Substrate specificity and kinetic mechanism of purine nucleoside phosphorylase from Mycobacterium tuberculosis.
Purine nucleoside phosphorylase from Mycobacterium tuberculosis (MtPNP) is numbered among targets for persistence of the causative agent of tuberculosis. Here, it is shown that MtPNP is more specific to natural 6-oxopurine nucleosides and synthetic compounds, and does not catalyze the phosphorolysis of adenosine. Initial velocity, product inhibition and equilibrium binding data suggest that MtPNP catalyzes 2'-deoxyguanosine (2dGuo) phosphorolysis by a steady-state ordered bi bi kinetic mechanism, in which inorganic phosphate (P(i)) binds first followed by 2dGuo, and ribose 1-phosphate dissociates first followed by guanine. pH-rate profiles indicated a general acid as being essential for both catalysis and 2dGuo binding, and that deprotonation of a group abolishes P(i) binding. Proton inventory and solvent deuterium isotope effects indicate that a single solvent proton transfer makes a modest contribution to the rate-limiting step. Pre-steady-state kinetic data indicate that product release appears to contribute to the rate-limiting step for MtPNP-catalyzed reaction.
Ducati
Rodrigo G
RG
Centro de Pesquisas em Biologia Molecular e Funcional, Instituto Nacional de Ciência e Tecnologia em Tuberculose, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, RS, Brazil.
Santos
Diógenes S
DS
Basso
Luiz A
LA
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D011683:Purine-Nucleoside Phosphorylase / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013379:Substrate Specificity
D001426:Bacterial Proteins; D011994:Recombinant Proteins; D011683:Purine-Nucleoside Phosphorylase