272 EXISTENCE OF A REDUCING ENDO-ENZYME 



In regard to its sensitiveness towards alcohol, reductase 

 is in marked contrast with glycogenase, which can be obtained 

 in an active state even from livers which have been for months 

 under alcohol. This power that colloids have of protecting 

 enzymes is a well-known property of the relationship between 

 these two classes of bodies. 



As judged by the criterion of solubility, reductase is 

 comparatively insoluble; it will not, for instance, dialyze away 

 from the cell-proteins. But in that it can in some measure 

 pass into solution in dilute glycerol, it cannot be regarded as 

 entirely of an insoluble nature 



The insoluble endo-enzyme is now fully recognized. 

 Professor Adrian Brown tells me that phyto-enzymes of a non- 

 soluble order exist, and according to Vernon( 22 )the oxidase of 

 the liver is insoluble. He adds that its insolubility does not 

 preclude its enzymic nature, as there is a good deal of evidence 

 pointing to a similar property in some lipolytic enzymes. 



VIII. REMARKS ON TISSUE RESPIRATORY FERMENTS. 



Besides reductase, at least two other types of respiratory 

 enzyme exist in the liver, to confine our attention only to the 

 liver in the meantime, namely a catalase and an oxidase or a 

 number of oxidases. A catalase has long been recognised in 

 the blood and tissues; Creighton and I ( 25 ) recently wrote: 



"The existence of a catalytic enzyme in the mammalian 

 liver is fully confirmed. The decomposition of H 2 2 is effected 

 by this enzyme, and is not due to the presence of proteins or 

 other organic matter in the press-juice." 



Boiled juice gives rise to no decomposition of H 2 2 ; and 

 the amount of H 2 O 2 decomposed bears no relation at all to the 

 amount of protein in the juice, for a few drops of a very dilute 

 juice reduced 97.2% of H 2 O 2 in the first five minutes. No 

 doubt it is possible that the two enzymes, catalase and reduc- 

 tase, may co-operate in hepatic reductions. 



