Pyruvate carboxylase defect: metabolic studies on cultured skin fibroblasts

Oxidative studies using a number of radioactive carbon-labelled substrates on intact cultured skin fibroblasts from a patient with pyruvate carboxylase deficiency revealed dysfunction of the Krebs cycle. The suppression of CO2 production from aspartate but not glutamine strongly suggests that the defective function lies in the aspartate-malate shuttle. Furthermore, there is an unusual dependence on glutamine for the maintenance of growth of the patient's cells compared to normal cells. Glutamine could not be replaced by aspartate supplementation. A secondary defect resulting in accumulation of lipid material was also demonstrated in this study. It is speculated that the intracellular level of oxaloacetate may also be diminished in the patient's cells. Oxaloacetate is primarily generated by the carboxylation of pyruvate catalysed by pyruvate carboxylase.