PASTEUR ENZYME 371 



of Azotohader has the properties expected for a respiratory ferment. 

 Carbon monoxide shifts the absorption band to 634 m^, oxygen to 

 645 m/i, while aeration in the presence of cyanide causes the band to 

 disappear. This cytochrome is thus autoxidizable and reacts with 

 carbon monoxide and cyanide. Pyridine produces a hemochrome 

 with a band at 625 mju and a weaker band at 600-605 m/x, both rather 

 diffuse (Roche, 2307). The hematin is thus certainly not a porphyrin 

 hematin. 



Lemberg and Wyndham (1716) have pointed out that cytochrome 3.2 

 resembles certain bile pigment hemochromes in its spectroscopic behavior. 

 These hemochromes were obtained by introducing iron into biliviolinoid bile 

 pigments, followed by combination with pyridine. They are spectroscopically 

 quite different from verdohemochromes {cf. Chapter X) and should not be 

 called such. Carbon monoxide and oxygen shift their absorption bands 

 toward the red like those of cytochrome a2, and ammonium sulfide causes the 

 disappearance of the band in the orange; the same has been reported for 

 cytochrome aj. 



Cytochrome 3,2 in crushed Escherichia coli cannot oxidize cytochrome c, 

 but cytochrome c does not occur in E. coli mS4^). It would be of great 

 interest to study the photochemical absorption spectrum of Azotohader, in 

 which cytochrome a.o prevails. The fact stressed by Keilin that respiratory 

 activity of various microorganisms is not proportional to the cytochrome 

 content is no serious objection to such a role of cytochrome sa as a respiratory 

 catalyst, since the organism may contain varying amounts of cytochrome ai 

 in addition to a2, and both may be respiratory catalysts; secondly the dehydro- 

 genases may not have reached their maximum activity under the experimental 

 conditons. 



4. "PASTEUR ENZYME" 



In 1879 Pasteur discovered that under aerobic conditions the alcoholic 

 fermentation of yeast proceeds far less vigorously than under anaerobic con- 

 ditions [2110). The same was found later to hold for the lactic acid fermen- 

 tation {glycolysis) of many tissues. This suppression of the fermentation 

 processes by aerobiosis is called the Pasteur effect. Its purpose is evidently 

 to keep in check the substrate-wasting fermentation processes when substrate- 

 saving oxidation of glucose can be performed. 



We cannot here discuss fully the problem of the mechanism of the Pasteur 

 effect. The reader is referred to the papers of Burk {S81) and of Lipmann 

 {1758) and the discussion of these papers in the symposium. The earlier 

 hypothesis of Meyerhof which assumes aerobic resynthesis of glucose, had 

 to be abandoned. It is still not certain whether the effect is due to higher 

 oxygen pressure or to respiration. 



The Pasteur effect is inhibited by substances which also inhibit respiration; 

 carbon monoxide for instance causes an inhibition abolished by light {1654, 

 2920). It was therefore assumed that the Pasteur effect is due to respiration 



