SUBJECT: TLC of digested starch

DATE: 4/97

 

An observation from studies in an introductory cell bio lab of

thin layer chromatography of "digested" starch and glycogen:

 

After supposedly complete digestion by alpha-amylase, and running

on TLC, three spots are stainable by acidified aniline-diphenylamine.

The top two spots we think are glucose and maltose, but are puzzled

about a third spot, between the origin and maltose. Supposedly alpha-

amylase digests starch and glycogen completely to glucose and maltose,

but not in our cell bio lab studies. Anyone have similar observations

and an explanation? I presume that it could be a tri-saccharide, but

why didn't the alpha amylase continue to cut off the maltose, leaving

a glucose molecule?

Jim Freed

Delaware, OH

 

 

Both starch and glycogen contain branches due to alpha-1,6 bonds between

glucose units. Alpha-amylase only breaks alpha-1,4 bonds which predominate

in starch and glycogen. Glycogen differs from starch in the frequency of

1-6 bonds - glycogen has more of them. I suspect the 3rd spot is a small

group of glucoses around a branch point. How big it is would depend on how

close the amylase could get to the branch point and that might depend on

the source of the amylase. If this is true, adding an enzyme that breaks

the alpha-1,6 bond such as alpha-glucosidase (they have broad substrate

specificity and would also eliminate the maltose), isomaltase (same

problem?) or "debranching enzyme" might eliminate the 3rd spot. If you try

this let me know how it works!

 

Jon

 

-----------------------------------------------------------------

Jonathan Monroe voice: 540-568-6649 (office)

Department of Biology 540-568-6045 (lab)

James Madison University fax: 540-568-3333

Harrisonburg, VA 22807-0001 e-mail: monroejd@jmu.edu

http://www.jmu.edu/biology/biofac/jmonroe/jmonroe.html

 

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