Assay Report Card

ID: ALA3707659

Type: Binding

Description: Inhibition Assay: The inhibitor dissociation constants reported in Table 1 below are for phosphorolysis of inosine by PNP and were based on reaction rates measurements with different inhibitor concentrations. Reactions were started by addition of 0.05 ug of human or Plasmodium falciparum purine nucleoside phosphaorylase (HsPNP and PfPNP, respectively; final concentration 1.4 nM) to 1 mM inosine in 50 mM KPO4, pH=7.5 buffer with xanthine oxidase added to final concentration 60 mU/mL at 25 C. In the coupled assay, hypoxanthine formed by phosphorolysis of inosine was oxidized to uric acid and followed spectrophotometrically at 293 nm (extinction coefficient for uric acid epsilon(293)=12.9 mM-1). The dissociation constant for slow-onset tight-binding inhibitors was determined from reaction rates after slow onset inhibition had occurred according to the equation u =(kcat x S)/(Km(1+l/Kd)+S), where u  is the steady state reaction rate after the slow-onset inhibition period has reached equilibrium.

Organism: Plasmodium falciparum