THE NATURE OF ENZYME ACTION 297 



case, manganese and iron would be for them " co-enzymes," to 

 which we may now turn our attention. 



Co-enzymes 



It was noticed by Magnus that an extract of liver containing 

 lipase became inactive on dialysis. On investigation it was 

 found that the activity was restored by adding a portion of a 

 boiled extract of liver, or even a similar extract after proteins 

 had been precipitated by uranyl-acetate. The activating body 

 is soluble in absolute alcohol but not in ether, and is not present 

 in the ash of liver. It is, therefore, a non-colloidal substance, 

 but not inorganic. What may be called, then, the lipoclastic 

 system of the liver consists of two components — the one, 

 destroyed by boiling, may be regarded as the enzyme proper, 

 but it is inactive except in the presence of the dialysable body, 

 the " co-enzyme." 1 



A similar state of affairs has been shown by Harden and 

 Young to exist in the case of the alcoholic enzyme of yeast, 

 zymase. The press juice of yeast may be separated by dialysis, 

 or by filtration through gelatin, into two parts, each by itself 

 inactive, but becoming active when mixed. The filtrate or 

 dialysate always contains phosphates, and it was found that the 

 addition of phosphate to the inactive residue had a similar 

 activating effect to that of the filtrate itself. A remarkable fact 

 is that the amount of carbon dioxide (and alcohol) produced is 

 proportional to the amount of phosphate added — viz. one 

 molecule of carbon dioxide for each atom of phosphorus. The 

 authors are not prepared as yet to state whether phosphate is 

 the only co-enzyme concerned. 



Certain experiments of Cohnheim indicate that the pancreas 

 produces a co-enzyme for the glycolytic oxidase of muscle. 

 The difficulty in the investigation of this phenomenon is that 

 the pancreatic extract in 90 per cent, alcohol, which was 

 added to watery extracts of muscle, caused an inhibition of 

 sugar oxidation, if present even in slight excess. This may, 

 perhaps, be the reason why other observers have not been able 

 to confirm Cohnheim's results. The matter cannot be looked 

 upon as decided at present, but it appears from Cohnheim's 



1 According to recent work (Loevenhart, " Proc. Am. Physiolog. Soc," in 

 Amer. Journ. of Physiology, vol. xv. p. xxvii. 1906), the co-enzyme in this case is 

 bile salts. 



