The Krebs cycle uses NAD⁺ (nicotinamide adenine dinucleotide, oxidized form) as the substrate to make NADH.

Quick Scoop: Direct Answer

In the Krebs (citric acid) cycle, several dehydrogenase enzymes remove hydrogen/electrons from intermediates and reduce NAD⁺ to NADH.

Key points:

  • The molecule being “used up” to make NADH is NAD⁺ , which accepts electrons and a proton.
  • This happens at specific steps:
    1. Isocitrate → α‑ketoglutarate (via isocitrate dehydrogenase) uses NAD⁺ and produces NADH.
2. α‑Ketoglutarate → succinyl‑CoA (via α‑ketoglutarate dehydrogenase) uses NAD⁺ and produces NADH.

3. Malate → oxaloacetate (via malate dehydrogenase) uses NAD⁺ and produces NADH.

So in simple exam-style wording:

The Krebs cycle uses NAD⁺ as an electron acceptor (along with cycle intermediates like isocitrate, α‑ketoglutarate, and malate being oxidized) to make NADH.

Mini “story” version

You can picture each step as a tiny “redox handoff”: a carbon compound in the cycle loses high‑energy electrons, and NAD⁺ shows up like an empty battery, gets charged , and leaves as NADH to deliver that energy to the electron transport chain.

TL;DR: The Krebs cycle makes NADH by oxidizing intermediates and reducing NAD⁺ to NADH at three steps per turn of the cycle.

Information gathered from public forums or data available on the internet and portrayed here.