Kreb's Cycle Steps

Step 1

acetyl CoA + oxaloacetate → citrate

enzyme: citrate synthase

** release of CoA

Step 2

citrate → isocitrate

enzyme: aconitase (lyase)

Step 3

isocitrate → alpha-ketoglutarate

enzyme: isocitrate dehydrogenase

co-substrate: NAD⁺ → NADH

regulatory compounds:

• (+): ADP

• (-): ATP, NADH

** release of CO₂

Step 4

alpha-ketoglutarate → succinyl-CoA

enzyme: alpha-ketoglutarate dehydrogenase complex

co-substrate: NAD⁺ + CoA → NADH

regulatory compounds:

• (-): ATP, succinyl CoA, NADH

** release of CO₂

** creation of a thioester linkage to CoA

Step 5

succinyl-CoA → succinate

enzyme: succinyl CoA synthetase

co-substrate: ADP → ATP

** release of CoA

Step 6

succinate → fumarate

enzyme: succinate dehydrogenase

co-substrate: FAD → FADH₂

Step 7

fumarate → malate

enzyme: fumarase

co-substrate: H₂O

Step 8

malate → oxaloacetate

enzyme: malate dehydrogenase

co-substrate: NAD⁺ → NADH