Re: How do chloride ions affect the activation of alpha amylase

Lindsey,
     Many enzymes exist in two states, an inactive and an active state.  
Usually these states differ in the conformation, or three-dimensional shape, 
of the enzyme.  The balance between these two states provides a means for 
regulating the activity of the enzyme, in effect, by turning it on or off.
     Often the switch that controls which state the enzyme is in is provided 
by a small molecule which binds to a receptor site somewhere on the surface 
of the enzyme.  Such a small molecule is called an allosteric effector.  For 
alpha-amylases from mammals, chloride ion is the allosteric effector.  These 
amylases have a binding site for chloride ion, which contains a positively 
charged amino acid residue (lysine, which at physiological pH is in the 
ammonium ion form).  This positive charge assists binding of the negatively 
charged chloride ion, and the size of the binding pocket excludes larger 
negative ions.
       Binding of chloride causes a conformational change to the amylase, 
switching it to the more active state.