254 



DANIEL M. ZIEGLER 



The turnover of the flavoprotein in CoQ reductase with CoQ as the 

 electron acceptor is shghtly faster than that of the same enzyme in the 

 electron transport particle (ETP) with any of the electron acceptors listed 

 in Table II. The calculated turnover of the succinic flavoprotein in ETP 

 is based on the assumption that all the flavin in the particle released by 

 acid only after tryptic digestion is part of the succinic dehydrogenase [4]. 

 Either this assumption is not valid or some activation of the enzyme occurs 

 during its isolation. 



The soluble succinic-CoQ reductase contains 4-2 to 4-6 m/^moles 

 flavin, 4-4 to 4-8 m/xmoles haem, 34 to 38 m^amoles non-haem iron, and 

 o- 18 to 0-20 mg. lipid per mg. protein. The ratio of flavin to protein in the 



TABLE II 



Turnover Rates* of the Succinic Flavoprotein in Soluble and Particulate 



Preparations 



Preparation 



Flavoprotein 



concn. 



(m/nmoles/mg. 



prot.) 



Electron acceptor 



CoQ 



Phenazine 

 methosulphate 



O, 



Primary 

 succinic 

 flavoprotein 



[4] 



Succinic CoQ 

 reductase [5] 



Electron 

 transport 

 particle [6] 



4-3 



4-2 



o- ig 



12 600 



4100 



II 300 



9 700 



* The turnover rates are expressed as moles of succinate oxidized per min. 

 per mole of succinic flavin. 



reductase is almost identical with that of the primary succinic flavoprotein 

 and both forms of the dehydrogenase contain non-haem iron. Singer and 

 his associates have reported that the ratio of iron to flavin in the primary 

 flavoprotein is 4 : i ; whereas in the reductase the ratio is 8:1. About one- 

 half of the non-haem iron can be removed from the reductase by prolonged 

 aerobic dialysis against 10 ~^ M ethylenediamine tetraacetate, but the CoQ 

 reductase activity of the enzyme is destroyed by this procedure. 



The iron that is removed by aerobic dialysis is probably not adventi- 

 tious iron since the enzyme can be dialyzed anaerobically for the same 

 length of time without the loss of either iron or activity. Addition of ferric 

 or ferrous ions to the enzyme after aerobic dialysis does not restore activity. 

 It is possible that some functional group (i.e. thiol) required for iron 

 binding is oxidized during prolonged aerobic dialysis. 



