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Postnatal development of peroxisomal and mitochondrial enzymes in rat liver
Insights
This study tracks changes in rat liver organelle enzyme activity from prenatal to adult stages. Mitochondrial beta-oxidation shows the most significant developmental changes, impacting overall fatty acid metabolism.
Area of Science:
- Biochemistry
- Cell Biology
- Developmental Biology
Background:
- Subcellular organelles, including peroxisomes and mitochondria, play crucial roles in cellular metabolism.
- Understanding the developmental changes in these organelles and their enzyme activities is vital for comprehending liver function maturation.
Purpose of the Study:
- To investigate the developmental changes in peroxisomal and mitochondrial enzyme activities in rat liver from prenatal stages to adulthood.
- To quantify the contributions of peroxisomal versus mitochondrial fatty acid beta-oxidation throughout development.
Main Methods:
- Separation of subcellular organelles from rat livers across various developmental ages using sucrose gradients.
- Assay of enzyme activities including fatty acid beta-oxidation, catalase, glycerol-3-phosphate dehydrogenase, urate oxidase, and glutamate dehydrogenase.
- Determination of organelle densities to confirm separation and monitor structural changes.
Main Results:
- Mitochondrial density changed significantly postnatally, while peroxisomal density remained constant.
- Enzyme activities, particularly mitochondrial glutamate dehydrogenase and peroxisomal urate oxidase, peaked at specific developmental stages.
- Fatty acid beta-oxidation showed dynamic changes, with mitochondrial activity decreasing post-weaning, leading to a relative increase in peroxisomal contribution.
Conclusions:
- Rat liver organelle enzyme activities undergo substantial developmental regulation, with distinct patterns for peroxisomal and mitochondrial enzymes.
- Mitochondrial beta-oxidation exhibits greater developmental plasticity than peroxisomal beta-oxidation, significantly influencing overall fatty acid metabolism shifts.
- Catalase activity shows developmental redistribution, with peroxisomal contribution decreasing as supernatant activity increases in adult rats.
Abstract:
Subcellular organellles from livers of rats three days prenatal to 50 weeks postnatal were separated on sucrose gradients. The peroxisomes had a constant density of 1.243 g/ml throughout the life of the animal. The density of the mitochondria changed from about 1.236 g/ml at birth to a constant value of 1.200 g/ml after two weeks. The peroxisomal and mitochondrial fatty acid beta-oxidation and the peroxisomal and supernatant activities of catalase and glycerol-3-phosphate dehydrogenase were measured at each age, as well as the peroxisomal core enzyme, urate oxidase, and the mitochondrial matrix enzyme, glutamate dehydrogenase. All of these activities were very low or undetectable before birth. Mitochondrial glutamate dehydrogenase and peroxisomal urate oxidase reached maximal activities per g of liver at two and five weeks of age, respectively. Fatty acid beta-oxidation in both peroxisomes and mitochondria and peroxisomal glycerol-3-phosphate dehydrogenase exhibited maximum activities per g of liver between one and two weeks of age before weaning and then decreased to steady state levels in the adult. Peroxisomal beta-oxidation accounted for at least 10% of the total beta-oxidation activity in the young rat liver, but became 30% of the total in the liver of the adult female and 20% in the adult male due to a decrease in mitochondrial beta-oxidation after two weeks of age. The greatest change in beta-oxidation was in the mitochondrial fraction rather than in the peroxisomes. At two weeks of age, four times as much beta-oxidation activity was in the mitochondria as in the peroxisomal fraction. Peroxisomal glycerol-3-phosphate dehydrogenase activity accounted for 5% to 7% of the total activity in animals younger than one week, but only 1% to 2% in animals older than one week. Up to three weeks of age, 85% to 90% of the liver catalase was recovered in the peroxisomes. The activity of peroxisomal catalase per g of rat liver remained constant after three weeks of age, but the total activity of catalase further increased 2.5- to 3-fold, and all of the increased activity was in the supernatant fraction.