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Comparative development of the pyruvate dehydrogenase complex and citrate synthase in rat brain mitochondria
Insights
Pyruvate dehydrogenase complex (PDHC) activity significantly increases in developing rat brains, primarily due to more PDHC protein per mitochondrion. This specific synthesis may be vital for acquiring neurological competence.
Area of Science:
- Biochemistry
- Neuroscience
- Developmental Biology
Background:
- The pyruvate dehydrogenase complex (PDHC) is crucial for cellular energy metabolism.
- Understanding PDHC's role in brain development is key to understanding neurological competence.
Purpose of the Study:
- To investigate the developmental changes in pyruvate dehydrogenase complex (PDHC) activity and protein content in the rat brain.
- To determine the mechanisms underlying the increase in PDHC activity during postnatal development.
Main Methods:
- Enzyme activity assays of PDHC and citrate synthase in isolated rat brain mitochondria.
- Measurement of PDHC and citrate synthase protein levels using enzyme-linked immunoadsorbent assays.
- Analysis of PDHC subunit dephosphorylation to assess enzyme activation.
Main Results:
- PDHC activity markedly increased between days 10 and 15 post partum, reaching 60% of the difference between fetal and adult levels.
- Increased PDHC protein content correlated with enzyme activity, suggesting enhanced synthesis.
- The primary driver of increased PDHC activity was a higher amount of PDHC per mitochondrion, not just increased mitochondrial numbers.
Conclusions:
- The developmental surge in rat brain PDHC activity is mainly due to increased synthesis of PDHC protein per mitochondrion.
- This specific increase in PDHC synthesis, rather than general mitochondrial growth, may be critical for the acquisition of neurological competence.
- PDHC plays a significant role in shifts in respiratory substrate utilization during brain development.
Abstract:
The enzyme activity of the pyruvate dehydrogenase complex (PDHC) was measured in mitochondria prepared from developing rat brain, before and after steady-state dephosphorylation of the E1 alpha subunit. A marked increase in dephosphorylated (fully activated) PDHC activity occurred between days 10 and 15 post partum, which represented approx. 60% of the difference in fully activated PDHC activity measured in foetal and adult rat brain mitochondria. There was no detectable change in the active proportion of the enzyme during mitochondrial preparation nor any qualitative alteration in the detectable catalytic and regulatory components of the complex, which might account for developmental changes in PDHC activity. The PDHC protein content of developing rat brain mitochondria and homogenates was measured by an enzyme-linked immunoadsorbent assay. The development of PDHC protein in both fractions agreed closely with the development of the PDHC activity. The results suggest that the developmental increase in PDHC activity is due to increased synthesis of PDHC protein, which is partly a consequence of an increase in mitochondrial numbers. However, the marked increase in PDHC activity measured between days 10 and 15 post partum is mainly due to an increase in the amount of PDHC per mitochondrion. The development of citrate synthase enzyme activity and protein was measured in rat brain homogenates and mitochondria. As only a small increase in citrate synthase activity and protein was detected in mitochondria between days 10 and 15 post partum, the marked increase in PDHC protein and enzyme activity may represent specific PDHC synthesis. As several indicators of acquired neurological competence become apparent during this period, it is proposed that preferential synthesis of PDHC may be crucial to this process. The results are discussed with respect to the possible roles played by PDHC in changes of respiratory-substrate utilization and the acquisition of neurological competence occurring during the development of the brain of a non-precocial species such as the rat.