Aconitase

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Abstract
A method was worked out for the quantitative detn. of aconitic acid based on the catalytic hydrogenation of the double bond. The action of aconitase (the conversion of citric acid into cisaconitic acid and the reverse reaction) was studied in animal tissues. Aconitase was extracted with M/10 phosphate buffer pH 7.4 from minced pigeon breast muscle and other tissues. In tissue extracts aconitase converted about 75-85% of added cisaconitic acid into citric acid. Citric acid incubated with pigeon breast muscle extract formed 4% aconitic acid. The equilibrium was reached when the soln. contained about 16% isocitric acid (Martius), 4% cisaconitic acid and 80% citric acid. The pH optimum of aconitase in tissue extract was 7.4. In tissue slices the (apparent) optimum was 7.9. Aconitase was found in pigeon breast muscle, rat liver, kidney cortex, testis, brain cortex, lung, submaxillary gland, intestine, but not in red blood cells of the rat. Aconitase also occurred in cucumber seeds but its activity Was only 1.6% of that of pigeon breast muscle and no true equilibrium between cisaconitic, isocitric and citric acids was reached with cucumber seed extract.

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