Adrian Brown. 



Vll 



•character. Here again, however, a field is opened up for further, inquiry — 

 if action take place within the cell, how comes it that such a product is 

 secreted without the organism if this he not destroyed in the process ? 



The activities of B. xylinum were studied, a few years later, by the French 

 chemist, Bertrand, who established the fact that it has an entirely remarkable 

 discriminative power, as in compounds sensitive to its oxidising influence two 

 H.C.OH groups are present, not only in conjunction but so placed that the two 

 OH groups in these are on the same side of the plane in the formula ; thus 

 when the two isomerides formed by reducing sorboses are submitted to the 

 action of the organism 



CH 2 OH— C— 0— C— C— CH 2 OH CH 2 OH— C— C— C— C— <JH 2 OH 



sorbitol alone is oxidised and reconverted into ketose (sorbose). It is in no way 

 clear,at present, whether the selective activity displayed by the organism be that 

 of an enzyme or traceable merely to a peculiarity in the oxidative process. 



The root ideas underlying our present conception of the nature of enzymic 

 hydrolysis are largely traceable to Adrian Brown's iconoclastic work. 

 Beginning with observations on the rate of reproduction of yeast cells, he 

 noticed that a constant amount of yeast fermented an approximately 

 constant weight of sugar, in unit time, in solutions of varying concentration ; 

 the graph of his experiments was a straight line, not a logarithmic curve — 

 indicating the change of regularly diminishing amounts in successive unit 

 periods — such as was held to be expressive of the simple enzymic change 

 conditioned by invertase, on the basis of the experiments made by Cornelius 

 O'Sullivan and Tompson, published in 1890. Hence he was led to re-examine 

 the evidence adduced by these chemists, in support of their view, that the 

 enzymic change was a mass-action effect, strictly comparable with the changes 

 taking place in solutions of crystalloids — in other words, that enzymic change 

 took place in solution. 



He dealt with this subject in an exhaustive manner. The conclusion 

 arrived at was, that during the earlier period of change, as in fermentation, 

 the sugar is hydrolysed at a linear rate, the amount converted being 

 practically independent of the concentration of the solution, in no way pro- 

 portional to it. The rate of hydrolysis is much reduced by the addition of 

 invert sugar, that is to say, of the products of change ; lactose, except in very 

 large proportion, however, has little effect. 



These conclusions have been fully confirmed by later inquiries. It may 

 now be taken as established, that enzymic action is effected at solid surfaces. 

 Complete confirmation of this explanation has been given by recent observa- 

 tions on the action of a catalyst such as finely-divided metallic nickel in 

 determining the hydrogenation of the fatty oils. 



H H OH H 



OH H OH H 



OH OH HOH 



Sorbitol. 



H OHH OH 

 Iditol. 



