<prompt> Substrate level phosphorylation is seen in reaction catalyzed by which enzyme of citric acid cycle?Pyruvate kinaseSuccinate thiokinasePhosphoglycerate kinaseAll of the above  <response>: The reaction involves a substrate level phosphorylation whereby a high energy phosphate is generated from the energy trapped in the thioester bond of succinyl CoA. The enzyme is succinate thiokinase step 5, Fig.18.2. A molecule of GDP is phosphorylated to GTP and succinate is formed. The GTP can be conveed to ATP by reacting with an ADP molecule: GTP ADP - GDP ATPRef: DM Vasudevan, Page no: 218 