Amino acid catabolism: principal carbon product of arginine breakdown Catabolic processing of arginine in humans yields which key TCA-linked intermediate as its carbon skeleton end-product?

Introduction / Context:
Arginine is a urea cycle amino acid. Its catabolism intersects nitrogen disposal and carbon metabolism. Correctly identifying its carbon fate helps in understanding glucogenic versus ketogenic classifications.

Given Data / Assumptions:

• Human hepatic metabolism with functional urea cycle.
• We track carbon skeleton fate, not transient cycle by-products.

Concept / Approach:
Arginase hydrolyzes arginine to urea and ornithine. Ornithine converts to glutamate semialdehyde, then to glutamate, which undergoes oxidative deamination/transamination to yield alpha-ketoglutarate. Thus, arginine is glucogenic via alpha-ketoglutarate. Although fumarate appears within the urea cycle (from argininosuccinate cleavage), the principal carbon skeleton end-product after complete catabolism is alpha-ketoglutarate.

Step-by-Step Solution:
Arginine → ornithine + urea (arginase).Ornithine → glutamate semialdehyde → glutamate.Glutamate → alpha-ketoglutarate (via GDH or transamination).Therefore, the net carbon fate is alpha-ketoglutarate entering the TCA cycle.

Verification / Alternative check:
Biochemical charts classify arginine as glucogenic through conversion to alpha-ketoglutarate; clinical metabolism texts corroborate this route.

Why Other Options Are Wrong:
Fumarate is an intermediate generated in the urea cycle from argininosuccinate but not the final carbon skeleton product of arginine’s breakdown; oxaloacetate or succinate are not direct outcomes; acetoacetate would indicate a ketogenic route, which does not apply to arginine.

Common Pitfalls:
Equating transient urea cycle fumarate formation with the ultimate carbon skeleton product.

Final Answer:
Alpha-ketoglutarate.