Carbon dioxide fixation in animal tissues

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Abstract
The rate QCO2 of CO2 fixation by pyruvate to oxalocitrate for minced pigeon liver was 19 and for sheep kidney cortex 1.7 and for pigeon brain, rat liver, kidney cortex and muscle, guinea pig liver and brain, and sheep liver, heart, brain, spleen, pancreas and lung there was no CO2 fixation. In pigeon liver CO2 fixation by alpha-ketogluta-rate to citrate was rapid but ceased within a few mins. During the first minute QCO2 was 30. Pigeon breast muscle, guinea pig, rat and sheep liver, and sheep heart and kidney cortex all formed citrate while none was formed by guinea pig, rat or sheep brain, sheep spleen or rat and sheep testis. Citrate formation was dependent upon alpha-ketoglutarate, bicarbonate and CO2 concns. and was enhanced by fumarate, inhibited by L-lactate or NH4Cl. The inhibition of lactate, which also inhibited citrate formation from oxaloacetate and pyruvate, was partially reversed by L-glutamate.