ENZYME COMPLEXES 



from the "closed" enzyme in appearance and composition, is 

 now capable of catalyzing the two reactions involving cyto- 

 chrome c just described. The "open" or "closed" enzyme of 

 molecular weight of approximately 2,000,000 (lipid free) contains 

 flavin, non-heme iron, copper, a hematin component spectro- 

 scopically indistinguishable from cytochrome b, and one indis- 

 tinguishable from the heme component of cytochrome oxidase. 

 On treatment of this preparation with trypsin two fractions may 

 be obtained. One (A Fraction) contains flavin, the bulk of the 

 iron, and the cytochrome b, and catalyzes the antimycin- 

 sensitive reduction of cytochrome c. The other (B Fraction) 



CYT C C IN THE OPEN PREP) 



jl I \ 'CYTOCHROME b" \ \ \ \ *CYTOCHROME OXIDASE' 



DPNH- 



FLAVIN _J_Fe — -♦Fe 



F»-PORPJH 



» Fe_.^CU('). 



Fa-PORPH 



,CUf?)_02 



CLOSED PREPARATION 

 TRYPTIC DIGEST, A FRACTION m\ |^TRYPTIC DIGEST, B FRACTION^ 



■ DPNH-CYT 

 REDUCTASE 



KDIAPHORASE-H 



Figure 2. 



contains the remaining iron, the enzyme-bound copper, and the 

 heme component of cytochrome oxidase. It functions only as a 

 cytochrome c oxidase. Further modification of the antimycin- 

 sensitive, hematin-containing cytochrome reductase leads to the 

 isolated ferroflavoprotein DPNH-cytochrome reductase, whose 

 relationship to diaphorase had already been established (27). 

 Thus we can achieve the complete and continuous transformation 

 of a mitochondrial electron transport enzyme into isolated, 

 soluble electron transport enzymes of any desired degree of 

 complexity. This transformation is then "closed" — » "open" 

 — > hemometalloflavoprotein -^ metalloflavoprotein -^ flavo- 

 protein. The different preparations and their properties may 

 be pictured as in Figure 2. 



263 



