This is a conundrum. Iodine works as a stain
by binding onto the starch. Because it doesn't
bind onto other things as well, we can see where
the starch is. Unfortunately, this is the very
thing that will probably keep the starch from
being hydrolyzed by the enzyme amylase.
Enzymes only work on specific stuff
(substrates) because only specific molecules
fit into the active sites of the molecule. With
iodine stuck to the starch, the starch is unlikely
to fit into those binding sites. Whether the
enzyme will still work depends on what part of the
starch sticks to the stain and what part of the
starch fits into the enzyme. I've never tried
it myself, but I suspect the iodine would
interfere with the shape of the starch enough to
make a big difference.
I assume that you want to test for the presence
of starch, then see if you can hydrolyze it. My
suggestion is to take a sample of your material,
test that for the presence of starch, then add
your amylase to your material and test that
product for starch. By doing assays on just a
sample instead of the entire amount, you can get
around the problem.
I'd also be interested in how much loss of
amylase activity you get when you add the iodine.
Let me know what you find out.
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