circumstances, the addition of utilizable carbohydrate 

 may indirectly bring about some alteration in the protein constituents of cultural 

 media which might not otherwise take place. 



Thus, it appears to be a fact that utilizable carbohydrate, added to cultures of the 

 gas bacillus {Bacillus welchii), indirectly leads to the appearance of a histamine-like 

 substance, which is not produced by the action of the organism upon the protein 

 constituents when carbohydrate is absent. ' It seems not improbable that the organ- 

 ism produces an enzyme, of the nature of a carboxylase, which acts upon histidine, 

 or possibly a histidine peptide, in accordance with the equation : 



H— C — NH H— C — NH 



II />C-H II ^C-H 



I (Carboxylase) | +CO2 



CH. CH, 



I I 



CH • NH. CH. . NH, 



I 

 COOH 



(Histidine) (Histamine) 



Only very small amounts of this histamine-like substance are produced in ordinary 

 cultural media, but it is very reactive chemically. One part in five million may cause 

 a very definite contraction in a piece of isolated surviving smooth muscle from a 

 guinea pig.^ 



The observations of Koessler and Hanke^ suggest that a somewhat similar reaction 

 may occur among certain strains of other common bacteria. Finally, it must be borne 

 in mind that "resting" bacteria, i.e., actively growing bacteria washed free from 

 cultural medium, and suspended in non-nutritive, isotonic solutions containing ap- 

 propriate amounts of test substance, can and do bring about chemical changes that 

 do not necessarily take place when the organisms are growing freely. Thus, many 

 "resting" bacteria will change methyl glyoxal to lactic acid, although this reaction 

 does not seem to take place under conditions where the microbes are growing freely. 

 Quastel and his associates^ have made several important studies upon this significant, 

 but little studied, aspect of bacterial metabolism. 



CARBOHYDRATES AND THE STRUCTURAL REQUIREMENTS OF BACTERIA 

 CELL CONSTITUENTS 



The predominance of nuclein compounds in bacteria, described by many investi- 

 gators, focuses attention upon the nature of the carbohydrate component. Bendix,^ 



I Kendall, A. I., and Schmitt, O. F.; J. Infect. Dis., 39, 250. 1926. 

 ^ Guggenheim, M.: Die biogene Amine (II. Aufl.) 1923. 

 ^Koessler, K. K., and Hanke, M.: /. Biol. Chem., 50, 131. 1922. 

 4 Quastel, J., et al.: Biocliem J. 1924-27. (Numerous articles). 

 sBendix, E.: Deutsche med. Wchnschr., 27, 18. 1900 



