570 Dr. Armstrong and Prof. Armstrong. Studies on [June 13, 



Having thus called attention to the various factors concerned in the 

 hydrolysis, we may now point out that our hypothesis involves the assumption 

 that the relationship of the acceptor section of the enzyme to hydrolyte is 

 not that of lock and key but that of a superposable and therefore practically 

 identical radicle. As a matter of fact, the lock and key relationship, taken 

 strictly, is unknown and even inconceivable : the only known relationship 

 among similar substances is that of object and image : this is clearly not the 

 relationship which holds between enzymes and their correlated hydrolytes. 



We use the expression practically identical advisedly, in view of the fact 

 that the tetramethylated methyl-/3-glucosides* and certain glucosaminet 

 derivatives are all hydrolysed by " emulsin " (prunase). Apparently therefore 

 the spatial arrangement of the several radicles in the hydrolyte and the 

 correlated acceptor must be the same in so far as the relative distribution of 

 negative and positive is concerned but the negative groups admit of variation 

 within certain limits — i.e. methoxyl may take the place of hydroxyl and 

 apparently even the radicle NH 2 may to some extent be substituted for 

 hydroxyl. 



The enzymes which hydrolyse the glucosides generally may well be com- 

 pounds of the glucoprotein class containing either a- or /3-glucosidic radicles 

 and capable therefore of hydrolysing either «- or /3-glucosides, as the case 

 may be, because their configuration harmonises either with that of the one 

 or with that of the other type of compound. 



To take another example, it appears not improbable that urease is an 

 enzyme in which the urea residue in arginine is in suitable relationship with 

 the carboxyl group. 



Special Efficiency of Enzymes. — With regard to the efficiency of saccharo- 

 clasticj enzymes, two points have to be considered — the efficiency of the 

 car boxy lie radicle which we assume to be the agent and the special efficiency 

 of a colloid mechanism such as we have pictured. It is well known that the 

 efficiency of the carboxylic radicle varies greatly, being very low in the 

 majority of acids but relatively high in formic acid and considerably higher 

 in the substituted acetic acids, especially in trichloracetic acid ; it is therefore 

 conceivable that it may have a relatively high efficiency in the enzymes, 

 especially if the region within which it is immediately active be one of high 

 concentration. 



As to the special efficiency of a colloid mechanism, as we have elsewhere 



* Irvine and Cameron, ' Cheni. Soc. Trans.,' 1905, vol. 87, p. 900. 

 t Irvine and Hynd, ibid., 1913, vol. 103, p. 41. 



% We regret that in earlier communications we have been guilty of using the inde- 

 fensible terms "sucrose" and " sucroclastic " in place of '"saccharose" and " saccharo- 

 ' clastic." 



