Sandbox Reserved 338: Difference between revisions

===Mechanism===

   

In human metabolism, glycogen breakdown involves several enzymes, two of which are glycogen phosphorylase and glycogen-debranching enzyme <ref name="lehninger">Nelson, D. and Cox, M. Lehninger Principles of Biochemistry (5th Ed.), W.H. Freeman and Company, New York (2008).</ref>. Glycogen phosphorylase is responsible for the successive removal of glucose 1-phosphate molecules at the non reducing ends of glycogen branches <ref name="lehninger"/>. However, this enzyme’s activity ceases when it has reached a point four glucose residues away from an (alpha 1→6) branch point. Upon this, the GDE takes over and catalyzes the transfer of three branched glucose units to the nonreducing end of another branch to yield an (α1→4) linkage. The α-1,6-glycosidase activity of the GDE liberates the non-transferred glucose unit involved in a (α 1→6) bond <ref name="lehninger"/>.  

Although TreX is structurally different from the yeast and human GDE, it does however share functional similarities, and therefore a general human GDE mechanism is shown. In both species the  GDE catalyzes an intermolecular transfer  of glucose polymers from one 1,4-α-D-glucan branch to another 1,4-α-D-glucan branch nearby, In addition, both enzymes carry out the hydrolysis of an α-1,6-glycosidic linkage <ref name="isoamylaseglucanotransferase"> PMID: 17485831 </ref>. TreX does however show high specificity for side chains which are composed of 6 or more glucose residues <ref name="oligomer"> Park JT, Park HS, Kang HK, Hong JS, Cha H, Woo EJ, Kim JW, Kim MJ, Boos W, Lee S, Park KH (2008). "Oligomeric and functional properties of a debranching enzyme (TreX) from the archaeon Sulfobus solfataricus P2.". Biocatalysis and Biotransformation 26: 76–85.</ref>.

==Structure and Function==