The Protein-Sparing Action of Utilizable Carbohydrates in Cultures of Certain Sugar-Fermenting Organisms

Attention often has been called to the effect of the presence of various sugars on the protein metabolism of bacteria. It is a well-known fact that in cultures of certain organisms in the ordinary sugar-protein media, indol is not formed, gelatin is not liquefied, casein is not digested, and ammonia-production is greatly lessened. Inasmuch as the decomposition of a carbohydrate is accompanied by the formation of more or less acid, and because the protein changes mentioned are commonly regarded as due to the action of one or more trypsin-like enzymes?that is, enzymes which do not act in acid media ?some investigators have inclined to the belief that it is the acid resulting from the decomposition of the sugar, not the mere presence of the sugar itself, which alters the normal progress of the protein changes.