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Development of enzymes of glycerol metabolism in human fetal liver
Insights
Human fetal, neonatal, and infant liver can metabolize glycerol. Key enzyme activity, glycerol kinase, remained constant, but its location shifted from particulate to cytoplasmic after birth, impacting glycerol metabolism during development.
Area of Science:
- Biochemistry
- Developmental Biology
- Human Physiology
Background:
- Glycerol metabolism is crucial for energy homeostasis.
- Understanding developmental changes in liver enzyme activity is essential for assessing metabolic adaptation.
Purpose of the Study:
- To investigate the activity and subcellular distribution of key glycerol metabolism enzymes in human liver across different developmental stages.
- To characterize kinetic properties and developmental trends of glycerol kinase, cytoplasmic glycerol-3-phosphate dehydrogenase, and mitochondrial glycerol-3-phosphate dehydrogenase.
Main Methods:
- Enzyme activity assays were performed on liver samples from human fetuses (18 weeks to term), neonates (1-3 days), and infants (up to 2 years).
- Kinetic parameters (Km) and subcellular localization of enzyme activities were analyzed.
Main Results:
- Glycerol kinase specific activity was consistent across fetal, neonatal, and infant stages, but its subcellular distribution shifted from particulate (fetal) to cytoplasmic (postnatal).
- Particulate glycerol kinase exhibited a higher Km for glycerol compared to cytoplasmic activity.
- Cytoplasmic glycerol-3-phosphate dehydrogenase activity was low in fetuses and increased to adult levels during infancy, while mitochondrial glycerol-3-phosphate dehydrogenase activity increased postnatally.
Conclusions:
- Human fetal, neonatal, and infant liver possess the enzymatic machinery for glycerol metabolism.
- Developmental changes in the subcellular localization and activity of glycerol-metabolizing enzymes suggest significant metabolic adaptations occurring around birth and during early infancy.
Abstract:
The activities of three key enzymes of glycerol metabolism were measured in liver samples from 37 human fetuses ranging in gestational age from 18 weeks to term, from neonates (1-3 days) and from infants to 2 years. Glycerol kinase specific activity was constant throughout the period of fetal development examined, and was comparable to that measured in neonates and infants. However, the subcellular distribution of the activity changed markedly, being predominantly particulate in fetal samples and cytoplasmic in postnatal samples. The particulate activity had an elevated Km for glycerol. Cytoplasmic glycerol-3-phosphate dehydrogenase activity was very low in the fetal period, and then rose to adult levels during infancy. There were no kinetic differences between the fetal and postnatal activities. Mitochondrial glycerol-3-phosphate dehydrogenase activity rose somewhat after birth to near adult levels. The data indicate that glycerol can be metabolized by human fetal, neonatal and infant liver.