208 



RESPIRATION 



appears also to require the formation of inducible enzymes (127). In 

 Streptomyces coelicolor gluconic acid and pentoses are oxidized only 

 by specifically adapted cells (66). In none of these cases just cited, 

 however, has the specific enzyme been isolated and studied as such. 



Acidity and Respiration. In most experiments reported, the pH 

 of the suspending medium has little effect on endogenous metabolism 

 over the range pH 5 to 8 (3, 70, 187), and the data of Figure 2 are 

 typical of many. Exceptions to this general rule have, however, occa- 

 sionally been found (93, 127, 214). Acidity is more apt to be important 

 in substrate respiration, e.g., the oxidation of phenylacetic acid by 

 Penicillium chrysogenum (135) and of glucose by Streptomyces griseus 

 (134). Since the internal pH of the intact cell is probably protected 

 against all but the most extreme changes in the medium, it seems likely 

 that pronounced pH effects on respiration of undissociated compounds 

 or of very weak acids signify that surface-located enzymes are involved 

 in the total process of metabolism. 



Phosphate buffers are the most generally satisfactory for respiro- 

 metric studies; others, particularly acetate, are often toxic (Chapter 1). 



Temperature. Most respirometric studies of saprophytic fungi and 

 actinomycetes are performed at moderate temperature, 20-30°C; 

 higher temperatures are more suitable for the fungi pathogenic to 

 animals (215). Carbon dioxide evolution from growing mycelium of 

 Aspergillus niger has a high Q 10 at low temperature, e.g., 312 over the 

 range 7-17°; the Q 10 drops as the temperature is raised, and is only 1.7 

 over the range 27-37° (217). 



Oxygen and Carbon Dioxide Pressure. The response of aerobic 

 respiration to oxygen pressure varies with the organism studied (3, 72, 



Figure 2. pH and the endo- 

 genous respiration of Strepto- 

 myces coelicolor (curve 1), My- 

 rothecium verrucaria (curve 2) 

 and Fusarium solani (curve 3) 

 mycelium. 



