196 C. Martius 



effect. This is an important fact, for it demonstrates that in 

 the case of vitamin K we are really dealing with the physio- 

 logical substrate of this enzyme. 



Another important property of vitamin K reductase is its 

 high activity. In low concentrations and with phylloquinone 

 as acceptor this enzyme shows a turnover number of about 

 1,200,000 per molecule per minute. This calculation is based 

 on the flavine content. The molecular weight is not yet 

 known with certainty. The sedimentation coefficient (S20) is 

 very low, about 3 • 1 . Unfortunately we have not yet been able 

 to estimate the diffusion coefficient. Assuming that the 

 molecule has a globular shape, the molecular weight would be 

 in the region of 30,000. 



Though values for the content of cytochrome c reductase are 

 known only for pig heart, the concentration in the tissues of 

 both enzymes seems to be of the same order of magnitude. 

 This fact, together with the above-mentioned high turnover 

 number of vitamin K reductase, points to the important role 

 of this enzyme in cell respiration. A further peculiarity of 

 vitamin K reductase is the fact that it is not only reduced by 

 reduced diphosphopyridine nucleotide (DPNH), but also by 

 reduced triphosphopyridine nucleotide (TPNH) (Martius and 

 Marki, 1957), which implies that TPNH could also contribute 

 to the formation of high-energy phosphate bonds to the same 

 extent that DPNH does. This would not be in agreement with 

 the recent statements by Vignais and co-workers (Vignais and 

 Vignais, 1957; Vignais, Vignais and Bartley, 1957). However, 

 the whole problem remains open and should be carefully 

 reinvestigated. 



We have recently carried out a simple experiment which is 

 really a repetition, with better facilities, of an older experi- 

 ment of ours. Using liver mitochondria from highly vitamin 

 K-deficient chickens we have compared the P/0 ratios which 

 one obtains with p -hydroxy butyrate and with succinate as 

 hydrogen donors (Table I). In the latter case quite normal 

 values are obtained, which seem to indicate that for steps (2) 

 and (3) of the phosphorylation sequence the pathway for the 



