Phosphoenolpyruvic carboxy kinase

Kidney Excretion and glu-coneogenesis Gluconeogenesis Free fatty acids, lactate, glycerol Glucose Glycerol kinase, phosphoenolpyruvate carboxy kinase... 

Oxaloacetate NADH Disappearance Malate Dehydrogenase Phosphoenolpyruvate Carboxy-kinase ... 

Park, E. A., Song, S-, Olive, M., and Koesler, W. J. (1997). CCAAT-cnhancen-binding protein a (C/EBPa) ia required for the thyroid hormone but not the retinoic acid induction of phosphoenolpyruvate carboxy kinase (PEPCK) gene transcription. Biocitem. /, 322,343-349. 

Pyruvate carboxylase is a mitochondrial enzyme, whereas the other enzymes of gluconeogenesis are present primarily in the cytoplasm. Oxaloacetate, the product of the pyruvate carboxylase reaction, must thus be transported to the cytoplasm to complete the pathway. Oxaloacetate is transported from a mitochondrion in the form of malate oxaloacetate is reduced to malate inside the mitochondrion by an NADH-linked malate dehydrogenase. After malate has been transported across the mitochondrial membrane, it is reoxidized to oxaloacetate by an NAD -linked malate dehydrogenase in the cytoplasm (Figure 16.26). The formation of oxaloacetate from malate also provides NADH for use in subsequent steps in gluconeogenesis. Finally, oxaloacetate is simultaneously decarboxylated and phospho-ry lated by phosphoenolpyruvate carboxy kinase to generate phosphoenol pyruvate. The phosphoryl donor is GTP. The GO2 that was added to pyruvate by pyruvate carboxylase comes off in this step. 

All of the steps in the breakdown of phosphoenolpyruvate carboxy-kinase in vitro occur at neutral pH and are not accelerated either by intact or by disrupted lysosomes. Yet a role for lysosomes cannot be eliminated, especially in the latter stages of enzyme catabolism, since the "denatured" enzyme might be selectively translocated into lysosomes after being attached to their outer surfaces. Nevertheless, it is most unlikely that lysosomes initiate the degradation process. Initiation is reduced by a combination of the ability of enzyme to maintain a stable conformation and by the high ratio of reduced to oxidized glutathione in cells. 

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