230 RESPIRATION 



chromes are the same as those of yeast, and to be content with the 

 generalization that cytochromes are generally present in fungi. The 

 cytochrome c of Ustilago sphaerogena, for example, has a spectrum 

 like beef heart cytochrome c, but has a higher molecular weight and 

 a lower isoelectric point (208). In this organism, too, the conditions 

 of culture, especially the supply of zinc and of thiamine, markedly 

 affect the concentrations of the cytochromes (117). 



Exogenously supplied cytochrome, from animal sources, functions 

 as an electron carrier for the aerobic lactic dehydrogenase of Penicil- 

 lium chrysogenum (50) and for the succinoxidase systems of all forms 

 tested (13, 190, 258). 



Cytochrome oxidase may be assayed either manometrically or 

 spectrophotometrically (Figure 6), usually with animal cytochrome c 

 as substrate. The enzyme, operationally denned by these assays, seems 

 to be of universal occurrence in the fungi; experiments have covered 

 representatives of all of the major taxonomic groups (31, 32, 33, 46, 47, 

 57, 71, 117, 213, 230, 300). As in other organisms, cytochrome oxidase 

 activity is associated with the insoluble and sedimentable fraction of 

 homogenates (57, 71, 122, 258, 299). In bacteria, this fraction is 

 apparently the cytoplasmic membrane or a similar structure (266). 



The flavin components of the terminal system which proceeds over 

 the cytochromes (Equation 16) have not been systematically in- 

 vestigated. Reductases linking cytochrome c with the pyridine nu- 

 cleotide coenzymes and with succinate occur in Neurospora tetra- 

 sperma (57). 



a. 

 E 



o 



in 

 in 



C 

 Q> 



•o 



"75 

 <j 



'■*-» 



Q. 



O 



GO 



c 



sz 



10 



Time, minutes 



20 



Figure 6. Cytochrome oxidase 

 in Blastocladiella sp. Curve 1, 

 in presence of cyanide; curve 

 2, action of the enzyme. Re- 

 drawn, from E. C. Cantino, 

 "The Role of Metabolism and 

 alpha-Ketoglutarate Oxidase in 

 the Growth and Differentia- 

 tion of the Aquatic Phycomy- 

 cete, Blastocladiella Emer- 

 sonii," Transactions of The 

 New York Academy of Sciences, 

 Series II, Vol. 15, No. 5, p. 

 159-163 (1953), by permission 

 of the New York Academy of 

 Sciences. 



