550 ENDOTRYPTASE AND PHILOTHION. 



neutralised, heated to boiling, acidified with a few drops of acetic 

 acid, and filtered through a dry filter after having been made up 

 to a definite volume on cooling. The nitrogen in an aliquot part 

 of the filtrate is then determined by the Kjeldahl method. By 

 performing the determination with fresh and digested juice, the 

 increased amount of nitrogen in the filtrate gives a very accu- 

 rate representation of the progress of digestion. According to 

 SALKOWSKI (II.) the determination is effected in precisely the 

 same manner in the case of yeast suspended in water, the nitrogen 

 being determined in the filtrate (separated from the coagulum) 

 before and after the digestion of the yeast in water containing a 

 little chloroform or toluol. The proteid nitrogen may be deter- 

 mined either in the coagulum, or else, according to IWANOFF (II.), 

 in the precipitate furnished by copper oxide (Stutxer). 



Chief among the properties of endotryptase ranks its practically 

 valuable behaviour toward high and low temperatures. Tempera- 

 ture is the decisive factor, not only for the decomposition of proteid s 

 during fermentation (as already mentioned several times in 

 chap. Ixiii.), but also for the activity of alcoholase, which enzyme 

 may, in certain circumstances, be injuriously affected by the endo- 

 tryptase that is acting concurrently. All experiments on the 

 properties of endotryptase may be carried out in a most satisfac- 

 tory manner with expressed meat juice which, to some extent, 

 represents a solution of this enzyme, and forms the best material 

 from which the action of the enzyme can be quantitatively deter- 

 mined. Geret and Hahn obtained the accompanying particulars 

 (see Tables on next page) with regard to the optimum and 

 destruction temperatures of the enzyme. 



The optimum temperature seems therefore to lie between 40 

 and 45 0., whilst the enzyme is completely destroyed by heating 

 at 60 C. for an hour. In the dry state, both in pressed yeast juice 

 and permanent yeast, endotryptase naturally exhibits higher 

 powers of resistance to heat. On the other hand, at low tempera- 

 tures (3 to 7 C.) as was shown by an experiment continued for 

 fourteen days by Hahn and Geret the digestion, though by no 

 means entirely prevented, is so considerably delayed as to demon- 

 strate the advantage of carrying out ordinary yeast fermentations 

 at low temperatures, in view of the protection of the alcoholase 

 (see p. 473, vol. ii.). 



As in the case of other proteolytic enzymes, the influence of 

 gases on the action of endotryptase seems to be very slight. Lack 

 of oxygen was shown by the experiments of GEHET and HAHN 

 (I. and II.) to have no such favourable influence on the proteolysis 

 of pressed yeast juice as was reported by WILL (XXXV.) in the 

 case of the living cells. On the contrary, the passage of air or 

 oxygen was found rather to stimulate the digestion of protein ; 

 whilst the operation proceeded unhindered by the passage of a 

 current of carbon dioxide or hydrogen. So far as carbon dioxide 



