1911.] 



The Properties of Colloidal Systems. 



87 



It might be argued against the formation of chemical union of trypsin 

 with caseinogen that when a suspension of free caseinogen (i.e. the free acid, 

 not a salt) is allowed to interact with a solution of trypsin, enzyme is 

 removed by the suspended particles, and if this complex is washed and 

 distributed in water, no hydrolysis of the caseinogen takes place, until alkali is 

 added. It is very possible, however, that the intermediate compound may 

 be formed, but that it is stable in the absence of alkali. 



On the other hand, Starkenstein* has described an experiment which 

 appears to show that the adsorption and chemical compounds are bodies of 

 a distinct nature, if indeed the latter can be said to be formed at all 

 under the conditions in question. Amylase, obtained from the liver, was 

 found to be quite inactive unless an electrolyte such as sodium chloride 

 was present. Accordingly, if a dialysed preparation of the enzyme be 

 shaken up at 40° C. with a mixture of soluble starch and ordinary starch, 

 no formation of sugar occurs. If the mixture be filtered the soluble starch 

 passes through the paper, leaving the rice starch behind. Now, it would 

 be expected that, if a chemical compound were formed, the filtrate would 

 contain it, since the enzyme would more readily combine with soluble starch 

 than with the insoluble body, or at all events with as great readiness. On 

 the contrary, the whole of the enzyme is found in the insoluble starch phase, 

 as shown by the fact that addition of sodium chloride to both fractions and 

 subsequent incubation caused the appearance of abundance of sugar in the 

 latter but none in the filtrate. 



Dietzf also has shown that the synthesis of amyl alcohol and butyric acid 

 to the ester, as catalysed by lipase, takes place entirely in or upon the solid 

 enzyme phase, which is insoluble in the fluid phase. If the solid be filtered 

 off from the reacting system the filtrate undergoes no further change, although 

 when supplied with more enzyme synthesis proceeds. The former enzyme 

 had not lost its activity, moreover, since on adding it to more substrate, 

 reaction went on. 



It occurred to me that some light might be thrown on the question as to 

 whether trypsin is removed from its solution by caseinogen in the form of a 

 chemical or as an adsorption compound, by the investigation of the effect of 

 electrolytes on the process. I have shown! that the absorption by filter- 

 paper of Congo red and other electro-negative colloids is increased by the 

 presence of neutral salts ; the reason is that, both the paper and the colloid 

 having negative charges, there is difficulty in their approximation until the 



* 'Biochem. Zeitschr.,' 1910, vol. 24, p. 218. 



t ' Zeitschr. f. physiol. Chem.,' 1907, vol. 52, p. 314. 



I ' Biochem. Journ.,' 1906, vol. 1, pp. 195—209. 



