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Ontogeny of cyclic AMP-dependent protein phosphokinase during hepatic development of the rat
Insights
This study tracked protein kinase and cyclic AMP-binding activity in developing rat liver. Protein kinase activity peaked early post-birth, while cyclic AMP-binding activity varied by fraction and age.
Area of Science:
- Biochemistry
- Developmental Biology
- Molecular Biology
Background:
- Protein kinases regulate cellular processes through phosphorylation.
- Cyclic AMP (cAMP) is a crucial second messenger involved in signal transduction.
- Understanding the ontogeny of these enzymes is vital for comprehending liver development.
Purpose of the Study:
- To investigate the developmental changes in protein kinase and cAMP-binding activity in rat liver subcellular fractions.
- To determine the relationship between cAMP-binding activity and cAMP-dependent protein kinase activity during development.
Main Methods:
- Analysis of protein kinase and cAMP-binding activity in nuclear, microsomal, lysosomal-mitochondrial, and soluble liver fractions from prenatal to adult male rats.
- Use of histone F1 as a substrate for protein kinase assays.
- Activation of latent microsomal protein kinase activity using Triton X-100.
Main Results:
- Protein kinase activity in all fractions peaked at 2 days post-birth and returned to prenatal levels by 10 days.
- Latent microsomal protein kinase activity was highest prenatally and at birth, declining postnatally.
- Cyclic AMP-binding activity showed distinct developmental patterns across fractions, peaking in cytosol, microsomes, and lysosome-mitochondria at 10-11 days, and in nuclei prenatally.
Conclusions:
- Protein kinase activity undergoes significant developmental regulation in rat liver, with a distinct early postnatal peak.
- Cyclic AMP-binding activity exhibits complex developmental alterations independent of cAMP-dependent protein kinase activity.
- The observed cAMP-binding activity may not directly reflect developmental changes in the regulatory subunit of cAMP-dependent protein kinase.
Abstract:
The ontogeny of protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) and cyclic AMP-binding activity in subcellular fractions of liver was examined during prenatal and postnatal development of the male rat. 1. Protein kinase activity and cyclic AMP-binding activity were found in the nuclear, microsomal, lysosomal-mitochondrial, and soluble liver fractions. 2. The protein kinase activity of the soluble (105 000 X g supernatant) fraction measured with histone F1 as substrate was stimulated by cyclic AMP. Cyclic AMP did not stimulate the protein kinase activity of the particulate fractions. 3. The protein kinase activity of all subcellular fractions increased rapidly from the activity observed in prenatal liver (3-4 days before birth) to reach maximal activity in 2-day-old rats. Thereafter, the protein kinase activity declined more slowly and regained the prenatal levels at 10 days after birth. 4. Considerable latent protein kinase activity was associated with liver microsomal fractions which could be activated by treatment of microsomes with Triton X-100. The latent microsomal protein kinase activity was highest in prenatal liver, at the time of birth, and 2 days after birth. During the subsequent postnatal development the latent microsomal protein kinase activity gradually declined to insignificantly low levels. 5. During the developmental period examined (4 days before birth to age 60-90 days) marked alterations of the cyclic AMP-binding activity were determined in all subcellular fractions of rat liver. In general, cytosol, microsomal, and lysosomal-mitochondrial cyclic AMP-binding activity was highest in 10-11 day-old rats. Nuclear cyclic AMP-binding activity was highest 3-4 days before birth and declined at birth and during the postnatal period. There was no correlation between the developmental alteration of cyclic AMP-binding activity and cyclic AMP dependency of the protein kinase activity in any of the subcellular fractions. This suggests that the measured cyclic AMP-binding activity does not reflect developmental alterations of the cyclic AMP-binding regulatory subunit of cyclic AMP-dependent protein kinase.