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. Author manuscript; available in PMC: 2008 Aug 27.
Published in final edited form as: Biochemistry. 2007 Apr 4;46(17):5038–5049. doi: 10.1021/bi700147b

Figure 1.

Figure 1

a) The relationship among BIE, V/K KIE, and intrinsic KIE using purine nucleoside phosphorylase (PNP) as a model. Ino = inosine, Hx = hypoxanthine, R1As = ribose 1-arsenate. b) Arsenolysis reaction catalyzed by purine nucleoside phosphorylase including the SN1-like transition state. Unlike the analogous phosphorolysis reaction, arsenolysis is irreversible due to the instability of the ribose 1-arsenate product, which rapidly hydrolyzes. N7 of the leaving group has been depicted as being protonated at the transition state, as this has been demonstrated to be a common mechanistic feature in PNP and other nucleoside phosphorylases and hydrolases (37).