Der Mechanismus der Citronensäurebildung im Tierkörper im Zusammenhang mit dem Abbau der Brenztraubensäure

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Abstract
Oxalcitramalic acid was synthesized by adjusting a soln. of 13.5 g. oxalacetic acid and 8.8 g. pyruvic acid in 100 cc. HO to pH 9 with Na carbonate. After standing 18 hrs. at room temp., the soln. was acidified with H3PO4, extracted with ether, the ether extract concd. in vacuo, and crystalline oxalcitramalic obtained in 35% yield. The acid was readily oxidized to citric acid by H2O2. However, oxalcitramalic acid could not be an intermediate product in citric acid synthesis by the body, for if 3.5 g. of minced pig heart were added to a mixture of 105 mg. oxalacetic acid and 70 mg. pyruvic acid aerobically, 22 mg. citric acid were synthesized. Under the same conditions, from 25 mg. oxalcitramalic acid, less than 1 mg. citric acid was obtained. If 25.5 mg. of a-keto-butyric acid were added to a mixture of 5 g. beef heart, 33 mg. oxalacetic acid and 22 mg. pyruvic acid, the amt. of citric acid formed was 10 mg., while in the absence of the a-keto-butyric acid, the amt. of citric acid formed was 20 mg. Oxidation of pyruvic acid appeared to be the first step in the citric acid synthesis. The intermediate product may have been a 2C compound.

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