372 VIII. IIEMATIN ENZYMES, I. CYTOCHROME SYSTEM 



and that the inhibitors react with the respiratory enzyme; thus Warburg 

 (2925) measured what he assumed to be the photochemical absorption spec- 

 trum of the respiratory ferment of rat retina by the effect of carbon monoxide 

 in the dark and under illumination on glycolysis. 



Later, however, evidence for different effects of oxygen pressure and of 

 inhibitors on respiration and Pasteur effects of certain tissues were discovered 

 and a separate catalyst of the Pasteur reaction, the "Pasteur enzyme," was 

 assumed. In fact, Warburg himself had noted as early as IQ-^G {2918) that 

 carbylamine inhibited the Pasteur effect without inhibiting respiration. The 

 same was found for carbon monoxide in rat retina by Laser (IGoJ^). Differ- 

 ences in oxygen affinity between respiratory enzyme and the assumed 

 catalyst of the Pasteur reaction have also been noted by several authors {379, 

 1512,16-53). In general the respiratory ferment has a greater affinity for 

 oxygen and a smaller one for carbon monoxide than the Pasteur enzyme in 

 most tissues of higher animals, while for bacteria and for human myelocytes 

 the reverse holds (1509-1512). For bone marrow (in both phosphate and 

 bicarbonate medium) and for brain cortex and retina in phosphate (not in 

 bicarbonate) medium, however, the changes in respiration and lactic acid 

 fermentation produced by low oxygen tension and by carbon monoxide were 

 always found reciprocal (509,2961,2962). The evidence from the inhibition 

 experiments for a Pasteur enzyme distinct from the respiratory enzyme 

 cannot, therefore, be considered conclusive. 



The difficulties encountered in such inhibition experiments will be dis- 

 cussed in Section 5.4. GaflFron (972) has pointed out that the inhibition of 

 the Pasteur enzyme by oxygen resembles the oxygen inhibition of hydro- 

 genase. 



More recently Stern and Melnick (1907-1909,2660) have tried to solve 

 the problem by comparing the photochemical absorption spectrum of both 

 respiratory ferment and Pasteur enzyme of yeast on the one hand, and of 

 mammalian tissue on the other. The respiration of rat retina is not inhibited 

 by carbon monoxide, and hence the photochemical absorption spectrum of 

 the respiratory enzyme in retina cannot be determined. The spectrum of 

 the respiratory ferment of rat heart was thei^fore used for comparison with 

 that of the Pasteur enzyme of rat retina. All these spectra show a weak 

 band in the yellow-green, a still weaker one in the blue-green region, and a 

 strong Soret band. No differences between the absorption spectra of Pasteur 

 enzyme and respiratory enzyme were found with regard to the Soret band 

 (430 m^ in yeast, 4.J0 m/x in rat tissues) and the weak band in the blue-green 

 (510 mM in both yeast and rat tissues). Small differences in the height of 

 absorption of the enzymes of yeast at 500 m/i were found, and a distinct 

 difference in the position of the first absorption band in rat tissues (respiratory 

 enzyme of rat heart, 589 mn; Pasteur enzyme of rat retina, 578 m;u). In view 

 of the fact that the last-mentioned difference was found for enzymes from 

 different tissues, and particularly in view of the great technical difficulties of 

 such experiments and the low sensitivity in the visible part of the spectrum, 

 we cannot consider these small differences of weak absorption bands as con- 

 clusive evidence for a difference between Pasteur enzyme and respiratory 

 ferment. 



