The Origin of Life 25 



also act in the opposite direction, namely synthetically. 

 Thus it should not only be possible to digest proteins 

 with pepsin but also to synthetize them from the pro- 

 ducts of digestion with the aid of the same enzyme. 

 This expectation was based on the idea that the enzyme 

 did not alter the equilibrium between the hydrolyzed 

 and non-hydrolyzed part of the substrate but only 

 accelerated the rate with which the equilibrium was 

 reached. Van't Hoff's idea omitted, however, the pos- 

 sibility that in the transitory combination between 

 enzyme molecule and substrate a change in the molec- 

 ular configuration of the substrate or in the distribution 

 of intramolecular strain may take place. The first 

 apparently complete confirmation of van't Hoff's sug- 

 gestion appeared in the form of the synthesis of maltose 

 from grape sugar by the enzyme maltase, which decom- 

 poses maltose into grape sugar. By adding the enzyme 

 maltase from yeast to a forty per cent, solution of 

 glucose Croft Hill' obtained a good yield of mal- 

 tose. It turned out, however, that what he took for 

 maltose was not this compound but an isomer, name- 

 ly isomaltose, which has a different molecular con- 

 figuration and cannot be hydrolyzed by the enzyme 

 maltase. 



Lactose is hydrolyzed from kephyr by an enzyme 

 lactase into galactose and glucose; by adding this 

 enzyme to galactose and glucose a synthesis was 



* Hill, C, Jour. Chem. Soc, 1898, Ixxiii., 634. 



