ATP-AMP phosphotransferase from Paracoccus denitrificans

Area of Science:

• Biochemistry
• Enzymology
• Microbial Physiology

Background:

• Adenylate kinase (AK) plays a crucial role in cellular energy metabolism by interconverting adenine nucleotides.
• Understanding the properties of AK from diverse microbial sources like Paracoccus denitrificans can provide insights into its evolutionary conservation and functional variations.

Purpose of the Study:

• To extract and purify adenylate kinase from Paracoccus denitrificans.
• To characterize the biochemical and biophysical properties of the purified enzyme.
• To compare the P. denitrificans adenylate kinase with known adenylate kinase types.

Main Methods:

• Enzyme extraction via toluene treatment.
• Purification using sequential column chromatography (DEAE-cellulose, Matrex-Blue A, Sephadex G-75).
• Homogeneity assessment by SDS-PAGE and enzyme kinetics.
• Crystallization and characterization of kinetic parameters (Km, dissociation constants).
• Analysis of structural features (sulfhydryl groups, disulfide bonds) and stability.

Main Results:

• Adenylate kinase was purified 370-fold with a specific activity of 554 U/mg.
• The enzyme exhibited specific affinities for adenine nucleotides with low dissociation constants.
• Characterization revealed a molecular weight of 22,000, pI of 4.7, and optimal activity at pH 7.5-8.0.
• The enzyme possesses two free sulfhydryl groups, lacks disulfide bonds, and is stable at neutral pH and below 44°C.
• Kinetic properties and structural features align with muscle-type (cytoplasmic) adenylate kinase.

Conclusions:

• Purified adenylate kinase from P. denitrificans is a stable enzyme with characteristics similar to muscle-type adenylate kinase.
• Its specific substrate affinities and structural features provide valuable data for comparative enzymology.
• The findings contribute to the understanding of adenylate kinase diversity and function in prokaryotes.