210 1. MALONATE 



cinate, however, actually increases the inhibition. It is likely in this tissue 

 that ion accumulation is obligatorily coupled to the operation of the cycle. 



Effect of Malonate on Mitochondrial Swelling 



Eat liver mitochondria swell quite readily, as measured by changes in 

 light scattering or optical density, when treated with various substances, 

 and the effects of malonate on this phenomenon are interesting. Raaflaub 

 (1953) established that succinate and phosphate promote swelling. This 

 swelling is counteracted by ATP in both cases, but malonate prevents the 

 swelling from succinate only. This was confirmed by Tapley (1956), who 

 extended the list of substances causing swelling to fumarate, malate, gluta- 

 mate, acetate, and a-ketoglutarate. Swelling is prevented by citrate, pyru- 

 vate, and oxalacetate, as well as malonate. Since malonate can prevent the 

 swelling from substrates other than succinate, there is some question as to 

 the specificity of the effect. It was claimed that the same results are obtain- 

 ed in the absence of oxygen and thus that the swelling is not related to the 

 utilization of these substrates. Quite different conclusions were reached by 

 Chappell and GreviUe (1958) inasmuch as they found a good correlation 

 between swelling and utilizable substrates. Malonate prevents the swelling 

 from succinate but not from a-hydroxybutyrate, and, in general, inhibitors 

 blocking oxidations reduced swelling. Matters were further complicated by 

 the results of Keller and Lotspeich (1959 b). They found that phlorizin 

 caused swelling of kidney mitochondria and that this could be counteracted 

 by Mg++, ATP, 2,4-dinitrophenol, and malonate. Hunter et al., (1959 a, b) 

 considered the possibility that swelling is related to the fraction of NAD in 

 the oxidized form, since amobarbital prevents oxidation of NADH and 

 prevents swelling. However, succinate in the presence of amobarbital causes 

 swelling and this is blocked by malonate. Glutamate-induced swelling is not 

 prevented by malonate. It was concluded that swelling depends on electron 

 flow between the substrate and oxygen, and whether or not an inhibitor will 

 prevent swelling is determined by where in the electron transport chain 

 the substrate and the inhibitor act. This does not very well explain the 

 prevention of swelling by 2,4-dinitrophenol and it was suggested that there 

 are at least two different types of mitochondrial swelling. Further confusion 

 was introduced by Sabato and Fonnesu (1959), who found that swelling is 



