PROBLEMS OF METHOD 203 



pounds as having "high energy" phosphate bonds is ambiguous (103). 



In general, most of the oxidative phosphorylations associated with 

 glucose or other substrate oxidations are carried out at the cofactor 

 level; electrons from substrate are passed along a chain of respiratory 

 carriers to oxygen and in the process, in ways still unknown in detail, 

 the energy released in electron transfer is used to form ATP. Sub- 

 strate-level phosphorylations occur in the anaerobic conversion of 

 glucose to ethanol and carbon dioxide — the Embden-Meyerhof path- 

 way — and, possibly, in the oxidative decarboxylation of a-ketoglutaric 

 acid. 



As described briefly in Chapter 9, fungi during growth transform 

 inorganic into organic phosphate. Organic phosphorus compounds 

 which have been identified in fungi and actinomycetes include sugar 

 phosphates (38, 94, 134), adenosine phosphates (9, 162, 219), and 

 various of the other known nucleotides (9). A mycelial extract of 

 Rhizopus nigricans has myokinase activity (228), catalyzing the re- 

 versible transphosphorylation: 



2 adenosine diphosphate ^± adenosinetri phosphate + 



adenosinemonophosphate (1) 



The utilization of ATP to phosphorylate organic molecules is im- 

 plicit in the two major respiratory pathways for glucose, both of which 

 start with glucose-6-phosphate. There is very suggestive evidence that 

 ATP generated by oxidative processes is involved in the streaming of 

 the myxomycete Physarum polycephalum as it is in muscular con- 

 traction (3, 177, 303, 304, 305). 



1. PROBLEMS OF METHOD 



The respiration of whole cells and of extracts is usually measurable 

 in terms of gas exchange — oxygen uptake or carbon dioxide formation. 

 The basic instrument in most laboratories is the Warburg-Barcroft 

 constant-volume manometer, described in the manuals of Dixon (77) 

 and Umbreit et al. (308). Macrorespirometers with larger capacity 

 have been designed (170, 188, 282, 328), and a few studies on fungi 

 have been performed with more sensitive manometric apparatus (78, 

 214, 324). An amperometric procedure for measuring oxygen utiliza- 

 tion has been applied successfully in studies on Penicillium chryso- 

 genum (52). 



Dye reduction methods have a more limited application but are 

 useful in some problems. The best known is that of Thunberg (298), 



