title: Interactions of calf spleen purine nucleoside phosphorylase with formycin B and its aglycone - spectroscopic and kinetic studies.
abstract: Phosphorolysis of 7-methylguanosine by calf spleen purine nucleoside phosphorylase (PNP) is weakly inhibited, uncompetitively, by Formycin B (FB) with Ki = 100 micro M and more effectively by its aglycone (7KPP), IC50 35-100 micro M. In striking contrast, 7KPP inhibits the reverse reaction (synthesis of 8-azaguanosine from 8-azaguanine) competitively, with Ki approximately 2-4 micro M. Formycin B forms only a weakly fluorescent complex with PNP, and 7KPP even less so, indicating that both ligands bind as the neutral, not anionic, forms. 7KPP is a rare example of a PNP non-substrate inhibitor of both the phosphorolytic and reverse synthetic pathways.
authors: Department of Biophysics, University of Warmia and Mazury, Olsztyn, Poland. jacek.wie@uwm.edu.pl
authors: Jacek
authors: J
authors: Wierzchowski
authors: Beata
authors: B
authors: Iwanska
authors: Agnieszka
authors: A
authors: Bzowska
authors: David
authors: D
authors: Shugar
mesh_terms: D000818:Animals; D002417:Cattle; D005573:Formycins / Q000737:chemistry / Q000378:metabolism*; D006151:Guanosine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism*; D011743:Pyrimidines / Q000737:chemistry / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013154:Spleen / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D005573:Formycins; D011743:Pyrimidines; D006151:Guanosine; C027180:7-ketopyrazolo(4,3-d)pyrimidine; C034561:formycin B; C013405:azaguanosine; C016578:7-methylguanosine; D011683:Purine-Nucleoside Phosphorylase