IV. BIOCHEMICAL SYSTEMS 



15 



Recently, Woollcy^ reported that the thiaminase founcl in an extract of 

 carp viscera when incubated with sjnithetic 2-amino-}-hydroxy-()-pteridyl- 

 inethyl-(4'-methyl-5'-hydroxyethylthiazoHum) bromide and PABA will 

 yield ptiMoic acid. Sub.^titiition of />-aininobenzoylglutamic acid for P.\]iA 



on 



N 



-CHr 



>' 



H.X 



/^N/\X^ 



carp 

 thiaminase 



OH 



CH2NH- 



-COOH 



/^n/\n^ 



H2N 



gives rise to folic acid. Woolley points out that the specificity of the enzyme 

 appears to be for the thiazolium group, and that this is not necessarily the 

 mechanism whereby PABA is transformed into folic acid. The experiment 

 is especialh^ worthy of note in that a new biosynthetic mechanism is pre- 

 sented, i.e., one in which the energy for the reaction is derived from a 

 quaternary ammonium ion rather than from a high-energy phosphate bond. 



Baur and Riif^ were able to demonstrate that low concentrations of 

 PABA, or of sulfanilic acid, sulfathiazole, sulfanilamide, and sulfapyri- 

 dine, inhibit to a considerable extent the air oxidation of hydro(iuinone as 

 well as the degradation of tyrosine by potato tyrosinase. 



Another indication that PABA exerts some influence on an enzyme 

 system is to be found in the work of Mayer,''' who obser\ed that the growth 

 of Mycobacterium tuberculosis in a medium containing PABA is attended 

 by the formation of a yellow pigment. The pigment appears to consist, in 

 part at least, of some oxidation product of PABA, produced by a specific 

 oxidase which requires ions of magnesium and iron for acti\ity. As might 

 well be anticipated, glucose, ascorbic acid and cyanide repress the enzy- 

 matic action, and pigment is not produced. 



According to Makino and Yamamoto" rabbit and cattle livers contain 

 an enzym(> which cleaves folic acid. The authors, using the methylene blue 



« D. W. Woolley, J. Am. Chcm. Soc. 73, 1898 (1951). 



' ]•:. Baur and H. lUif, Hclv. Chim. Acta 25, 52.3 (1942). 

 10 R. L. Mayer, J. Bnctcriol. 48, 3.37 (1944). 

 " K. Makino and K. Yamamoto, Science 113, 212 (1951). 



