PERMEABILITY OF CELLS TO MALONATE 187 



Experimental Evidence Relating to the Penetration of Malonate 



Malonic acid is more than 10 times as lethal on injection into frogs as 

 is sodium malonate (Heymans, 1889). No explanation was offered for this 

 observation but it could have been due to the greater permeability of the 

 cells to the acid or, on the other hand, to a nonspecific acidification of the 

 animals. Malonate administered to rabbits circulates initially in a volume 

 equivalent to the extracellular compartment and the intracellular transfer 

 occurs slowly (Wick et al., 1956). The failure of malonate to alter the me- 

 tabolism of labeled acetate was attributed to both the slow penetration into 

 the tissues and the simultaneous metabolism of the malonate, both factors 

 keeping the intracellular concentration at low levels. The inability of mal- 

 onate to alter gastric acid secretion in frogs, even at lethal doses, was sim- 

 ilarly attributed to these factors (Davenport and Chavre, 1956). Inasmuch 

 as succinate oxidase is present in the secretory cells and the cycle is im- 

 portant in secretion (as shown by the inhibition with fluoroacetate), the 

 lack of action must be due to an insufficient concentration within the cells. 



Turning to isolated tissues and cell suspensions, the augmentation of 

 malonate effects by procedures designed to reduce or abolish the perme- 

 ability barriers has been demonstrated many times (Table 1-26). Rat dia- 

 phragm respiration is inhibited slowly by malonate, but if the diaphragm 

 is cut into small pieces, and hence presumably damaged, the inhibition is 

 immediate (Greville, 1936). The oxygen uptake of pigeon brain brei is 

 inhibited rather poorly by 24 mM malonate, but when the brain is dispersed 

 more completely in the form of a homogenate the inhibition is more marked 

 (Banga et al., 1939). The succinate dehydrogenase of yeast incubated for 

 5 hr in liquid nitrogen is much more susceptible to malonate than in normal 

 cells (Lynen, 1943), and the same holds for E. coli treated with toluene 

 (Ajl and Werkman, 1948). Sensitivity to malonate can be induced by liquid 

 nitrogen treatment in the fungus Zygorrhynchus (Moses, 1955) and by dry- 

 ing Pseudomonas (Gray, 1952). Malonate does not inhibit glutamate oxida- 

 tion in intact cells of Pasteurella, but inhibits well in sonic lysates (Kann 

 and Mills, 1955). All of these phenomena have been interpreted in terms of 

 permeability. This is certainly the most obvious explanation and it is prob- 

 ably generally correct, but it must be admitted that such drastic treat- 

 ments could affect many other things; for example, alter the organized 

 enzyme structure so that the attacked enzyme is more exposed, or reduce 

 the ability of the cells to metabolize malonate. 



Only one investigation of the relative permeabilities of the dicarboxy- 

 late anions has been made. Giebel and Passow (1960) determined the half- 

 times for penetration of these ions into bovine erythrocytes and the results 

 are given in Table 1-27. Giebel and Passow attempted to correlate the per- 

 meabilities with the ionic sizes and the acidic ionization constants. The 

 ionic volumes and lengths presented in the table, which are somewhat 



