ESSENTIAL NONMETALUC ELEMENTS 



109 



thecium verrucaria, which make hmited growth on ammonium nitrogen do 

 so because they are unable to synthesize in adecjuate amounts the neces- 

 sary three-, four-, and five-carbon keto acids. The interrelation among 

 various dicarboxylic acids is shown in schemes IV, VIII, and IX. 



The reactions discussed above account for the synthesis of only a few of 

 the 20 or so amino acids found in fungus protein. Another type of reac- 

 tion may account for the synthesis of secondary amino acids. This is 

 called the transamination reaction and may be represented as follows : 



R— CO— COOH + R'— CH(NH2)C00H -^ R— CH(NH2)C00H+R'— CO— COOK 



According to Roine (1947), Torulopsis utilis has the necessary enzymatic 

 mechanisms for the synthesis of the following amino acids by transamina- 



se 



30 40 50 



Time in minutes 



60 



70 



Fig. 19. Amounts of soluble nitrogen compounds found in the trichloroacetic acid 

 extract as a function of time. Data are based on 100 ml. of yeast suspension, or 

 about 5 g. fresh yeast. Curve 1 represents total soluble nitrogen, curve 2 total 

 amide nitrogen, curve 3 alanine nitrogen, and curve 4 dicarboxylic-amino-acid nitro- 

 gen. (Courtesy of Roine, Ann. Acad. Sci. Fennicae 26: 63, 1947.) 



tion: aspartic acid, glutamic acid, alanine, valine, leucine, and isoleucine. 

 For a general review of the transamination reaction, see Herbst (1944). 

 Roine (1947) has obtained experimental evidence which indicates that 

 in Torulopsis utilis the primary amino acids are formed first and that the 

 secondary amino acids are then formed from them. This evidence w^as 

 obtained by analyzing the nonprotein nitrogen fraction which was 

 extracted from cells of various ages with trichloroacetic acid (a protein 

 precipitant) . Nitrogen-starved cells of T. utilis were suspended in carbo- 

 hydrate-free medium which contained ammonium nitrogen. The culture 

 was aerated. Every 10 min. a portion of the crop was harvested, and the 

 distribution of nitrogen compounds in the trichloroacetic acid extract was 

 determined. Figure 19 show clearly that the first stages of protein syn- 

 thesis consist in the formation of monoamino dicarboxylic acids, their 



