On malic acid and carboxylations in vivo in the liver of the chick embryo.

The rapid incorporation of labeled carbon dioxide into succinate of rat, liver in viva was previously demonstrated (1). In these experiments, the time of sacrifice after a single injection of the isotope was less than 30 minutes, and the experimental approach involved isolation of certain intermediates of the Krebs cycle. In whole homogenates (2), a similar rapid conversion of carbon dioxide to succinate was found, and the isotopic dilution of succinate formed in viva, by a mechanism other than the tricarboxylic acid cycle, was recently shown by Frohman and Orten (3). The possibility was considered that the conversion of labeled carbon dioxide to succinate might be more pronounced in some other biological system, for example in chick embryo liver. While a direct conversion of carbon dioxide to succinate was not supported in this embryo, a rapid incorporation of carbon dioxide into malate was evident. This dist’inguishes carbon dioxide fixation in vivo in chick embryo liver from that previously observed in the liver of the adult rat. Naturally occurring concentrations of malic acid reported here are more than 15 times greater than those found before in liver tissue (3, 4).