16 1. MALONATE 



1956; Singer, et al., 1957; Green and Crane, 1958; Singer and Lara, 1957; 

 Green and Flieseher 1960; Green, 1960; Redfearn, 1960). The particulate elec- 

 tron transport particle (ETP) of Green, obtained from heart mitochondria, is 

 a succinate oxidase preparation and has been shown to contain the following 

 components (per molecular weight of about 5 x 10^): flavin dinucleotide 2, 

 nonheme iron 64, heme (equal amounts of cytochrome a, cytochrome 

 b, and cytochromes c + Cj) 6, copper 8, ubiquinone (coenzyme Q) 10, and 

 lipid 34,5%. In addition, there are the several proteins with which these 

 substances are bound. Such preparations also oxidize NADH, ascorbate, 

 p-phenylenediamine, and hydroquinones, these substrates supplying elec- 

 trons at various sites in the electron transport chain. The use of various 

 electron donors and acceptors, the application of specific inhibitors, and the 

 fragmentation of the succinate oxidase complex have led to several postu- 

 lates of the pathways of electron flow. One difficulty is the probable dif- 

 ference in pathways between mitochondrial phosphorylating systems and 

 submitochondrial nonphosphorylating preparations. A second difficulty is 

 the possibility of alternate pathways of electron flow rather than a single lin- 

 ear sequence. Scheme 1-2, (Green, 1960; Redfearn, 1960) might be assumed 

 provisionally: 



UQ UQ 



cs . i'«/ ^ ^^ ^ ^^f,| 



Succinate »- ASF ^ -• NADH 



iFe) \^ /^ I >\ ^ lFe\ 



(1-2) 



Fe represents nonheme iron, f, is the flavoprotein associated with succinate 

 dehydrogenase, f^ is the flavoprotein associated with NADH dehydrogenase, 

 UQ is ubiquinone (coenzyme Q), ASF is the antimycin-sensitive factor, and 

 the other symbols indicate the usual cytochromes. It is possible that cyto- 

 chrome b and ubiquinone are common to the two pathways from succinate 

 and NADH, but Green believes the evidence points to fusion of the chains 



