STEP 6: Oxidation of Succinate to fumarate-Succinate dehydrogenase, a flavo protein catalyzes conversion of succinate to fumarate with the production of FADH. One molecule of FADH is generated which will give 2 ATP molecule after oxidative phosphorylation.

STEP 7: Conversion of fumarate to malate-The dehydration of fumarate cauases release of water molecule and generation of malate. This reaction is catalyzed by fumarase, a streospecific enzyme which can be able to make distinction between trans and cis isomer of the molecule.

STEP 8: Oxidation of malate to oxaloacetate- This is the last step of kreb cycle where malate is oxidized to oxaloacetate by malate dehydrogenase. One molecule of NADH is generated which will give 3 ATP molecule after oxidative phosphorylation. Oxaloacetate again recombines with new molecule of acetyl coA to start another round kreb cycle.

Regulation of Kreb Cycle- There are 4 rate limiting steps in kreb cycle and the points where it can be regulated. These different steps are shown in Figure 6.2.
1.  Conversion of pyruvate into the acetyl CoA is the first step which allow the entry of sugar moiety into the kreb cycle. Pyruvate dehydrogenase complex is allosterically inhibited by high ratio of ATP/ADP, NADH/NAD⁺ and acetyl CoA/CoA.