518 ENZYMES DECOMPOSING SACCHABIDES. 



precipitated the invertase beforehand by saturating its solution 

 with ammonium sulphate. 



The chief property of invertase is its power of hydrolysing 

 saccharose, which it splits up into one molecule each of d-glucose 

 and c-fructose according to the equation 



CiaHaOn + H 2 = C B H M 6 + C 6 H 12 6 . 



Whether the enzyme is also capable of hydrolysing other sugars 

 is doubtful : see 332 on this point. 



As already mentioned on p. 511, vol. ii., yeast cannot ferment 

 saccharose directly, the sugar needing to be first hydrolysed by 

 invertase. It is uncertain whether this decomposition is effected 

 inside or outside of the yeast cell. According to O'SuLUVAN (II.), 

 the healthy yeast cell is incapable of diffusing invertase ; and conse- 

 quently the hydrolysis of the saccharose within the cell must precede 

 fermentation. This opinion is shared by HIEPE (I.), who considers 

 that hydrolysis is intimately connected with cell protoplasm, and 

 that the operation is one in which physiological laws play as 

 important a part as chemical laws ; furthermore, that the admis- 

 sion of the saccharose into the cell, and the outward passage of the 

 products of inversion are physiological processes. According to 

 FERNBACH (VI.), the rate at which yeast cells permit the escape of 

 the enzyme is in inverse ratio to their age. In this connection 

 POTTEVIN and NAPIAS (I.) examined five yeasts in a peptonised 

 solution of saccharose, and found that four of the races ceded 

 invertase to the medium in the early stages of fermentation, 

 whilst the fifth did not. These four yeasts yielded powerful 

 solutions of invertase when macerated with chloroform water ; but 

 the fifth only parted with a little invertase after digestion for a 

 fortnight. Hence the individual races of yeast appear to differ in 

 respect of the cession of the enzyme to the circumambient medium. 

 In general, however, it may be assumed that fresh yeast cells 

 belonging to the groups Sacch. cerevisice and Sacch. ellipsoideus I. 

 will allow invertase to diffuse through their cell membrane. 

 BAU (XXIV.) and DONATE (IV.) nevertheless found invertase 

 in all fermented beverages. 



On the constant occurrence of this enzyme in beer, BAU (XXV.) 

 established a method of detecting whether beer has been pas- 

 teurised. One 20 c.c. sample of beer is boiled, and a similar quantity 

 is left unboiled, each being treated with 20 c.c. of a 20 per cent, solu- 

 tion of saccharose, then kept for twenty-four hours at room tem- 

 perature, treated with 0.5 c.c. of lead acetate, made up to 50 c.c. 

 with distilled water, filtered and polarised. Should an appreciable 

 difference be observed in the deviation of the angle of polarisation 

 in the polarimeter, the beer has not been pasteurised ; but if the 

 two results be identical, or approximately so (slight differences in 

 the reading being due to experimental error), the beer will 

 certainly have been pasteurised, and probably at a temperature 



