Activating the Phosphate Nucleophile at the Catalytic Site of Purine Nucleoside Phosphorylase: A Vibrational Spectroscopic Study

Difference Raman and FTIR studies complemented by vibrational analysis based on ab initio calculations show that the dianionic phosphate in the PNP·ImmH·PO4 complex is forced into a unique bonding arrangement in which one of the PO bonds is greatly polarized by enzyme active site interactions, such that it resembles a PO bond that is about one-quarter of the way toward forming a bridging P−O−C single P−O bond.