Interactions of Calf Spleen Purine Nucleoside Phosphorylase with Formycin B and its Aglycone—Spectroscopic and Kinetic Studies

Abstract

Phosphorolysis of 7-methylguanosine by calf spleen purine nucleoside phosphorylase (PNP) is weakly inhibited, uncompetitively, by Formycin B (FB) with K _i = 100 μ M and more effectively by its aglycone (7KPP), IC₅₀ 35–100 μ M. In striking contrast, 7KPP inhibits the reverse reaction (synthesis of 8-azaguanosine from 8-azaguanine) competitively, with K _i ∼ 2–4 μ M. Formycin B forms only a weakly fluorescent complex with PNP, and 7KPP even less so, indicating that both ligands bind as the neutral, not anionic, forms. 7KPP is a rare example of a PNP non-substrate inhibitor of both the phosphorolytic and reverse synthetic pathways.

Keywords:

• Purine-nucleoside phosphorylase
• Formycin B
• inhibitor
• fluorescence
• ligand binding

Acknowledgments

This work was supported by grants from the State Committee for Scientific Research (KBN), 3P04A 024 25, and from the Polish Ministry of Science and Higher Education, grant N301 003 31/0042.

Notes

*Not determined.