ALIPHATIC ORGANIC ACIDS 145 



352, 384). Distinctive features include the very low pH optimum — 

 about 1.9 for shaken cultures — and the pronounced effects of sodium 

 chloride and magnesium sulfate under certain conditions. The low 

 pH optimum of the processes has been shown conclusively (334) to be 

 determined by the fact that the enzyme system for itaconate formation 

 is present only during cultivation at low pH. 



Itaconic acid is formed in vitro from ds-aconitic acid by the enzyme 

 cis-aconitic decarboxylase (41); since n's-aconitate is a component of the 

 tricarboxylic acid cycle, the formation of itaconic acid may be regarded 

 as an alternate metabolic pathway for glucose carbon (Figure 1). 



A mutant of Aspergillus terreus, obtained by ultraviolet irradiation, 

 forms a mixture of itatartaric acid and its lactone (492). The struc- 

 ture (Table 1) has an obvious resemblance to that of itaconate, and 

 it is reasonable to suppose that the two acids are biochemically related. 



Other Acids. Tartaric acid has been reported in small amounts 

 in cultures oiFusarium spp. (Table 1), but the criteria of identification 

 were not wholly satisfactory. Using color tests and copper reduction 

 as criteria, Bernhauer and Bockl (51) found that most strains of 

 Aspergillus niger form tartrate during incubation of preformed 

 mycellium with ethanol. The problem merits study with the more 

 sensitive methods now available for isolation and determination of 

 acids. 



Glyoxylic acid (OHC — COOH), often accompanied by glycolic acid 

 (HOCH 2 — COOH), is formed in traces during carbohydrate break- 

 down by some fungi (Table 1); it has also been reported as being 

 formed during the metabolism of acetate (55, 125, 403), ethanol (136), 

 and citrate (125). It should be noted that substances giving the color 

 reactions for glyoxylic acid are found in sterile autoclaved culture 

 media (157); it has not always been clear that adequate controls have 

 been included in experiments on the occurrence of glyoxylate. 



Glyoxylate has been proposed as an intermediate in the oxidative 

 formation of oxalate from acetate by the following reactions (403): 



Acetate — » glycolate — > glyoxylate -» oxalate (3) 



It is not yet certain that these reactions occur. The fact that glyoxylic 

 and glycolic acids replace glycine in the nutrition of a mutant of 

 Nenrospora crassa (566) suggests a second pathway for their utilization 

 and formation. Finally, the ability of fungi under some conditions 

 to split isocitrate to succinate and glyoxylate and to oxidize glycolate 

 to glyoxylate has been shown unequivocally (405). Glyoxylate is also, 

 it should be noted, a product of the action of allantoicase (Chapter 8). 



