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Dietary alteration of translatable mRNA sequences coding for rat liver pyruvate kinase
Abstract:
Poly(A+) RNA (RNA containing a polyadenylic acid sequence) was isolated from individual livers of rats fed standard lab chow, fasted, or fasted and refed a high carbohydrate diet. The level of functional mRNA coding for pyruvate kinase was assayed using a rabbit reticulocyte in vitro translation system. The total 35S incorporation into newly synthesized liver pyruvate kinase was measured and compared to 35S incorporation into albumin, total trichloroacetic acid-precipitated proteins, and released polypeptide chains. The relative level of mRNA coding for liver pyruvate kinase decreases almost 60% upon fasting and increases approximately 15-fold upon refeeding with a high carbohydrate diet for 24 h. These observed changes in the amount of mRNA coding for liver pyruvate kinase agree with the previously reported changes in the relative rates of liver pyruvate kinase synthesis measured in vivo during these dietary stresses. Thus, it is suggested that the alterations in the amount of pyruvate kinase in liver in response to these dietary stresses primarily result from alteration in the amount of functional mRNA coding for the enzyme.
Insights
Fasting reduces liver pyruvate kinase mRNA by 60%, while refeeding with carbohydrates increases it 15-fold. Dietary changes primarily alter pyruvate kinase levels by changing its messenger RNA (mRNA) amount.
Area of Science:
- Biochemistry
- Molecular Biology
- Physiology
Background:
- Pyruvate kinase is a key enzyme in glycolysis.
- Dietary conditions significantly impact liver metabolism and enzyme synthesis.
Purpose of the Study:
- To investigate the effect of fasting and carbohydrate refeeding on the level of functional mRNA coding for liver pyruvate kinase.
- To determine if changes in mRNA levels correlate with previously observed changes in pyruvate kinase synthesis rates.
Main Methods:
- Isolation of poly(A+) RNA from rat livers under different dietary conditions (standard chow, fasting, fasted and refed).
- Assay of functional mRNA for pyruvate kinase using an in vitro translation system.
- Measurement of 35S incorporation into newly synthesized pyruvate kinase and other proteins.
Main Results:
- Fasting decreased liver pyruvate kinase mRNA by approximately 60%.
- Refeeding with a high-carbohydrate diet for 24 hours increased pyruvate kinase mRNA by about 15-fold.
- Changes in mRNA levels closely paralleled previously reported in vivo synthesis rates.
Conclusions:
- Alterations in liver pyruvate kinase levels in response to dietary stress are primarily mediated by changes in the amount of functional mRNA.
- This suggests post-transcriptional regulation plays a crucial role in adapting enzyme levels to nutritional status.