Molecular Basis of the Effects of Chloride Ion on the Acid−Base Catalyst in the Mechanism of Pancreatic α-Amylase

Pig pancreatic α-amylase (PPA), an enzyme belonging to the α-amylase family, is involved in the degradation of starch. Like some other members of this family, PPA requires chloride to reach maximum activity levels. To further explain the mechanism of chloride activation, a crystal of wild-type PPA s...

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Bibliographic Details
Published in:Biochemistry (Easton) 2005-03, Vol.44 (9), p.3194-3201
Main Authors: Qian, Minxie, Ajandouz, El Hassan, Payan, Françoise, Nahoum, Virginie
Format: Article
Language:English
Subjects:
alpha-Amylases - chemistry
alpha-Amylases - metabolism
Animals
Binding Sites
Catalytic Domain
Chlorides - chemistry
Chlorides - metabolism
Crystallization
Crystallography, X-Ray
Enzyme Activation
Hydrogen-Ion Concentration
Kinetics
Ligands
Pancreas - enzymology
Substrate Specificity
Swine
Trisaccharides - metabolism
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Summary:Pig pancreatic α-amylase (PPA), an enzyme belonging to the α-amylase family, is involved in the degradation of starch. Like some other members of this family, PPA requires chloride to reach maximum activity levels. To further explain the mechanism of chloride activation, a crystal of wild-type PPA soaked with maltopentaose using a chloride-free buffer was analyzed by X-ray crystallography. A conspicuous reorientation of the acid/base catalyst Glu233 residue was found to occur. The structural results, along with kinetic data, show that the acid/base catalyst is maintained in the active site, in an optimum position, pointing toward the scissile bond−atom, due to the presence of chloride ions. The present study therefore explains the mechanism of PPA activation by chloride ions.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi048201t