Immobilized purine nucleoside phosphorylase from Aeromonas hydrophila as an on-line enzyme reactor for biocatalytic applications

• Purine nucleoside phosphorylase from Aeromonas hydrophila was immobilized onto the surface of open tubular capillaries.
• The bioreactor has been coupled to an analytical column for on-line quantification of the product and unreacted substrate.
• The resulting bioreactor has been characterized by the determination of kinetic constants.
• The AhPNP-IMER was used for the evaluation of the substrate specificity toward different nucleoside libraries.

We described the development of a biochromatographic system which uses a purine nucleoside phosphorylase from Aeromonas hydrophila (AhPNP) for the evaluation of the substrate specificity on nucleoside libraries. AhPNP has been covalently immobilized on a fused silica Open Tubular Capillary (OTC) via Schiff base chemistry. The resulting bioreactor has been characterized by the determination of kinetic constants (Km and Vmax) for a natural substrate (inosine) and then assayed versus all natural purine (deoxy)ribonucleosides and a small library of 6-substituted purine ribosides. Characterization of the bioreactor has been carried out through a bidimensional chromatographic system with the sample on-line transfer from the bioreactor to the analytical column for the separation and quantification of substrate and product. Comparison with the soluble enzyme showed that the AhPNP-based bioreactor is reliable as the same ranking order, with respect to the standard activity assay, was obtained. The stability of the IMER was also assessed and the system was found to be stable up to 60 reactions.