2 1. MALONATE 



berg (1909) in Lund. He had observed the inhibition of minced frog muscle 

 respiration by oxalate and decided to study the higher homologs. Thus the 

 inhibitory action of malonate on muscle respiration was demonstrated, 

 whereas succinate instead stimulated the oxygen uptake. Apparently this 

 observation went unnoticed and the inhibitory activity had to be rediscov- 

 ered later. Rose (1924) at Illinois showed that malonate exhibits no nephro- 

 toxic action, as does glutarate, when given orally to rabbits, although he 

 later (Corley and Rose, 1926) found that the methyl and ethyl derivatives 

 depress renal function. At about the same time, Momose (1925) in Japan, 

 continuing the work of Pohl, observed that malonate when perfused through 

 dog liver, gives rise to acetoacetate, acetone, and aldol. He postulated that 

 these substances arise from malonate after decarboxylation to acetate, but 

 it is more likely from our present knowledge that malonate gives rise to 

 these substances by a disturbance of the metabolism. During the next 

 few years evidence was accumulated that malonate can arise from normal 

 tissue metabolism — occurring in alfalfa (Turner and Hartman, 1925) 

 and wheat (Nelson and Hasselbring, 1931), and appearing during citrate 

 fermentation in the mold Aspergillus (Challenger et al., 1927) — and be 

 metabolized by certain microorganisms, such as Escherichia coli (Grey, 

 1924). 



Our present concepts of the inhibitory action of malonate, however, 

 arose from the work on bacterial dehydrogenations by Quastel and Whetham 

 (1925) at Cambridge. They tested the abilities of various dicarboxylic acids 

 to reduce methylene blue in suspensions of E. coli and found that only suc- 

 cinate is active. Malonate inhibited this reduction by succinate. As stated 

 in their own words, "Oxalic, glutaric, and adipic acids (when mixed with 

 succinic acid) do not retard the reduction due to the succinic acid, but 

 malonic acid has a definite retarding effect. It is difficult to explain the 

 anomalous behaviour of malonic acid, but there is no doubt as to the reality 

 of the effect." They found the methylene blue reduction time with succinate 

 bo be tripled in the presence of 77 mM malonate. Quastel and Wooldridge 

 (1928) extended this work to show that the action on succinate oxidation is 

 rather specific in that malonate does not appreciably inhibit the oxidation 

 of several other substrates by E. coli. But in addition they demonstrated 

 that increasing succinate concentrations would counteract the malonate 

 inhibition, leading them to suggest that both substances are adsorbed to 

 the enzyme reversibly, probably competing for the same active site. Final- 

 ly, Quastel and Wheatley (1931), now at the Cardiff City Mental Hospital, 

 reported that the malonate inhibition of succinate oxidation occurs in 

 many bacteria, and in mammalian brain and muscle as well, the enzymes 

 from the mammalian tissue being even more sensitive. 



The concept of the competitive inhibition of an enzyme by a substance 

 structurally related to the normal substrate was first clearly demonstrated 



