70 PHYSIOLOGY OF YEASTS 



they are able to utilize also as sources of nitrogen, certain enzymes 

 such as pepsin (Mayer and Heinzelmann) . 



According to more recent investigations, the derivatives of al- 

 buminoids (amides, amino acids, and leucomaines) are assimilated 

 more easily than the albumoses and make up the desirable nitrog- 

 enous substances for the yeasts. The work of Rettger has shown the 

 same thing for the bacteria. 



Waterman l stated that the amino group is an especially suitable 

 source of nitrogen. This depends on the presence of one or more 

 acid amide groups which are not available for nutrition. Waterman 

 points out that this selective action of yeasts may be used to separate 

 closely related compounds. Asparagin and aspartic acid are utilized 

 while succinamic and succinamide, which contain only the acid amide 

 groups, are not assimilated. Cinnamamide is not assimilated while 

 a-aminocinnamamide is used. 



Neubauer and Fromherz 2 fermented dl phenylaminoacetic acid 

 (C 6 H 4 OH(NH 2 )COOH) in the presence of 10 per cent of cane sugar 

 for three days. There was left an amount of undecomposed acid 

 which was usually more or less 1. By means of certain methods phenyl- 

 glyoxylic acid hydrazone was obtained. Sodium succinate, benzyl 

 chloride, p-hydroxyphenyl ethyl alcohol (perhaps from yeast tyro- 

 sine), Z-acetylphenylamino acetic acid were obtained. Para-hydroxy- 

 phenylpyruvic acid was also fermented. These authors are led to 

 construct the path from amino acid to the next lower alcohol as fol- 

 lows: 



RCH(NH 2 )COOH = RC(OH)(NH 2 )COOH 



= RCOCOOH = RCHO=RCH 2 OH. 



The processes thus involved are oxidation, decarboxylation, acid 

 reduction. The alcohol acid RCHOHCOOH and the acetylamino 

 acid result from secondary reactions. 



Kossowicz 3 found that yeasts could utilize nitrates. Bokorny 4 

 found that nitrates were unaltered and not assimilated. The simple 

 amines, such as ethyl amine, were also unfavorable. The presence 

 of sugars was found to be necessary to keep down the bacteria. With 

 various sources of nitrogen in the medium, the following increases 

 were observed in dried yeast: 



1 Waterman, H. J. Nitrogen nutrition of compressed yeast. Zent. Biochem.. 

 Biophys. 16, 276. 



2 Neubauer, O., and Fromherc, K. The decomposition of amino acids in 

 yeast fermentation. Zeit. physiol. Chem. 70, 326-350. 



3 Kossowicz, A. Behavior of yeasts and molds towards nitrates. Biochem. 

 Z. 67, 400-19, 1914. 



4 Bokorny, Th. Sources of nitrogen of yeasts. Chem. Ztg. 40 (1916), 

 366-368. 



