INHIBITORS STRUCTURALLY RELATED TO MALONATE 237 



that the greater inhibition of acetate oxidation is evidence for the hydro- 

 lysis of the ester and that the inhibition is exerted by malonate. Malonic 

 diethyl ester was also used to facilitate penetration into Penicillium chryso- 

 genum, since even 100 roM malonate does not effect acetate metabolism 

 (Goldschmidt et al., 1956). The ester at 20 milf inibits the production of 

 C^*02 from labeled acetate 75-85% and simultaneously decreases the in- 

 corporation of C^* into cellular materials, the labeling of glutamate being 

 particularly depressed. The utilization of acetate by Bacillus cereus is also 

 interfered with by malonic diethyl ester, so that acetate and p>Tuvate ac- 

 cumulate (Nakata and Halvorson, 1960). Malonate and the diethyl ester 

 have been compared with respect to their effects on the respiration of 

 Mycobacterium pJdei (Miiller et al., 1960). Malonate stimulates the endoge- 

 nous respiration, presumably through its oxidation, and the ester stimulates 

 even more potently at 1-10 raM, although at 100 mM the ester inhibits 

 and malonate still stimulates. The respiration with glycerol as the substrate 

 behaves similarly. Finally, malonic diethyl ester markedly stimulates the 

 endogenous respiration of Chlorella vulgaris at 4-10 mM, but inhibits the 

 oxidation of glucose and acetate, the latter more strongly (Merrett and 

 Syrett, 1960). All of these results show that the diethyl ester is inhibitory 

 but certainly do not constitute conclusive evidence for a hydrolysis to mal- 

 onate. This is a subject that should be pursued further and more extensive 

 tests should be made for enzymes hydrolyzing the esters. Until the intra- 

 cellular hydrolysis can be established, the results obtained with the malonic 

 esters cannot be interpreted. 



Hydroxy malonate (Tartronate) 



The substitution of a methylene hydrogen of malonate by any group 

 seems to reduce rather strongly the ability to inhibit succinate dehydrogen- 

 ase. Even the small hydroxyl group almost abolishes the inhibitory activity 

 and this is evidence that the binding of malonate to the active center of 

 succinate dehydrogenase must involve severe steric restrictions. Although 

 tartronate does not inhibit succinate dehydrogenase, it has other actions 

 of some interest. Quastel and Wooldridge (1928) found that 71.4 roM tar- 

 tronate does not inhibit succinate oxidation at all whereas it inhibits the 

 oxidation of lactate 90%, as measured by methylene blue reduction in tol- 

 uene-treated E. coli. In fact, the marked differences in the effects of mal- 

 onate and tartronate led Quastel and Wooldridge to postulate the specific 

 structure of the active centers of enzymes. Tartronate inhibits the respira- 

 tion of rat liver slices and is strongly ketogenic, acetoacetate being formed 

 to a greater extent that with equivalent concentrations of malonate (Ed- 

 son, 1936). Pig heart malate dehydrogenase is inhibited 24% by 60 mM 

 tartronate (Green, 1936) but in pigeon liver extracts it is about 1000 times 

 as effective, inhibiting malate oxidation competitively with a ^^ of 0.09 mM 



