16 



Amino Acids and Related Compounds 



A general review of the intermediary metabolism of amino 

 acids would be disproportionate to the scope of this book. It is 

 only possible to sketch in here some relationships and biosyn- 

 thetic sequences which may serve as reminders or as guides for 

 the novice. 



As in acetate metabolism microorganisms have been used to 

 explore the network of metabolic relationships among the amino 

 acids. Many of these have proved quite general, yet it is only 

 necessary to consider the unusual amino acids which have been 

 isolated from microbial sources to realize the differences from 

 human metabolism. 



In this section principally free amino acids are considered. 

 Polypeptides are listed and discussed in the succeeding section. 

 Amino acid isolation and assay formerly were tedious and gen- 

 erally confined to analysis of hydrolysates of total proteins. Pa- 

 per chromatography and reliable microbiological assays have 

 made possible the separation and assay of the low concentra- 

 tions of amino acids evolved into fermentation broths. 



The older work on fungi has been reviewed.^ A semiquanti- 

 tative survey of the free amino acids of a taxonomic range of 

 fungi gave the results shown in Table P on page 300. In 

 general there were found no outstanding differences in the 

 quantities or types of amino acids produced by the different 

 fungi, nor in the types produced by fungi as compared with 

 those of higher plants. The absence of tryptophan in all species 

 examined is noteworthy. Four unidentified compounds were 

 found in various fungi. These were suggested tentatively as 



1 Jackson W. Foster, "Chemical Activities of Fungi," Academic 

 Press, New York, 1949. 



2R. Close, Nature 185 609 (1960). 



