Starch-iodine complex

Jon Monroe monroejd at jmu.edu
Sun Apr 5 14:10:28 EST 1998


>What is it? I have searched thru our chemical references and
>cannot find the formula for the starch-iodine complex. I am
>probably looking in the wrong place: under "starch" and "iodine".
>Inquiring junior college minds want to know! -NHarrison

Nancy and other inquiring minds;

My understanding is that amylose (the nearly unbranched form of starch)
forms a helix with six glucose units per turn (see Salisbury and Ross,
Plant Physiology 4th ed. page 247).  Iodine gets into the middle of the
"tube" and in that environment appears blue or purple.  Amylopectin (the
branched form of starch) can be purple or red with iodine stain.

You can see an beautiful example of this in a paper by Kakefuda and Duke
(Plant Physiology 75: 278-280, 1984) in which they ran various starch
hydrolases on a nondenaturing polyacrylamide gel, then electrophoretically
transferred the enzymes through a second polyacrylamide gel containing
starch (like a western transfer).  The enzymes partially chew "holes" in
the starch as they go and after staining the second gel with iodine the
holes appear blue, brown, grey or red.  It is a very nice technique but one
must wear a mask or not talk when setting it up because salivary amylases
can speckle the second gel with white spots!

Jon

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