10. Vitamin Requirements 

 of 

 Fungi 



F 



ungi, like all other organisms so far known, require 

 minute amounts of specific organic compounds for growth. The cell 

 may synthesize its own supply of one of these growth factors, or it may 

 be dependent, in whole or in part, on an exogenous supply. Commonly, 

 we refer to the dependence on exogenous supply as a requirement, 

 realizing that the organism which synthesizes its own growth factors is 

 equally "dependent" on them for normal metabolism. 



The definition of growth factors may be broad or narrow. We may, 

 for example, include as growth substances all compounds required in 

 small amounts and not used for energy (260). This broader definition 

 includes amino acids, purines, and choline as growth factors. A nar- 

 rower concept, the one used here, excludes compounds that function 

 as structural materials, even though they are needed in small amounts. 



Most of the known vitamins have a catalytic function in the cell as 

 coenzymes or constituent parts of coenzymes. This function is stressed 

 in the definition of vitamins employed in this chapter: organic mole- 

 cules required in small amounts and not, so far as we know, used as 

 sources of either energy or structural materials of protoplasm. This 

 definition is arbitrary and provisional. Arbitrary, because it separates 

 constituents of coenzymes (e.g., riboflavin) from constituents of en- 

 zymes (e.g., amino acids) and cannot separate, for example, the role 

 of adenine in adenosine triphosphate from its role in the structure of 

 nucleic acids. Provisional, because the cofactor role of some of the 

 vitamins, especially inositol, is uncertain. 



