VITAMINS 201 



mella ulmi grew at a more rapid rate with pyridoxamine than vvith pvri- 

 doxal or pyridoxine (Snell and Rannefelt, 1945). All three forms of this 

 vitamin occur in natural products. Assays for this vitamin are discussed 

 in Chap. 10. 



Mode of action. One of the earliest clues to the action of pyridoxine 

 was discovered by Snell and Guirard (1943) in the interrelationship 

 among glycine, alanine, and pyridoxine and growth of Streptococcus 

 faecalis R. They found that alanine could replace pyridoxine for this 

 organism and that glycine caused inhibition which was overcome by 

 the addition of either alanine or pyridoxine. It was also found that 

 /3-alanine, serine, and threonine inhibited growth. It is possible that 

 alanine serves as a precursor for pyridoxine in this organism, or that one 

 function of pyridoxine is the synthesis of alanine. At any rate the action 

 of pyridoxine appears to be connected with either amino-acid synthesis 

 or amino-acid utilization, or both. Like other vitamins, pyridoxine (or 

 its conversion products) has been assumed to function in the cell as a 

 part of a coenzyme. 



Pyridoxal is phosphorylated before it functions in enzyme systems. 

 In this it is like thiamine and pantothenic acid. Pyridoxal phosphate 

 is said to function as a coenzyme in the transformation of tryptophane 

 into indole by Escherichia coli (Wood et at., 1947). We may assume that 

 the function of this vitamin is the same in the fungi as in the bacteria. 



p-AMINOBENZOIC ACID 

 p-Aminobenzoic acid has the following structure: 



COOH 



NH2 

 p-Aminobenzoic acid 



Rubo and Gillespie (1940) found p-aminobenzoic acid to be a growth 

 factor for nine strains of Clostridium acetohutylicum. Most of the interest 

 in this compound centers in its antagonistic action to sulfonamides. A 

 discussion of this subject is presented in Chapter 11. 



Fungi deficient for p-aminobenzoic acid. Robbins and Ma (1944) 

 reported Rhodotorula aurantica to be deficient for p-aminobenzoic acid 

 and thiamine. Concentrations of as low as 0.03 /xg per liter had a positive 

 effect on the growth of this yeast, while maximum growth was attained 

 in the presence of 3 /zg per liter. The intensity of the pink color developed 

 by this yeast was a function of the p-aminobenzoic acid content of the 

 medium. 



