32 P-AMINOBENZOIC ACID 



VIII. Effects of Deficiency 



LEMUEL D. WRIGHT and PETER A. TAVORMINA 



A. IN BACTERIA 

 1. Nutrition 



Investigations in bacterial nutrition have uncovered a number of micro- 

 organisms with growth factor requirements for PABA. These species to- 

 gether with their approximate requirements for PABA are summarized in 

 Table VI. Note in particular the wide range in PABA reciuirement from 

 about 0.00003 y per millihter for one-half maximum growth of Lactobacil- 

 lus arabinosus to about 0.001 7 per milliliter for one-half maximum growth 

 of Acetobacter suboxydans. 



The requirement of certain microorganisms for PABA forms the basis 

 for several microbiological methods for the determination of PABA. This 

 subject is discussed in considerable detail under that heading. 



Wyss et al} have shown that the growth factor requirement of a PABA- 

 less mutant of Neurospora crassa-' ^ is a function of the pH of the medium. 

 With increase in the pH of the medium from 4 to 7, larger amounts of 

 PABA are required for equivalent growth in a given length of time. Wyss 

 et al. point out that PABA has a dissociation constant of about 2 X 10~^ 

 At pH 4.8 PABA exists in solution as equal amounts of molecules and ions. 

 At pH 5.8 the molecular form decreases from 50 to 10 %. The portion present 

 as the molecule drops almost tenfold with each unit rise in pH above 5.8. 

 They conclude on the basis of the above data that the efficiency of the 

 vitamin in the nutrition of N^eurospora crassa is a function of the molecular 

 form rather than of the ion. Although the reviewers cannot subscribe to 

 this explanation as the only possible one, the estabhshment of the pH opti- 

 mum for the response of the organism to PABA is of significance in the use 

 of the PABx\-less mutant for the microbiological determination of the fac- 

 tor. 



The specificity of the growth factor requirement for PABA has been ex- 

 amined with a number of species. These data are summarized in Table IV. 

 As might be expected, the ortho and meta isomers of PABA are essentially 

 inactive for all species studied. Rubbo and Gillespie^ have reported that 

 p-aminophenylacetic acid is ten times as active as PABA as a growth factor 

 for Clostridium acetobutylicum. 



It is reasonable to assume from the stmcture of folic acid as well as other 



1 0. Wyss, V. G. Lilly, and L. H. Leonian, Science 99, 18 (1944). 



2 E. L. Tatum and G. W. Beadle, Proc. Natl. Acad. Sci. U.S. 28, 234 (1942). 



s G. W. Beadle and E. L. Tatum, Proc. Natl. Acad. Sci. U.S. 27, 499 (1941). 

 * S. D. Rui)l)<) and J. M. Gillespie, Lancet I, 36 (1942). 



