The document discusses two shuttle systems that transport electrons from NADH in the cytoplasm into the mitochondria for ATP production: 1. The glycerol-3-phosphate shuttle produces 1.5 ATP per NADH transported by using glycerol-3-phosphate to carry electrons into the mitochondrial matrix. 2. The malate-aspartate shuttle produces 2.5 ATP per NADH transported by using malate and aspartate to carry electrons across the inner mitochondrial membrane. Both shuttles are required to regenerate NAD+ in the cytoplasm and transport reducing equivalents into the mitochondria for oxidative phosphorylation.

1. Net Yield of ATP from Glucose
• It depends on which shuttle is used!
• 30 ATP per glucose if glycerol-3-P
shuttle used
• 32 ATP per glucose if malate-asp
shuttle used
• In bacteria - no mitochondria - no extra
H+ used to export ATP to cytosol
10/3 = ~3ATP/NADH
6/3 = ~ 2ATP/FADH2
Prepared by Pratheep Sandrasaigaran

2. Shuttle Systems for e -
• Most of the NAD+ used in electron transport is
produced in the mitochondrial matrix.
• The binding site of Complex I for NADH is on the
matrix side of the inner membrane.
• The inner mitochondrial membrane is
impermeable to NAD+ and NADH.
Prepared by Pratheep Sandrasaigaran

3. Shuttle Systems for e -
• NADH formed in the cytosol of cells needs to
reoxidized into NAD+ to keep glycolysis going.
• Under anaerobic conditions, NAD+ is
regenerated by lactate dehydrogenase.
• Under aerobic conditions, the electrons of
NADH need to be shuttled into the matrix of the
mitochondria.
Prepared by Pratheep Sandrasaigaran

4. Shuttle Systems for e -
• "Shuttle systems" effect electron movement
without actually carrying NADH
• Glycerophosphate shuttle stores electrons
in glycerol-3-P, which transfers electrons to
FAD+
• Malate-aspartate shuttle uses malate to
carry electrons across the membrane
Prepared by Pratheep Sandrasaigaran

5. Glycerophosphate shuttle
Prepared by Pratheep Sandrasaigaran

6. Glycerophosphate shuttle
• This shuttle system uses two distinct glycerol 3-
phosphate dehydrogenases.
• The first is found in the cytoplasm, the other is found on
the intermembrane side of the inner mitochondrial
membrane.
Prepared by Pratheep Sandrasaigaran

7. Glycerophosphate shuttle
• In the first step, NADH produced in the cytosol transfers
its electrons to dihydroxyacetone phosphate to form
glycerol-3-phosphate.
• Glycerol-3-phosphate enters the intermitochondrial
space through a porin.
• Glycerol-3-phosphate is then reoxidized into
dihydroxyacetone phosphate by an FAD dependent
mitochondrial membrane glycerol 3-phosphate
dehydrogenase.
Prepared by Pratheep Sandrasaigaran

8. Glycerophosphate shuttle
• Electrons of NADH are transferred to FAD to form FADH2.
• The two electrons bound by the FADH2 are transferred
directly to coenzyme Q forming QH2.
• QH2 carries the electrons to complex III.
• The result of this shuttle is 1.5 ATP/NADH and this
shuttle is essentially irreversible
Prepared by Pratheep Sandrasaigaran

9. Glycerophosphate shuttle
Summary
Prepared by Pratheep Sandrasaigaran

10. Malate-aspartate shuttle
Prepared by Pratheep Sandrasaigaran

11. Malate-aspartate shuttle
• In the cytosol, oxaloacetate is reduced to malate by
malate dehydrogenase which uses NADH as the
reductant.
• Malate is transported across the inner
mitochondrial membrane by the dicarboxylic acid or
tricarboxylic acid carrier.
• Now in the matrix, the malate is reoxidized by
malate dehydrogenase to generate oxaloacetate
and NADH which can now transfer its electrons to
Complex I.
Prepared by Pratheep Sandrasaigaran

12. Malate-aspartate shuttle
• The oxaloacetate is transaminated by glutamine to
form aspartate and α-ketoglutarate.
• Aspartate can be transported across the inner
mitochondrial membrane by the dicarboxylic acid
carrier.
• In the cytosol aspartate transaminates α-
ketoglutarate to reform oxaloacetate completing
the cycle.
• This shuttle system generates 2.5 ATP/NADH and is
completely reversible.
Prepared by Pratheep Sandrasaigaran

13. Malate-aspartate shuttle
Summary
Prepared by Pratheep Sandrasaigaran