Abstract
Phosphopyruvate carboxylase [GTP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32] activity was detected in adult rat lung and was associated predominantly with the mitochondrial subcellular fraction. The enzyme was more active with Mn 2+ than Mg 2− and exhibited cofactor requirements similar to liver mitochondrial phosphopyruvate carboxylase. In the presence of Mn 2+ the Michaelis constant for both lung and liver mitochondrial phosphopyruvate carboxylase was 7.10 −5 M. While liver non-particulate phosphopyruvate carboxylase was inhibited by malate in the presence of Mg 2+, both lung and liver mitochondrial enzymes were unaffected. Similarly, with Mg 2+ as the bivalent cation only the lung and liver mitochondrial phosphopyruvate carboxylases were inhibited by AMP. The results indicate that the mitochondrial enzyme of rat lung has characteristics similar to those of the liver mitochondrial phosphopyruvate carboxylase.
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