312 2. MALE ATE 



certain instances. It should be clear that slight to moderate stimulation of 

 respiration by maleate does not constitute sufficient evidence for its metab- 

 olism. In studying the metabolism of maleate, one must be particularly 

 careful to use a preparation free from fumarate, and this factor makes 

 some of the early work difficult to interpret because the purity of the mal- 

 eate used is unknown. 



Organisms and tissue preparations may be divided into three categories 

 with respect to the utilization of maleate. 



(A) Maleate not utilized 



Bacteria: Bacillus subtilis, E. coli, Proteus, Pseudomonas, Salmonella, Shigella 

 (NicoUe and Joyeux, 1950), and 14 strains of Pseudomonas (Shilo and 

 Stanier, 1957) 



Fungi: Aspergillus and Penicillium sp. (Berk et ah, 1957) 



Yeast: Saccharomyces (Jung and Miiller, 1922) 



Animal tissues: frog muscle (Dakin, 1922) and beef testis and kidney (Hallman, 

 1938, 1940) 



(B) Maleate definitely metabolized 



Bacteria: Klebsiella pneumoniae (Nicolle and Joyeux, 1950) and Pseudomonas 



strain Maleic 5 (Shilo and Stanier, 1957) 

 Plants: wheat roots (Lundegardh, 1944) and tobacco leaves (Vickery and 



Palmer, 1956 a) 

 Animals: dogs (Sacks, 1958) and rats (Taggart et al., 1962) 



(C) Maleate possibly metabolized {evidence not clear-cut) or slightly metabolized 



Bacteria: Azotobacter (<4% metabolized) (Lineweaver, 1933) and Rhizobium 



strains (Burris and Wilson, 1939) 

 Plants: bean and tomato plants (Greulach, 1953) 

 Animals: rats (Krusius, 1940), rabbits (Krebs et al., 1938), and dogs (Orten and 



Smith, 1937) — evidence in all these from increased citrate excretion 



There are, of course, a number of instances in which maleate has been used 

 and no evidence for its metabolism has been noted, although this was not 

 tested directly. The results are equivocal in some of the early work and the 

 conclusions reached are now subject to doubt. Ohta (1912) reported that 

 dog livers perfused with maleate formed acetoacetate, and believed that 

 maleate was converted to acetoacetate, but possibly this is the result of 

 a disturbance in the metabolism brought about by maleate. Thunberg 

 (1920) found that maleate decolorized methylene blue in the presence of 

 frog muscle mince and discussed the possibility that it was oxidized to 

 acetylenedicarboxylate. Laki (1935) thought that maleate can be reduced 

 like fumarate in extracts from muscle, but this has not been confirmed. 

 Fabisch (1931) reported the esterification of maleate in the presence of 



