Protein carboxyl methylation-demethylation system in developing rat livers.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Protein methylation is a crucial post-translational modification regulating various cellular processes.
• Understanding the enzymes involved in protein methylation and demethylation is essential for elucidating their biological roles.

Purpose of the Study:

• To investigate the activity and localization of protein carboxyl methyltransferase and protein methylesterase in rat liver cell fractions.
• To identify the specific proteins targeted by these methylation/demethylation enzymes.

Main Methods:

• Assaying enzyme activity in different rat liver cell fractions (cytosol, nucleoplasm).
• Using S-adenosylhomocysteine to inhibit methylation and assess demethylation.
• Measuring [3H]methanol generation to quantify protein methylesterase activity.
• Analyzing carboxyl-methylated proteins in vitro using hydroxylapatite and SDS-PAGE.

Main Results:

• Significant protein carboxyl methyltransferase activity was found in cytosol and nucleoplasm, peaking in young animals.
• Protein methylesterase activity was confirmed by the rapid decrease in carboxyl-methylated proteins upon methylation inhibition.
• Carboxyl-methylated proteins were primarily non-histone chromosomal proteins bound to DNA, with specific molecular weights identified (172K, 106K, 98K, 81K, 66K, 62K, 52K, 38K).

Conclusions:

• Rat liver cells possess active protein carboxyl methyltransferase and methylesterase systems.
• These enzymes play a role in the dynamic turnover of protein methyl esters.
• Non-histone chromosomal proteins are key targets for carboxyl methylation in the nucleus.