Multiple molecular forms of mouse liver arginase.

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Hepatic arginase (L-arginine amidinohydrolase, EC 3.5.3.1) is a key enzyme in urea and amino acid metabolism.
• Arginase exists as an oligomer, typically composed of three or four subunits.
• Understanding subunit heterogeneity is crucial for elucidating enzyme function and regulation.

Purpose of the Study:

• To investigate the heterogeneity in size and charge of mouse liver arginase subunits.
• To identify the molecular basis for observed subunit variations.
• To determine if different subunit forms represent distinct proteins or variants.

Main Methods:

• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting to analyze subunit molecular weights.
• Two-dimensional SDS-PAGE to assess subunit charge heterogeneity (isoelectric points).
• Limited proteolysis, peptide mapping, and amino acid analysis to compare subunit structures.

Main Results:

• Two distinct arginase subunit molecular weights (approximately 35,000 and 38,000 Da) were identified in mouse liver cytosol and purified preparations.
• Both subunit sizes exhibited multiple ionic forms, ranging from basic (pI 7.8–9.1) to acidic (pI 5.8–6.4).
• Limited tryptic proteolysis removed molecular weight differences without altering isoelectric points or activity; peptide maps and amino acid analyses indicated high similarity between subunits, suggesting a ~3000 Da neutral peptide accounts for the size difference.

Conclusions:

• Mouse liver arginase subunits display significant heterogeneity in both molecular weight and charge.
• These variations arise from the presence of a neutral peptide, leading to different sized subunits.
• The findings indicate that the observed heterogeneity represents multiple forms of the same arginase protein, not distinct enzymes.