Succinate dehydrogenase (SDH) is unique among TCA cycle enzymes because it:

• A Is the only TCA enzyme located in the mitochondrial matrix
• B Generates GTP directly and is the only energy-coupling step in the TCA cycle
• C Uses FAD as cofactor but releases it as FADH2 into the mitochondrial matrix
• D Is embedded in the inner mitochondrial membrane and is identical to ETC Complex II, directly transferring electrons to ubiquinone without generating NADH ✓

Explanation

SDH (succinate → fumarate) is the only TCA cycle enzyme that is an integral inner mitochondrial membrane protein; it is identical to Complex II of the ETC, oxidising succinate and passing electrons via FADH2 directly to CoQ (ubiquinone) without generating free FADH2 in the matrix. This yields only ~1.5 ATP per succinate (vs. 2.5 for NADH). GTP is generated by succinyl-CoA synthetase (a different TCA enzyme). All other TCA enzymes are matrix-soluble.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

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