INVERTASE 127 



is, therefore, an enzyme capable of passing through the cell 

 wall, and thus belongs to the class known as extra-cellular 

 enzymes, in contradistinction to other enzymes found in 

 yeast such as maltose and zymase, which are only obtained if 

 the cell wall is partially, at any rate, broken down. 



Invertase can be separated from solution in the ordinary 

 way by precipitation with alcohol, as was first shown by 

 Berthelot. It has been exhaustively investigated by O'Sulli- 

 van and Thompson. The best yield of invertase was obtained 

 from yeast liquor, which results when well pressed sound 

 yeast is allowed to stand for some time. A process of self- 

 digestion then sets in, the yeast being converted into a dark- 

 coloured liquid with a characteristic but not unpleasant 

 smell. An addition of 47 per cent, of alcohol to this liquid 

 gives a good precipitate of invertase. They found that the 

 action of invertase on cane sugar proceeded in accordance 

 with the law which has been found to obtain in purely 

 chemical reactions, in which no condition varies except 

 the diminution of the changing substance ; i.e., if the 

 quantities of sugar inverted were plotted as ordinates to 

 a curve, and the corresponding times as abscissae, a definite 

 time curve resulted. 



The speed of the reaction was found to increase with the 

 temperature up to 55-60 C., but at 75 C. the enzyme is 

 destroyed. 



Caustic alkalis were found to be instantly destructive of 

 the enzyme, whereas minute quantities of sulphuric acid were 

 favourable to its action. Any excess of acid above a defined 

 minimum was, however, detrimental in its effect. 



There appeared to be no limit to the activity of the 

 enzyme, as a sample of invertase which had inverted 100,000 

 times its own weight of sugar was still active. 



It is noteworthy, in view of the more recent work on 

 maltase, that the products of the reaction appeared to have 

 no effect on its rate ; on the other hand, the enzyme can 



