114 SCIENCE PROGRESS 



these dual reactions depends upon the extent to which either 

 A 4- B or C + D are present in excess of equilibrium concentra- 

 tion. If A + B are present in excess of equilibrum concentration, 

 then the reaction will be proceeding more rapidly in the direction 

 from left to right, and this will continue to be the case until so 

 much C + D has been formed that the reverse conversion 

 C + D-»A + Bis going on as rapidly as the conversion A + B 

 into C + D. This is the equilibrium point of the reaction and, 

 for a definite reaction, at a definite temperature, is a quite 

 definite point that can be expressed in terms of the concentration 

 of the reacting bodies. 



Now if an enzyme behaves as an ordinary catalyst its 

 addition should make no difference to the position of this 

 equilibrum, but only shorten the time in which this equilibrium 

 point is attained. In such a reaction as 



CuHaOu + H„0 t 2C,H 12 O s 



(maltose) (glucose) 



if the reaction proceeds from right to left it will be of a synthetic 

 nature. Realising this, Croft Hill attempted to obtain con- 

 centration conditions such that the reaction should tend to go 

 from right to left to attain equilibrium, and in this way managed 

 with the use of an enzyme catalyst to synthesise maltose. So 

 far, then, experiment seems to be in agreement with theory, but 

 a closer acquaintance with the literature suggests a number of 

 fresh problems of great importance to the biologist. 



These it is proposed to consider briefly and by no means 

 exhaustively in so far as they touch the two main types of 

 synthesis with which the biologist is particularly concerned, 

 viz. carbohydrate synthesis and protein synthesis. 



Synthesis of Carbohydrates 



It is possible that in the many problems that this subject 

 presents, the study of reversible chemical action as catalysed by 

 enzymes offers us the best experimental method of attack under 

 " in vitro " conditions because it may thus be possible to realise 

 the essential conditions in regard to stereo-isomerism. Emil 

 Fischer, 1 in his Faraday lecture to the Chemical Society, referring 



1 "Synthetical Chemistry in its Relation to Biology," Transactions of Chemical 

 Society ■, 1907, vol. 91. 



