ENZYMES AS SYNTHETIC AGENTS 493 



the activity of a catalyst of a different nature from the original 

 pepsin employed. 



Before proceeding to consider Robertson's theory as to 

 how these phenomena may best be correlated with theories 

 of enzyme catalysts, it will be well to consider critically the 

 validity of the evidence upon which the theory of enzyme 

 catalysis is to be extended to cover new phenomena. 



It is obvious that the statement that we are dealing in these 

 experiments with a reversible catalysis induced by enzymes 

 implies that we are satisfied with the evidence in reference to 

 two points. These are (i) that the body produced after con- 

 centration and addition of the enzyme is really " paranuclein A," 

 and identical with one of the original bodies hydrolysed ; (2) 

 that this body is actually produced in the solution as the result 

 of chemical action of a synthetic nature. 



On both these points it is necessary at present to withhold a 

 definite opinion. 



With regard to the first point, the paranucleins are a group 

 of bodies which are indefinitely characterized and separated to 

 a large extent upon the evidence of the phosphorus content. 

 The percentage of phosphorus in the bodies produced in these 

 experiments was by no means always constant or identical with 

 that usually associated with " paranuclein A." At the same 

 time it was well within the limits usually associated with this 

 class of bodies and it would be natural that the results of syn- 

 thesis, like the starting point of hydrolysis, should be an 

 admixture of bodies. 



In view of the difficulty of characterising " paranuclein," 

 considerable importance attaches to the comparison by Gay and 

 Robertson 1 of the immunity reactions produced by paranuclein, 

 and by this body synthetically produced from the products of 

 hydrolysis. 



These two bodies apparently possess, as tested by sub- 

 cutaneous injections into guinea pigs, identical and specific 

 antigenic properties which are not present in the original 

 products of peptic digestion. It has, however, to be remem- 

 bered that the products of peptic hydrolysis would contain 

 this " synthetic paranuclein," if present, in considerable dilution, 

 and the effects produced by injections might therefore be much 

 less marked. 



1 Gay and Robertson, Journ. of Biol. Client, xii. p. 233. 



