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Structure:Structure:

Isocitrate dehydrogenase is SCOP classified as an alpha beta structure. Its secondary composition consists of mainly alpha helices and beta sheets which are arranged into three layer alpha beta alpha sandwich structures. The entire protein consists of two side by side sandwich structures that face opposite directions. This then causes the proteins two active sites to face opposite directions as well. These two groups make up the A and B subunits of isocitrate dehydrogenase.

Human Isocitrate Dehydrogenase bound by NADH and CA2+ and Citrate Image made using JMOL

Citric Acid is converted to alpha-ketoglutarate

Image from: http://en.wikipedia.org/wiki/Isocitrate_dehydrogenase

Function:Function:

Isocitrate dehydrogenase is a digestive enzyme that is used in the citric acid cycle. Its main function is to catalyze the oxidative decarboxylation of isocitrate into alpha-ketoglutarate. Human isocitrate dehydrogenase is regulation is not fully understood however, it is known that NADP and Ca2+ bind in the active site to create three different conformations. These conformations form in the active site and are as follows: a loop is form in the inactive enzyme, a partially unraveled alpha helix in the semi open form, and a alpha helix in the active form (PDB). Bacterial isocitrate dehydrogenase uses phosphorylation for regulation. The Ser94 residue undergoes reversible phosphorylation causing structural changes in the active site which hinders the catalytic function of the enzyme (PBD).

Image from:http://en.wikipedia.org/wiki/Isocitrate_dehydrogenase

Active site of A chain. Human isocitrate dehydrogenase Image made using JMOL

Ecol i E coli isocitrate dehydrogenase after regulation by phosporylation of Ser94 Image made using JMOL