114 CARBON METABOLISM III 



The higher fatty acids, above acetic, are considered integrally with 

 the metabolism of lipids. 



Oxalic Acid. Oxalic acid is a common metabolic product of fungi 



(Table 1) especially ol the Agaricales. Species of Penicillium and 

 Aspergillus accumulate the largest amounts but substantial oxalate 

 production occurs in a few other fungi, e.g., Sclerotium delphinii 

 (414). Sporophores of basicliomycetes often contain oxalate (17, 575, 

 576). 



The physiology of oxalate formation deserves more study. The 

 acid is formed from various carbon sources (49); the most favorable 

 cultural conditions include a high carbohydrate concentration, ade- 

 quate aeration (49, 545), a limited supply of inorganic nutrients (129, 

 447), and, most important, a relatively high initial pH (46, 49, 299). 

 The enzymatic basis of the pH requirement has been elucidated by 

 Shimazono (470): at low pH an enzyme, oxalic acid decarboxylase, is 

 formed and converts oxalate to formate and carbon dioxide. This 

 finding suggests, for the higher basicliomycetes at least, that oxalate 

 is a normal metabolite and accumulates under conditions of an 

 enzyme deficiency. Cultures of Aspergillus niger utilize oxalate pro- 

 vided that the pH is below 5.5 (27). 



In Corticium centrijugutn oxalic acid production is increased by a 

 growth-limiting deficiency of thiamine (391). This relation is con- 

 sistent with the general view that oxalic and other acids are formed 

 maximally when available carbon cannot be used for growth. 



The biochemical origin of oxalic acid has been investigated rather 

 frequently, but none of the pathways proposed has been proved (4, 5, 

 403). Recent results with isotopic carbon are consistent with the 

 origin of oxalate from oxalacetate (88, 138a, 201, 338). The possibility 

 that glycine, which in different organisms is metabolically related to 

 other 2-carbon compounds, is involved has not yet been explored. 

 Progress on the problem depends on the preparation of active non- 

 cellular preparations. 



Itaconic and Itatartaric Acids. Itaconic acid was discovered by 

 Kinoshita (314, 315) to be formed by a strain which he designated 

 Aspergillus itaconicus n. sp. This strain has lost its capacity to form 

 more than small amounts of the acid, but strains of Aspergillus terreus 

 have been found to produce large yields (105, 384). Other strains of 

 the same species form no itaconate, and ultraviolet-induced mutants 

 yield more or less acid than the parent culture (349). 



The optimum conditions for itaconic acid formation are rather 

 different from those which give best growth of the organism (348, 350, 



