Write a mechanism for the conversion of -ketoglutarate to succinyl CoA in step 4 of the citric acid cycle(Figure).

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O Acetyl CoA adds to oxaloacetate in an aldol H3C SCOA Acetyl CoA reaction to give citrate. HSCOA HO co, .co co2 Oxaloacetate Citrate O Citrate is isomerized by dehydration and rehydration to give isocitrate. NADHUH O Oxidation of (St-malate gives oxaloacetate, comploting the O NAD cycie. н сот но "O,C. co, Co H OH (S)-Malate (L-malate) Isocitrate O Fumarate undergoes conjugate addition of water to its double bond to give NAD+ O lsocitrate undorgoes oxidation and decarboxylation to give a-kotoglutarato. NADHH H20 (S-malate. + Co2 H. co, co, a-Ketoglutarate Fumarate HSCOA Oa-Ketoglutarate is decar- boxylated, oxidized, and converted into the thioester + NAD O Succinate is dehydro genated by FAD to give fumarate. FADH2 NADHH + Co, FAD succinyl CoA. CO HSCOA .co, COAS. Succinate GTP GDP Succinyl CoA 6 Succinyl CoA is converted to succinate in a reaction coupled to the phosphorylation of GDP to give GTP.