Vanadate as a new substrate for nucleoside phosphorylases.

Area of Science:

• Biochemistry
• Enzymology
• Microbial Metabolism

Background:

• Nucleoside phosphorylases (NPs) are enzymes crucial for nucleoside metabolism.
• Orthovanadate is an inorganic phosphate analog with potential applications in enzymatic studies.
• Investigating novel substrates for NPs can reveal enzyme versatility and evolutionary adaptations.

Purpose of the Study:

• To determine if orthovanadate can serve as a substrate for various bacterial nucleoside phosphorylases.
• To identify exceptions to orthovanadate vanadolysis among different NP enzymes.
• To characterize the kinetics of nucleoside vanadolysis reactions.

Main Methods:

• Enzyme assays were performed using purified nucleoside phosphorylases from Escherichia coli, Shewanella oneidensis, Geobacillus stearothermophilus, and Halomonas chromatireducens AGD 8-3.
• Orthovanadate was used as a substrate to measure enzyme activity.
• Kinetic parameters, including kcat and Km, were determined for the vanadolysis reactions.

Main Results:

• Orthovanadate was successfully utilized as a substrate by nucleoside phosphorylases from E. coli, S. oneidensis, and G. stearothermophilus.
• Thymidine phosphorylase from the extremophilic bacterium Halomonas chromatireducens AGD 8-3 did not catalyze the vanadolysis of nucleosides.
• Kinetic parameters for the vanadolysis of nucleosides by the characterized NPs were successfully evaluated.

Conclusions:

• Nucleoside phosphorylases exhibit substrate specificity, with orthovanadate serving as a substrate for most tested enzymes.
• The thymidine phosphorylase from Halomonas chromatireducens AGD 8-3 represents a notable exception, lacking vanadolysis activity.
• This study provides insights into the substrate scope of nucleoside phosphorylases and their evolutionary divergence.