Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: ayesha on 06/02/2010 09:32:37
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how does the concentration of chloride ions affect the rate at which salivary amylase hydrolysis starch?
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Wikipedia says only that for ptyalin, the presence of chloride and bromide ions are the most effective, among anions and activators:
Optimum conditions for ptyalin
Optimum pH - 5.6–6.9
Human body temperature - 37 °C
Presence of certain anions and activators:
Chloride and bromide - most effective
Iodide - less effective
Sulfate and phosphate - least effective
http://en.wikipedia.org/wiki/Alpha-Amylase
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how the presence of chloride ions are effective?
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how the presence of chloride ions are effective?
Don't know, sorry.
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Chloride is the allosteric effector of vertebrate pancreatic and salivary α-amylases and of the bacterial α-amylase from Alteromonas haloplanctis. Activation experiments of A. haloplanctis α-amylase by several monovalent anions show that a negative charge, not restricted to that of Cl−, is essential for the amylolytic reaction. Engineering of the chloride binding site reveals that a basic residue is an essential component of the site. The mutation K337R alters the Cl−-binding properties, whereas the mutation K337Q produces an active, chloride-independent enzyme. Comparison of the Kd values for Cl− in three homologous α-amylases also indicates that the binding affinity is dependent on the chloride coordination mode by this basic residue. Analysis of substrate and chloride binding according to the allosteric kinetic model shows that the chloride effector is not involved in substrate binding. By contrast, the pH dependence of activity and experiments of chemical modifications and Ca2+ inhibition show that the chloride ion is responsible for the pKa shift of catalytic groups and interacts with active site carboxyl groups.
http://www.jbc.org/content/271/39/23836.full?sid=5ba058d6-74ce-4e28-ae2d-5368d9f2cd68