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Question: a mechanism of how alkaline phosphatase acts on phosphate monoesters...

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A mechanism of how alkaline phosphatase acts on phosphate monoesters was proposed by Holtz and Kantrowitz (see mechanism at end of report). The structure of PNPP is to the right, circle the oxygen(s) in PNPP that coordinate with Arg166 when the enzyme-substrate complex is formed. Use the space below if you need to clarify your answer. 2. a) PNPP b)In the reaction of alkaline phosphatase and PNPP (see Holtz and Kantrowitz mechanism at end of report), the PNPP enters the active site of the enzyme. Circle (in the reaction below) the Product which leaves first from the active site alkaline phophieteseNa Q Na Na
K M. Holiz, ER KantrowiFEBS Letters 462 (1999) 7-11 RE ROP Znj Arg166 ROP Ser102 Ser102 PO; POİ RO Arg 166 Arg166 Ser102 E-r, Fig. I. Proposed mechanism of two-metal ion catalysis in the hy- drolysis of phosphate monoesters by AP. Formation of the enzyme substrate complex (E-ROP) involves coordination of the ester oxy- gen to Zn and additional interactions between the non-bridging oxygen atoms of the substrate, and Zng and the guanidinium group of Arg-166. Ser-102 occupies the position opposite the leaving group. Upon formation of the covalent E-P intermediate, phosphate moves slightly into the active site cavity maintaining interactions to both Arg-166 and the zine ions. At alkaline pH, a nucleophilic hy- droxide coordinated to Zni (identified as wat) attacks the covalent E-P intermediate forming the non-covalent E:P complex. The slow dissociation of phosphate from this complex is rate-limiting under alkaline conditions. The geometries of the EP complex and the E-P intermediate come from the X-ray crystal structures of the native and Cd-substituted enzymes, respectively [23] Hydrogen atoms, the magnesium ion, and the ligands to Zni and Zny are not shown.
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