72 PHYSIOLOGY OF YEASTS 



The investigations of Mayer, Haydruck and Kusserow, Schulz, 

 Thomas 1 and Lindner, have shown that, among the amides, allan- 

 toin, asparagin, and urea are assimilable by yeasts. It has been 

 pointed out, however, that the investigations of Shiga, Straughn and 

 Jones have indicated in yeast juice the presence of a guanase which 

 transforms guanine into xanthine, and of an arginase which will split 

 xanthine and ornithine into urea. According to Mayer, caffein, 

 creatin, and creatinin are not acted upon by yeasts. 



The investigations of P. Lindner, 2 and his collaborators Rlilke and 

 Hoffmann, have shown that yeasts may assimilate products of their 

 autodigestion. Among those, tyrosine, leucine, adenine, asparagine, 

 aspartic acid and ammonium sulfate are most easily assimilated; 

 finally, choline is used. All of the yeasts, however, do not act in the 

 same manner in this relation. It is thus that the top and bottom yeast 

 of the brewery and distillery types and yeast juice easily assimilate 

 tyrosine, leucine, adenine, aspartic acid, guanidine, arginine, hypo- 

 xanthine, histidine, uracil, choline, thymine, potassium nitrate and 

 ammonium sulfate. Mycoderma and the species of the genus Willia 

 and Pichia use almost all of the products of autolysis. 



More recently, Ehrlich 3 has stated that leucine and isoleucine 

 are especially desirable compounds for yeasts which add a molecule 

 of water, splitting them into isoamyl alcohol (or amyl) and ammonia. 

 The ammonia is used by the yeast. Effront 4 has also given evidence 

 of the existence of an amidase which acts on amino acids but without 

 giving alcohols, transforming them into ammonia and volatile acids. 

 Pringsheim 5 admits the existence of a desamidase which allows yeasts 

 to take their nitrogen from amino acids but without the production 

 of ammonia. The investigations up to the present, then, seem to in- 

 dicate that the amino acids make up a better source of nitrogen for 

 yeasts. Data from Rettger's laboratory allow similar conclusions for 

 the bacteria. Koser and Rettger 6 have shown that the amino acids 



1 Thomas, P. Sur la nutrition azotee de la levure. Comp. Rend. Acad. Sci. 

 131, 1910. 



2 Lindner, P. Riilke, P., and Hoffmann. Wochenschr. Brauerei, 22, No. 40. 

 Lindner, P., and Stockhausen. Wochenschr. Brauerei 3, No. 40 and Bioch. Centr. 

 IV. 



3 Ehrlich, F. Uber die Spaltung racemischer Aminosauren mittels Hefe. 

 Biochemische Zeitschr. 8, 1908. 



4 Effront, I. Action de la levure de biere sur les acides amides. Comp. 

 Rend. Acad. Sciences, 146, 1908. 



5 Pringsheim, H. Ueber die Stickstoffernahrung der Hefe. Biochemische 

 Zeitschrift, 3, 1907. 



6 Koser, S. A. and Rettger, L. F. Studies on Bacterial Metabolism. The 

 Utilization of Nitrogenous Compounds of Definite Chemical Composition. Jour. 

 Inf. Dis. 24 (1919) 301-321. 



