60 PHYSIOLOGY OF YEASTS 



which liquefy gelatin and those which attack casein. 1 Those which de- 

 stroy the most casein liquefy gelatin most rapidly. Also it seems very 

 probable that the liquefaction of gelatin and the peptonization of casein 

 are due to the action of endotryptase. 



According to Bokorny and Vines, yeasts contain another protease 

 which acts like pepsin; but the existence of this enzyme is rather 

 obscure. 



Buchner and his collaborators have isolated from yeast juice an 

 enzyme which protects albuminous matter from the action of endo- 

 tryptase which they have named antiprotease. This enzyme seems to 

 play an important role in the life of the yeast; it governs the digestive 

 functions and balances the action of the proteases. 



Rennin : The investigations of Boullinger 2 have indicated the pres- 

 ence of rennin in yeasts. This author has verified the existence of ren- 

 nin in certain yeasts by inoculating skimmed milk and after a few 

 months a coagulum formed which gave evidence of the presence of 

 rennin. The curd eventually dissociated under the influence of casease. 



Bochicchio has stated that the Lactomyces infians caseigrana pre- 

 cipitated milk. The same observation has been reported by Dom- 

 browski for other milk yeasts. Other yeasts in milk do not cause this 

 change (yeasts of Adametz, Duclaux and Kayser) . On the other hand, 

 many other species of yeasts (S. glutinia of Sartory) coagulate casein 

 without digesting it, thus secreting rennin but not casease. (Valagussa 

 and Mafera.) 



Nucleases or Enzymes of Nucleo-proteins 



It seems also that yeasts contain enzymes capable of decomposing 

 nucleo-proteins and nucleic bases. Schutzemberger has shown that 

 xanthine, hypoxanthine and guanine are found among the autolytic 

 products of yeasts. Recently Shiga, 3 in making yeast juice act on a 

 solution of guanine, has detected a decrease in the quantity of this base 

 and an increase in the xanthine which would tend to prove the presence 

 of a guanase. According to the same author, yeast juice may also con- 

 tain arginase. When submitting a solution of arginine to the action of 

 yeast juice in the presence of toluene, Shiga has observed a disap- 



1 Diehl (Jour. Inf. Dis. 24 (1919), 347-361) has reported a type of specificity 

 among the bacterial proteases. This author was able to detect a specificity for 

 proteins with certain amino acids, after the bacterium had been grown on media 

 containing these amino acids as the only source of organic nitrogen. 



2 Boullinger, E. Action de la levure de biere sur le lait. Ann. Inst. Pasteur, 

 2, 1897. 



3 Shiga, K. Ueber einige emsige Hafefermente, Zeit. physiol. Chemie, 42. 

 1904. 



