| The glycogen debranching enzyme is actually two enzymes
in one. It aids in the breakdown of glycogen. Glycogen is a polysaccharide
of glucose molecules and is the form humans (and other organisms) store
glucose in. Glycogen consists primarily of one to four carbon bonds between
glucose units and is branched about every ten units with a one to six carbon
bond between glucose units.
Glycogen phosphorylase, the enzyme primarily responsible for the breakdown of glycogen, is incapabale of severing the one to six bonds, and in fact stops severing the one to four bonds four glucose units before a branch point. Glycogen debranching enzyme is the enzyme responsible for removing the branches so that glycogen phosphorylase can continue it's work. Two reactions are required to remove a branch, hence the two enzymatic activities of the enzyme. The first activity, 4-alpha-D-glucanotransferase, transfers all but one of the glucose units on the branch to the main chain. The second activity, amylo-alpha-1,6-glucodiase, actually severs the one to six bond, releasing a free unit of glucose. A diagram of the enzyme's effects on glycogen is shown below.  |
