HENRY R. MAHLER 



transport from these dehydrogenases to the cytochrome system. 

 This enzyme utiHzes enzyme-bound reduced FAD (of the de- 

 hydrogenase) as substrate and a cytochrome (cytochrome c is 

 the one actually employed) as electron acceptor. Although it 

 had been shown previously that an enzyme-bound electron 

 transport coenzyme (i.e., the DPNH of D-glyceraldehyde phos- 

 phate dehydrogenase) could become the substrate or coenzyme 

 for a second enzyme (8,26), this novel reaction marks the first 

 such in the flavin field, is the first obligatory case, and provides 

 us with yet another possible pathway between the flavoprotein 

 and cytochrome systems. There is considerable evidence that 

 the three acyl CoA dehydrogenases (one specific for the lower 

 fatty acids — the green copper-containing butyryl CoA dehydro- 

 genase — and two yellow, iron-containing, more general acyl 

 CoA dehydrogenases) and ETF originally formed part of a more 

 elaborate enzyme complex (3). Within this complex the copper 

 associated with the isolated butyryl CoA dehydrogenase may 

 have been used to bind the four components by complex forma- 

 tion and to provide the link between this complex flavoprotein 

 and the cytochrome system. 



DPNH Oxidase 



The most complicated, well-defined enzyme complex 

 which has been subjected to investigation is the DPNH oxidase 

 complex isolated by Green et al. (17) and exhaustively studied by 

 Mackler (24,25). This particulate enzyme can be obtained in a 

 highly purified, highly active form and then carries out only the 

 antimycin-sensitive reaction DPNH -f H+ + V2 0-2^ DPN+ + 

 H2O. In this state the enzyme apparently contains but little 

 cytochrome c, and does not catalyze either the reduction of ferri- 

 cytochrome c by DPNH or the oxidation of ferrocytochrome c 

 by oxygen. On prolonged standing or on treatment of this 

 "closed" enzyme by deoxycholate or other surface-active agents, 

 the ability to catalyze the aerobic oxidation of DPNH by O2 

 disappears. In its stead, this "open" enzyme, indistinguishable 



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