INHIBITION OF SUCCINATE DEHYDROGENASE 15 



oxidative titrations with hot acid permanganate or eerie sulfate (Willard 

 and Young, 1930; Christensen and Ross, 1941) and such methods have 

 been used for the analysis of malonate in the presence of proteins (Ross and 

 Green, 1941). Colorimetric tests, for example with tetrahydroquinoline-iV^- 

 propenal to form blue- violet compounds (sensitive to 0.01 mg malonic acid) 

 (Dieterle and Wenzel, 1944), have been used, and several microcolorimetric 

 and spot tests are available (Feigl, 1960). However, the most valuable 

 methods are chromatographic. A large variety of solvents and spraying 

 agents have been utihzed, and different techniques have been applied: 

 ion-exchange resin columns and partition chromatography (Stark et al., 1951; 

 Phares et al, 1952; Owens et al, 1953; Shkol'nik, 1954; Reinbothe, 1957), 

 strip paper chromatography, both one- and two-dimensional (Buch et al., 

 1952; Cheftel et al, 1952; Denison and Phares, 1952; Duperon, 1956; van 

 Duuren, 1953; Jermstad and Jensen, 1950; Kalyankar et al, 1952; Ladd 

 and Nossal, 1954; Overell. 1952; Smith and Spriestersbach, 1954), and cir- 

 cular paper chromatography (Airan and Barnabas, 1953; Airan et al, 1953; 

 Barnabas, 1955). The use of chromatographic methods for the determina- 

 tion of succinate and malonate in animal tissues is well illustrated in the 

 work of Busch and Potter (1952 a, b; Busch et al., 1952). A moderately sen- 

 sitive method for estimating 10-100 //g of malonate by applying iodine 

 vapor to paper chromatograms was developed by Dittrich (1963). 



INHIBITION OF SUCCINATE DEHYDROGENASE 



The oxidation of succinate in cells is catalyzed by a mitochondrial 

 multienzyme system which is structurally organized into units that can be 

 isolated as a particulate suspension capable of transferring electrons from 

 succinate to oxygen: this complex is known as succinate oxidase. Evidence 

 will be presented that the inhibition of this system by malonate is related 

 to the binding of the malonate to the most proximal site in the sequence, 

 namely, the active center for the attachment and dehydrogenation of succi- 

 nate: this component is known as succinate dehydrogenase. It is impossible 

 at the present time to define the succinate dehydrogenase accurately, be- 

 cause it is assayed with various electron-accepting dyes and the basic mini- 

 mal unit has not been completely characterized. The inhibition of succinate 

 dehydrogenase by malonate has generally been determined with various 

 preparations of succinate oxidase and not with the isolated dehydrogenase, 

 and thus it is necessary to discuss briefly the nature of the entire system. 



Properties of Succinate Oxidase 



Knowledge of the components of succinate oxidase and the pathways of 

 electron flow has been advanced markedly in the past few years (Mahler, 



