What percentage of amino acids extracted by the liver are used for protein synthesis and oxidation?

• A. 25%
• B. 72%
• C. 57%
• D. 90%

Answer: (C)

Amino acids arriving in the liver from the portal circulation are allocated to the liver’s own protein synthesis and to oxidation for energy. About 57% of the amino acids extracted by the liver are used for these processes, meaning just over half are diverted to hepatic protein production and to energy generation through oxidation. The remainder goes to other hepatic pathways (such as gluconeogenesis or nitrogen disposal via the urea cycle) or is released back into circulation. This 57% figure reflects the balance the liver strikes between building proteins and meeting its energy needs. The exact percentage can vary with fed versus fasting states, but 57% is the best estimate among the options.