The liver is an important site of protein metabolism. Which of the following statement(s) is/are true concerning protein metabolism by the liver?

b. Under certain conditions the amine group is removed from the amino acids in the liver and the carbon chain used for carbohydrate, lipid, or nonessential amino acid synthesis

d. Proteins synthesized by the liver include albumin, transferrin, fibrinogen, and apolipoproteins

Essentially all of the end products of dietary protein digestion are amino acids, which are absorbed by the enterocytes into the portal circulation in ionized states. Amino acids are taken up by hepatocytes by one of several active transport mechanisms. Amino acids are not stored in the liver but are rapidly used in the production of plasma proteins, purines, heme proteins, and hormones. Under certain conditions, the amine group is removed from the amino acids, and the carbon chain is used for carbohydrate, lipid, or nonessential amino acid synthesis. The ammonia formed as the result of deamination of amino acids is detoxified by one of two routes. The most important pathway involves conversion of ammonia to urea by enzymes of the Krebs-Henseleit cycle, found only in the liver. A second route of ammonia metabolism involves deamination of L-glutamine by the kidney, with excretion of ammonia into the urine. Essentially all albumin, fibrinogen, and apolipoproteins are derived from the liver which can add up to 50 grams of protein to the plasma per day. Of total hepatic protein synthesis, 75% is destined for export in plasma. Albumin, an important plasma protein synthesized in the liver, has a long half-life in plasma of about 19 days. This long half-life makes albumin an insensitive indicator of hepatic synthetic function.