14 P-AMINOBENZOIC ACID 



jugatioii of PABA and glycine as a model system for the study of peptide 

 bond formation. Uat liver and kidney cortex slices (but not heart, testis, 

 muscle, brain, or spleen) were found to carry out the synthesis of p-amino- 

 hippuric acid (PAHA). The reaction is aerobic and will not proceed in the 

 presence of cyanide, arsenite, iodoacetate, azide, fluoride, or malonate.^ 

 Adenosinetriphosphate, however, will support the synthesis anaerobically. 

 Potassium and magnesium ions stimulate the conjugation, phosphate is 

 without effect, and calcium is inhibitory.'' In order to maintain the reaction 

 at low tissue concentrations the addition of members of the citric acid cycle 

 was found necessary. Under anaerobic conditions the addition of diphospho- 

 pyridine nucleotide (DPN) inhibits the synthesis, presumably by diverting 

 to other reactions the energy furnished by ATP. The enzyme system re- 

 sponsible for PAHA synthesis was found associated with the large insoluble 

 particles of the liver cells and is unstable to freezing, acetone-drying, and 

 non-isotonic concentrations of salt.^ Cohen and McGilvery suggest the 

 name "synthetase" for enzymes involved in the formation of amides and 

 esters exclusive of phosphate esters. 



The findings of Cohen and McGilvery regarding PAHA formation were 

 confirmed by Beyer and his associates.^ The latter workers, employing 

 guinea pig liver and renal cortex, observed that conjugation is essentially 

 complete in 1 hour. Beyer et al.^ report that "benemid" produces 70 % in- 



CHsCH-CH. 



NSO2— 4 ^— COOH 



CH3CH2CH2 



"Benemid" 



hibition of the synthesis at a concentration of 25 X 10~^ M, without, how- 

 ever, affecting the oxygen uptake in the aerobic system. PAHA formation 

 in the ATP-anaerobic system is also inhibited by "benemid." The com- 

 pound has no effect, however, on the in vitro phosphorylation of glucose. 

 The authors interpret the data to mean that "benemid" exerts its inhibi- 

 tory action specifically by obstructing the utilization of energy by the con- 

 jugase, rather than by affecting the production of high energy phosphates. 

 The inhibitory action of a nitrogen mustard (methylbis-jS-chloroethyl- 

 amine hydrochloride) on PAHA formation in rat liver slices is similarly 

 interpreted by McKinney'^ as being directed specifically toward the "syn- 

 thetase" rather than involving the reactions which produce or utilize en- 

 ergy. 



6 K. H. Beyer, V. 1). VViebelhaus, K. K. Tillsou, II. F. lUisso, and K. AI. Willioyte, 



Proc. Soc. Expil. Biol. Med. 74, 772 (1950). 

 ^G. R. McKinney, /. Pharmacol. Exptl. Therap. 96, 188 (1949). 



