Salivary Amylase Is Activated By Which Ion?

Chloride ions. 

For salivary amylase, amongst anions and activators, the presence of chloride and bromide ions is the most effective. 

Amylase is an enzyme found in the saliva of humans and some other mammals. Salivary amylase or ptyalin catalyzes the hydrolysis of starch into sugars. Chloride is the allosteric effector of salivary ∝-amylases, vertebrate pancreatic, and of the bacterial ∝-amylase from Alteromonas haloplanctis. A few monovalent anions were used to carry out activation experiments of Alteromonas haloplanctis, which depicted that a negative charge is required for the amylolytic reaction. Furthermore, the structures of the chloride binding site disclose that a basic residue is an important component of the site. A brief comparison of the kd values for Cl in three homologous ∝-amylases depicted that the binding affinity depends on the chloride coordination mode by that basic residue. 

As per the allosteric kinetic model, careful analysis of chloride binding and substrate reveal that the chloride effector has no role in substrate binding. But, the experiments of chemical modifications, pH dependence of activity, and calcium ions inhibitions demonstrate that chloride ions are responsible for the pKa shift of the catalytic groups and interaction with active site carboxyl groups. 

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