14 



INTERMEDIARY METABOLISM AND GROWTH 



HOOC CH3 



^ +H 



DPN 



DPNH 



Fig. 4. Mechanism of oxidation of DPN* by lactic acid. 



Let us now consider the acyl dehydrogenases and succinic dehydrogenase 

 enzymes which have been purified from mitochondria. It has been ascertained 

 that at least three acyl dehydrogenases exist. These are the G, Yj, and Y2 enzymes 

 (Crane et aL, 1956). The G enzyme is a cuproflavoprotein. The Yj and Yj flavo- 

 proteins contain small amounts of iron (Table 2). 



The mechanism of dehydrogenation is shown in Fig. 5. It is to be noted that 

 both of the hydrogen atoms are transferred from the substrate to the FAD portion 

 of the dehydrogenase. Presumably, the metal component of the enzyme mediates 



OPOaHj 



FMN 



+ 2H 



CH; 



CH 



FMNHa 

 Fig. 5. Oxidized and reduced forms of flavin mononucleotide. 



