492 SCIENCE PROGRESS 



upon concentration. Bayliss * found that as the hydrolysis of 

 caseinogen by tryptase proceeded, the conductivity of the 

 solution increased, but that after concentration of the solution, 

 in the presence of the enzyme, the conductivity diminished. 

 This certainly seems to point to a reversal of reaction in the 

 direction of synthesis. 



More recently Brailsford Robertson 2 has made a very full 

 study of one reaction of this type. His investigations deserve 

 fuller description because of the attempt he has made to meet 

 the theoretical difficulties created by the concentration condi- 

 tions which are found necessary to bring about these reactions. 



In Robertson's initial experiments 400 c.c of N/50 potassium 

 hydroxide saturated with casein were, after complete digestion, 

 concentrated to 70 c.c. To this solution were added 30 c.c. of a 

 10 per cent, solution of Grubler's pepsin. Within two hours a 

 precipitate had formed which was shown to be one of the con- 

 stituents — paranuclein A — of the mixture of proteins which had 

 been previously hydrolysed. 



At first sight this was again to be interpreted as simply a 

 case of a reversible reaction undergoing catalysis, under the 

 concentration conditions existing, in the direction of synthesis ; 

 but further experiments rendered this simpler explanation 

 impossible. In the first place, if this were purely a catalytic 

 action, then the enzyme catalyst could produce no change in the 

 point of equilibrium of the reaction. But as a matter of fact 

 Robertson found that by adding the pepsin in sufficiently con- 

 centrated form, synthesis could be brought about in a solution 

 containing the products of hydrolysis without any previous 

 concentration whatever of this solution. 



Further, it was found possible to obtain the reversible syn- 

 thesis in lower concentration of enzyme and substrate by simply 

 raising the temperature, and in the end ready reversal of the 

 hydrolytic action was obtained at a temperature of 65 C, a 

 temperature ten to fifteen degrees higher than that at which the 

 normal hydrolytic activity of pepsin is known to occur. 



Now obviously these facts cannot be explained upon the 

 usual assumption that the enzyme present is behaving as a 

 normal organic catalyst, in fact the last experiments referred to 

 clearly point to a synthetic action, if catalytic, as resulting from 



1 Bayliss. Nature of Enzyme Action, 2nd ed. p. 53. 



2 T. B. Robertson, Journ. Biol. Chcm. iii. p. 95 and v. p. 493. 



