Interactions of calf spleen purine nucleoside phosphorylase with formycin B and its aglycone - spectroscopic and kinetic studies |
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Authors: | Wierzchowski Jacek Iwanska Beata Bzowska Agnieszka Shugar David |
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Affiliation: | Department of Biophysics, University of Warmia and Mazury, Olsztyn, Poland. jacek.wie@uwm.edu.pl |
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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. |
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