FACTORS IN RESPIRATION 



209 



Figure 3. The effect of oxygen 

 pressure on the rate of respiration 

 of Aspergillus niger. Redrawn 

 from P. Shu, Journal of Agricul- 

 tural and Food Chemistry, Vol. 1, 

 p. 1119, November 25, 1953. Copy- 

 right 1953 by the American 

 Chemical Society and reprinted 

 by permission of the copyright 

 owner. 



400 

 Oxygen pressure, mm Hg 



800 



259, 260, 291). Respiration depends immediately upon dissolved oxy- 

 gen, which in turn is proportional to the partial pressure of oxygen 

 in the gas phase. Finn (83) defines C crit as the concentration of dis- 

 solved oxygen above which cell respiration is independent of the 

 oxygen concentration; data from several sources show that C crit for 

 Penicillium chrysogenum is about 0.022 millimoles per liter (equiva- 

 lent to an oxygen tension of 16 mm of mercury), that for yeast and 

 Escherichia coli considerably lower. Amperometric measurements 

 show that the rate of oxygen utilization is independent of oxygen 

 pressure down to very low values (52). It follows, therefore, that the 

 requirement of many fungi, e.g., Aspergillus niger (Figure 3), for rela- 

 tively high oxygen pressure for maximal respiratory rate means that 

 other factors must be operative. Studies on the respiration of my- 

 celium of Myrothecium verrucaria indicate that the rate of oxygen con- 

 sumption by these rather active cells is limited in part by the rate 

 at which oxygen reaches the interior of the cell mass (70). 



The oxygen uptake of Micromonospora vulgaris is reduced by high 

 oxygen pressure (315), but this effect is not usually encountered in the 

 fungi. 



Little evidence is available on the influence of carbon dioxide pres- 

 sure on fungus respiration. Most respirometric techniques involve 

 removal of metabolic carbon dioxide during measurement of oxygen 

 uptake. In many bacteria oxygen uptake is in fact depressed by such 

 removal of carbon dioxide (119). Two methods are available to deter- 

 mine if this occurs with any given organism: use of Warburg's "in- 

 direct" method (308) or use of diethanolamine as a carbon dioxide 

 "buffer" (166, 231). 



Nutrients. Potassium, phosphorus, and magnesium are usually sup- 

 plied to respiring cells, although it is likely that endogenous reserves 



