Amino Acids, Peptides, and Proteins

Abstract

The ingestion of amino acids, peptides, and proteins from a variety of food sources is essential for maintaining health. Humans, as do other animals, use protein chiefly for its amino acid content. Proteins are converted to large and small peptides and individual amino acids by gastric and duodenal proteases (Castro 1991). Large peptides are hydrolyzed to small peptides, usually di- and tripeptides, by intestinal peptidases. Amino acids, dipeptides, and tripeptides leave the intestine and enter the hepatic portal system, but the peptides leave the liver and enter the peripheral blood as amino acids. The blood transports the amino acids to individual cells where they are placed in a cytosolic “pool.” They are utilized from the “pool” to synthesize proteins essential for growth and maintenance of healthy tissue. The continual hydrolysis and synthesis of proteins is central to their utilization. However, certain proteins and their hydrolytic products also carry out important functions unrelated to their primary metabolic mission.