328 2. ANALOGS OF ENZYME REACTION COMPONENTS 



= 21 mM, and K^ = 23 milf ) (Wingo and Awapara, 1950), which is rather 

 surprising because of the shorter intercarboxylate distance. 



Ghitamate decarboxylase from the squash Curcurbita moscliata is inhib- 

 ited competitively by a variety of organic acids (see accompanying tabu- 

 lation), and the results are of some interest with regard to structure and 



Inhibitor (13.6 mM) % Inhibition 



Monocarboxylates 



Formate 17 



Acetate 42 



Propionate 10 



7i-Butyrate 18 



Isobutyrate 8 



n-Valerate 25 



Iso valerate 15 



n-Caproate 24 



Isocaproate 20 



Dicarboxylates (saturated) 



Oxalate 



Malonate 



Succinate 



Glutarate 24 



Adipate 49 



Pimelate 58 



Suberate 37 



Dicarboxylates (unsaturated) 



Fumarate 



Maleate 14 



Citraconate 



Mesaconate 7 



Itaconate 11 



Tricarboxylates 



cis-Aconitate 29 



irans-Aconitate 18 



intercarboxylate distance (Ohno and Okunuki, 1962). Glutamate concen- 

 tration was 27.2 mM in all cases. Many amino acids examined are weakly 

 inhibitory or without effect. The maximal inhibition by pimelate in its 

 series probably indicates that a cambering of the molecule is necessary for 

 binding of the two carboxylate groups, or possibly that the cationic groups 

 of the enzyme are farther apart than in glutamate. The relatively high 



