94 BACTERIOLOGICAL CHEMISTRY 



in this way the amount of enzyme could be easily deter- 

 mined. It was found that the presence of glucose in an 

 agar-peptone medium stimulated the production of urease 

 but depressed that of catalase. The presence of urea 

 did not stimulate urease production nor did succinate or 

 fumarate stimulate fumarase production, which is high 

 in the presence of glucose. Quastel considers that the 

 effect of the substrate on enzyme production depends on 

 a balance of factors : (a) whether the substrate tends to 

 destroy the enzyme or to protect it from destruction 

 (j)erhaps by forming a reversible complex with it), and 

 (b) whether the substrate has an effect on the synthesis 

 of the enzyme by contributing some necessary molecules 

 or configuration for that synthesis. 



Another type of enzyme which is adaptive is the 

 hydrogenlyase, produced by the coli group of organisms 

 when grown in the presence of formate, and which breaks 

 formic acid down to carbon dioxide and hydrogen : — 



HCOOH > H2 + CO2. 



It is also produced in presence of glucose or glycerol, 

 which yield formic acid as a result of their fermentation. 

 Some specific factor in the medium also appears to be 

 necessary since, generally speaking, the enzyme is only 

 produced when the organism is grown on a tryptic digest 

 of casein. If the bacterium is grown on synthetic media, 

 even one containing formate, no hydrogenlyase is pro- 

 duced in spite of good growth. It is almost certain that 

 in this case the enzyme is not produced as a result of 

 selection of a mutant strain, since the addition of formate 

 to a young growing culture on tryptic casein digest 

 caused the appearance of the enzyme in less than an hour, 

 during which time the number of organisms had increased 

 by only 18 per cent. A maximum production of enzyme 

 occurred in two hours with an increase of the viable 

 count by 34 per cent. In other words a maximum 

 production of hydrogenlyase had occurred before the 



