Some Amino Acids Taken up by the Liver Are Used for Protein Synthesis

The liver is an important site of protein synthesis, and thus its priority position for amino acid uptake seems reasonable. Figure 32-7 shows that approximately 20% of the portal blood amino acid supply is used for protein synthesis in the liver, although this proportion varies with dietary protein intake. Almost all the serum proteins are synthesized in the liver, including such critical proteins as albumin and the blood­clotting factors. Although the liver-derived serum proteins serve many important functions, one function they do not serve is that of amino acid transport. The direct amino acid supply for protein synthesis in nonhepatic tissue comes from free amino acids in the blood, not from preformed serum proteins.