RESPIRATORY FERMENT AND RELATED CYTOCHROMES 363 



absorption coefficient, /3, is given by Warburg as: 



(1/c/) In (///o) 



with c in gram moles per gram; it must be multiplied by 2.3 X 10"^ 

 in order to transform it to e^yi, the unit used in this book. If this is 

 done, the values are of the size usually found for hematin compounds. 

 The concentrations of the catalyst is very small (10^ M). 



The photochemical spectrum of rat heart muscle oxidase was 

 studied by Melnick {1907,1909} using succinate as substrate. The 

 first absorption band (589 m/x) was found in a position close to that 

 of the yeast oxidase, but the Soret band was found at 450 m/x. 

 Another weak band at 510 m/i was observed. 



While these results leave no doubt that these catalysts are hematin 

 compounds of a nature somewhat different from that of protohematin, it must 

 not be forgotten that the evidence is purely spectroscopic. The spectra sug- 

 gest that the hematin is derived from a porphyrin with one or more carbonyl 

 groups in the side chains. Not even this can be considered definitely proved. 

 The unexpected spectra of the verdoperoxidase (Chapter IX, Section 3.6.), 

 although not very similar to that of the respiratory ferment, are a warning 

 that we do not yet know all types of hematin compounds. The reader should 

 also refer to what has been said about "green" and "green-red" hemins in 

 Chapter V. To draw conclusions from the spectrum as to the nature of 

 these side chains, whether, for example, they are formyl or acetyl, or as to 

 their position, is impossible ; this should be clear, particularly if one remembers 

 that the unknown protein bearer certainly has an influence on the spectrum. 



3.6.2. Inhibitors. The distribution constant, K, of the respiratory 

 ferment of yeast and acetic acid bacteria was found to be about 9. 

 If this value is compared with the K of hemoglobin (0.01), it is seen 

 that the relative affinity of the respiratory ferment for carbon monox- 

 ide is much smaller than that of hemoglobin. The toxicity of carbon 

 monoxide for vertebrates is thus due to its combination with hemo- 

 globin, not to its interference with tissue respiration. 



Cyanide of the concentration 10 * M inhibits the respiratory fer- 

 ment completely.* In contrast to the inhibition by carbon monoxide, 

 that by cyanide was found by Warburg to be independent of oxygen 

 pressure {2920). Warburg explained this by assuming that only the 



* In contrast to ferricytochrome c, hemoglobin, and other hematin compounds, 

 cytochrome oxidase combines with undissociated hydrocyanic acid and hydrazoic acid, 

 not with cyanide and azide ions; this was recently discovered by Stannard and Horecker 



{ism). 



