Subject: Does all starch dissapear when it is hydrolysed by amylase enzyme?

Hello,
      I read that enzyme-catalysed reactions are reversible reactions. 

      So, if the reaction is allowed to proceed in a test-tube, an equilibrium 
should be reached in which there is some reactant left (unlike in a cell, where 
the products are constantly being used up).

      This sounds weird, especially when considering the hydrolysis of starch by 
amylase. If some starch is mixed with amylase and the reaction is allowed to 
occur and then iodine is added, there is NO BLUE-BLACK colouration, indicating 
the absence of starch and hence COMPLETE hydrolysis into maltose. But this 
should not have been the case with a REVERSIBLE reaction; some reactant (starch) 
should be left and a blue-black colour SHOULD be obtained.

      Actually, my teacher told me that enzyme-catalysed reactions are 
irreversible, but I kept on arguing with her since I found the opposite in the 
book Biological Science, by Taylor, Green and Stout. She gave me the observation 
with starch and amylase as a proof of her stance and I could not refute her 
point.
      
      I would be very much obliged to anyone who could help me out.
Thanks,
Irshaad.

Re: Does all starch dissapear when it is hydrolysed by amylase enzyme?