Which statement correctly compares the malate–aspartate shuttle and the glycerol-3-phosphate shuttle in terms of energy yield per cytosolic NADH?

• A. Both shuttles yield the same ATP per NADH
• B. Malate-aspartate yields ~2.5 ATP per NADH; glycerol-3-phosphate yields ~1.5 ATP per NADH
• C. Malate-aspartate yields ~1.5 ATP per NADH; glycerol-3-phosphate yields ~2.5 ATP per NADH
• D. Malate-aspartate yields ~3.5 ATP per NADH; glycerol-3-phosphate yields ~2.5 ATP per NADH

Answer: (C)

Energy yield per cytosolic NADH depends on where the shuttle transfers electrons into the mitochondrial chain. The malate–aspartate shuttle effectively delivers electrons to mitochondrial NAD+, so each cytosolic NADH contributes about 2.5 ATP through oxidative phosphorylation. The glycerol-3-phosphate shuttle transfers electrons to FAD in the inner mitochondrial membrane, forming FADH2 that donates electrons further down the chain, which yields about 1.5 ATP per cytosolic NADH. So the statement that malate–aspartate gives around 2.5 ATP per NADH and glycerol-3-phosphate gives around 1.5 ATP per NADH is the correct comparison.