CATALYSIS AND ENZYMES 323 



either by increasing (alcohol) (acid) or by decreasing (ester). In point of fact, 

 of course, the two are identical, since one cannot take place without the other! 

 The result of excess of water should be, therefore, to increase the hydrolytic 

 reaction of the system, as found by experiment. 



The conclusion to be drawn from this fact is that, in order to obtain much 

 indication of the synthetic aspect of enzyme action, the concentration of water 

 must be diminished as far as possible (Fig. 80, page 300). 



In the living cells, where synthetic processes readily take place, it seems that 

 there must be some very effective means of doing this, perhaps by surface con- 

 densation or imbibition on the part of colloids. But we have as yet no very clear 

 idea of the mechanism. 



As has been pointed out above, certain synthetic reactions proceed but very 

 slowly, even in maximum concentration of the reagents, on account of their 

 chemical nature itself. But, in the dynamic and heterogeneous systems of the 

 cell, this small amount of synthesis must not be undervalued. Suppose that, as 

 soon as equilibrium is established, the synthetic products are removed in some 

 way. More will be formed in order to re-establish the stable condition and, in 

 this manner, the process may be continuous, so that a quite appreciable degree of 

 synthesis may take place in a short time, depending on the extent to which the 

 reaction is accelerated by an enzyme. The removal may be effected in several 

 ways. The product may be washed away by the blood current to some other part 

 of the organism, it may be deposited in the form of a separate phase, such as 

 starch, glycogen, or fat, or it may be immediately used up in an independent 

 chemical reaction. 



A particular enzyme in a cell, for example amylase in the liver, will, under 

 low concentrations of glucose in the blood, hydrolyse the glycogen stored in the 

 cell ; while, in higher concentrations of glucose, glycogen will be synthesised 

 and, as it is stored in an insoluble form, the process can go on to a considerable 

 extent. This possibility has been pointed out by Croft Hill (1898). 



The hydrolysis and loss of starch from germinating seeds is regulated by the 

 growing plant. If the embryo is removed, the starch cea,ses to be hydrolysed. 

 This is obviously a case of equilibrium of the kind just referred to, since Pfeffer 

 and Hansteen (1893) have shown that, if the embryo of maize or barley be 

 replaced by a little column of plaster of Paris, the disappearance of starch can be 

 stopped or set going again according as the end of the plaster column is immersed 

 in a tiny drop of water or in a large quantity. In the former case, the products 

 of hydrolysis are not removed, so that the reaction soon comes to its equilibrium 

 position. In the latter case, they are removed by diffusion as fast as they are formed, 

 so that their concentration is maintained permanently low and no equilibrium 

 is reached. 



The reader is referred to the chapter on the reversibility of enzyme action in 

 my monograph (1913, 2) for the numerous cases in which direct evidence of 

 synthesis by enzymes has been observed. The fact must be again emphasised that 

 there is no necessity for the assumption of special synthesising enzymes and that 

 all evidence that has been brought forward to show their existence has been shown 

 to be capable of other explanations (Bayliss, 1913, 1). If enzymes are catalysts 

 and if the reactions are reversible ones, enzymes must accelerate both the 

 hydrolytic and the synthetic aspects, unless they carry the reaction to completion 

 in one direction, whatever the conditions present. 



It was mentioned incidentally at the beginning of the present chapter that 

 the actual position of equilibrium is frequently found to be somewhat different 

 under the action of enzymes from that under acids. This fact seems to have 

 caused some difficulty. But there are one or two considerations, of interest 

 in themselves, which should, I think, lessen or remove the difficulty. The 

 difficulty itself would be much more serious if these enzyme changes were 

 associated with any considerable heat change, since, in that case, energy would 

 have to be supplied by the enzyme or from some other source. But since the active 

 enzyme is always present in minute amount compared with that of the substrate 

 it does not seem possible that it could supply any appreciable amount of energy, 



