Kinetic properties of Cellulomonas sp. purine nucleoside phosphorylase with typical and non-typical substrates: implications for the reaction mechanism.
Phosphorolysis catalyzed by Cellulomonas sp. PNP with typical nucleoside substrate, inosine (Ino), and non-typical 7-methylguanosine (m7Guo), with either nucleoside or phosphate (Pd) as the varied substrate, kinetics of the reverse synthetic reaction with guanine (Gua) and ribose-1-phosphate (R1P) as the varied substrates, and product inhibition patterns of synthetic and phosphorolytic reaction pathways were studied by steady-state kinetic methods. It is concluded that, like for mammalian trimeric PNP, complex kinetic characteristics observed for Cellulomonas enzyme results from simultaneous occurrence of three phenomena. These are sequential but random, not ordered binding of substrates, tight binding of one substrate purine bases, leading to the circumstances that for such substrates (products) rapid-equilibrium assumptions do not hold, and a dual role of Pi, a substrate, and also a reaction modifier that helps to release a tightly bound purine base.
Wielgus-Kutrowska
Beata
B
Department of Biophysics, Institute of Experimental Physics, University of Warsaw, Warsaw, Poland.
Bzowska
Agnieszka
A
D002384:Catalysis; D040143:Cellulomonas / Q000201:enzymology*; D006151:Guanosine / Q000031:analogs & derivatives / Q000737:chemistry; D007288:Inosine / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D010710:Phosphates / Q000737:chemistry; D011485:Protein Binding; D011683:Purine-Nucleoside Phosphorylase / Q000737:chemistry*; D013379:Substrate Specificity; D013696:Temperature
D010710:Phosphates; D006151:Guanosine; C016578:7-methylguanosine; D007288:Inosine; D011683:Purine-Nucleoside Phosphorylase