Alternative Pathways of Electron Transport 197 



electrons and the system of the phosphorylation enzymes 

 involved are intact and unaffected by the vitamin deficiency. 

 But with p-hydroxybutyrate as substrate the P/0 ratios are 

 lower than in normal mitochondria, and even lower than with 

 succinate and the same mitochondria. This disturbance, 

 which in vitro can be overcome by the addition of vitamin K^, 

 can only be explained by assuming that there is a gap in the 

 normal phosphorylating pathway; the gap must be between 

 the pyridine nucleotides and cytochrome b, for from there, as 

 the experiments with succinate show, the electron transport 



Table I 



Oxidative phosphorylation in vitamin K-free chicken liver 

 \xatom oxygen \xatom phosphorus PjO 



is quite normally linked with phosphorylation. Obviously the 

 hydrogen atoms or electrons coming from the reduced pyridine 

 nucleotides must circumvent this gap, i.e. they must make 

 their way via the cytochrome c reductase. Entering the 

 phosphorylating pathway at the cytochrome c level, they can 

 bring about only one single phosphorylation. Similar con- 

 clusions have recently been drawn from experiments with 

 irradiated mitochondria (Beyer, 1958), and in bacterial 

 systems, also, vitamin K is necessary for electron transport 

 and phosphorylation, as has been shown by Brodie, Weber 

 and Gray (1957). 



Thus, it appears that the scheme postulated in 1954 is now 

 well enough established and we may consider what conclusions 

 can be drawn from it. First of all, if two different pathways, 



