1. Oxaloacetate (4C) reacts with the acetyl group (2C) on acetyl CoA, thereby forming citrate (6C) and releasing coenzyme A so it can join with another acetyl group.
2. Citrate is converted to its isomer, isocitrate (6C), to prepare this substrate for the decarboxylation and redox reaction of the next step.
3. Isocitrate is acted upon by an enzyme complex including NAD+ or NADP (depending on the organism) in a reaction that generates NADH or NADPH, splits off a carbon dioxide, and leaves æ-ketoglutarate (5C).