Adenosine kinase from human liver

Area of Science:

• Biochemistry
• Enzymology

Background:

• Adenosine kinase (ATP: adenosine 5'-phosphotransferase, EC 2.7.1.20) plays a crucial role in purine metabolism.
• Understanding its properties is vital for various biological and therapeutic applications.

Purpose of the Study:

• To purify and characterize adenosine kinase from human liver.
• To investigate its kinetic properties, substrate specificity, and cofactor requirements.

Main Methods:

• Homogeneous purification of adenosine kinase from human liver.
• Enzyme activity assays, including kinetic analysis (Km) and substrate specificity.
• Physicochemical characterization using Sephadex G-100 gel filtration and SDS-PAGE.
• Structural comparison with other species via amino acid analysis and peptide mapping.

Main Results:

• Purified enzyme exhibited a specific activity of 6.3 mumol/min per mg protein with a yield of 55%.
• Molecular weight estimated at 40,000 Da. Catalyzed phosphorylation of adenosine, deoxyadenosine, arabinoadenosine, inosine, and ribavirin.
• Biphasic pH optimum (5.5 and 7.5-8.5), low Km for adenosine (0.15 µM), and inhibition at higher concentrations.
• Effective phosphate donors included ATP, dATP, GTP, and dGTP. Co2+ was a superior cofactor to Mg2+.
• Structural differences were noted compared to rabbit or rat adenosine kinase.

Conclusions:

• The study successfully purified and characterized human liver adenosine kinase.
• Detailed kinetic and cofactor data were established, offering insights into enzyme regulation.
• Observed structural variations suggest species-specific adaptations of adenosine kinase.