ENZYMES AS SYNTHETIC AGENTS 117 



with glucose, but the intermediate stages in what is undoubtedly 

 a complex process are still in dispute, 1 and in any case zymase 

 is not at present regarded as an important factor in the decom- 

 position of sugar in the aerobic tissues of the plant, though it 

 apparently occurs in the higher plants and especially in massive 

 ill-aerated tissues. It is to oxidases that the catalysis of the 

 sugar in the aerobic tissues is generally ascribed, and as the 

 details of this process have never, I think, been followed in vitro, 

 stages in this return from sugar to carbon dioxide and water are 

 still quite obscure. 



This being so, we can only suggest from our present standpoint 

 that if formaldehyde be the first formed product, a ^-glucose 

 would be the first sugar likely to be formed, and we may now 

 proceed to consider whether any light is thrown upon the next 

 step, if it is considered as a condensation of two molecules of 

 dextrose to give maltose, the process being accelerated by the 

 enzyme maltase. 



I fear that in the present state of the literature of the subject 

 our conclusion will be that though the idea may be suggestive, 

 the subject is too full of contradictions to enable one to reach 

 any hypothesis with a satisfactory decisiveness. 



It was previously pointed out that Croft Hill described the 

 synthesis of maltose from glucose by the aid of the enzymes of 

 an extract of yeast which contained considerable quantities of 

 maltase. But a difficulty arose when it was subsequently 

 pointed out, and the statement confirmed later by E. F. Arm- 

 strong, that the di-saccharose formed was an isomer of maltose 

 and termed iso-maltose. This point has since become of consider- 

 able importance as the actions of enzymes have been more fully 

 investigated and their properties become more strictly defined. 



It is realised that the molecule glucose, containing several 

 asymmetric carbon atoms, can exist in a large number of isomeric 

 forms, and that moreover the dextro-isomer, ^-glucose can itself 

 exist in two stereo-isomeric forms which can pass over into 

 one another through an intermediate modification. 2 



1 For a review of recent literature, see Harden, "Alcoholic Fermentation," 

 Monographs on Biochemistry. 



a More probably a stable equilibrium point exists between the two forms when 

 in solution (Lowry). For a clear account of these problems of sugar constitution, 

 see E. F. Armstrong, " The Simpler Carbohydrates and the Glucosides," Mono- 

 graphs on Biochemistry. 



