Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid.
Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage.
Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn.
In addition to dietary sources, proline can be synthesized from glutamate/glutamine, arginine, and ornithine. It can also be synthesized within enterocytes from degradation of small peptides.
In addition to collagen formation, proline has many other physiologic functions including regulation of gene expression, mTOR activation (integrating nutrient and growth factor signaling in cells), cellular redox reactions, protein synthesis, hydroxyproline generation, arginine synthesis, and it is a scavenging antioxidant.
Proline
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