Summary: Cell-free extracts of an itaconic acid producing strain of contained NADP-dependent isocitrate dehydrogenase activity but no NAD-dependent activity was detected. During the acid-producing phase the activity of the NADP-linked enzyme fell to one-eighth of its value during the growth phase, whereas citrate synthase activity increased. Intact mitochondria were isolated from growth and production phase mycelium. The preparation from the growth phase oxidized exogenous NADH and all tricarboxylic acid cycle intermediates tested. That from the production phase oxidized tricarboxylic acid cycle intermediates at a reduced rate but exogenous NADH oxidation remained high. [2-C]Acetate was incorporated into itaconic acid and over 90% of the incorporated radioactivity was located in the methylene carbon. [1-C]-Acetate was a poorer precursor and did not preferentially label the methylene carbon. These results support the view that itaconic acid biosynthesis in occurs by decarboxylation of aconitic acid, the latter produced by the normal reactions of the tricarboxylic acid cycle.


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