HYDROGEN-ION CONCENTRATION 



161 



to make a trace of growth in an alkaline medium, the carbon dioxide 

 produced will lower the pH. Organic acids may also be produced. Car- 

 bon dioxide from the air will be absorbed by alkaline media. 



0.08 



c 



"e 



t 0.06 



0) 



0) 



a. 



■I 0.04 



_>i 



2 



•o 

 >« 



o 



% 0.02 



•a 

 m 



a. 



7 

 pH 



Fig. 25. 



of urea 



25. The shift of optimum pH for urease activity due to change in concentration 

 sa. (Courtesy of \'an Slyke, Advances in Enzymol. 2: 41, 1942. Pubhshed by 



permission of Interscience Publishers, Inc.) 



pH 

 Pig. 26. The effect of pH on the rate of linear growth of Neurospora crmsKi. 

 tesy of Ryan, Beadle, and Tatum, Am. Jour. Botany 30: 790, 1943.) 



(0,11. 1 V 



It was pointed out in Chap. 4 that pH affects the activity of a.i/jymes. 

 In general, there is a striking correlation between the optimum pH range 

 for most enzymes and the optimum pH range for gro^vth. In a survey 

 of the literature Haldane (1930) found all but 9 of 105 enzymes to have 

 optima between pH 4 and 8. Most fungi have pH optima for growth 



