A general method for the estimation of α-keto-acids, and its application to α-keto-acid metabolism in pigeon brain

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Abstract
Standard solns. of pyruvic, a-ketobutyric, a-ketovaleric and a-ketoglutaric acids at 28[degree]C evolved within 5 min. the theoretical vol. of CO2 corresponding to oxidative decarboxylation, when treated with excess acid KMnO4. With glyoxylic acid, the CO2 vol. exceeded 100%, due to further oxidation of formate produced. The bisulphite-binding figures for these [alpha]-keto-acids varied between 81-96.5%, so that this was judged to be an unsatisfactory general method of estimation. An accurate and reliable general method for determining 0.1-1.0 [mu] mol. [alpha]-keto-acid was developed, depending on the absorption intensity of the red-brown tint obtained on treating the corresponding 2:4-dinitrophenylhydrazone with excess NaOH. Absorption intensities were detd. with a Spekker Absorptiometer and purple color filter. The method was used to demonstrate directly that pyruvic acid a-ketobutyric acids are equally rapidly utilized by a washed prep. of minced pigeon brain.