Proline is a nonessential amino acid, which means that it is manufactured from other amino acids in the liver (primarily from Ornithine, glutamine and glutamate), and does not have to be obtained from the diet. Proline and lysine (with the help of vitamin C) are converted to hydroxyproline and hydroxylysine, the two important components of collagen (the major protein of bones, cartilage, tendons, ligaments, skin, and muscle). Decreases in proline levels have been noted in prolonged endurance runners and others following prolonged exercise. Such individuals as well as those with pain in joints and muscles caused by insufficient or improper cartilage or collagen formation could benefit from extra proline in their diet. Proline supplementation may also benefit those recovering from traumatic injuries, including those of the skin (like severe burns). Proline is also thought to offset the effects of aging on skin by improving skin texture. Good sources are dairy products, eggs, beef and poultry.

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Collagens are among proteins that undergo several post-translational modifications, such as prolyl hydroxylation, that occur during elongation of the nascent chains in the endoplasmic reticulum………. The structure has a requirement for glycine, as every third residue, and is stabilized by the high content of proline and 4-hydroxyproline residues…….. Prolines are thus critical determinants of collagen structure and function.

 o      Krane, SM. (2008). The Importance of proline residues in the structure, stability and susceptibility to proteolytic degradation of collagens. Amino Acids, 35(4), 703-10.

The potential of proline to suppress reactive oxygen species (ROS) and apoptosis in mammalian cells was tested by manipulating intracellular proline levels exogenously and endogenously by overexpression of proline metabolic enzymes. Proline was observed to protect cells against H₂O₂, tert-butyl hydroperoxide and a carcinogenic oxidative stress inducer but was not effective against superoxide generators such as menadione…………These findings suggest that proline metabolism is more pivotal in maintaining redox homeostasis than previously thought with proline exhibiting dual functions as a pro-oxidant via PRODH (proline dehydrogenase) and as a ROS scavenger.

 o      Krishnan, N, Dickman, MB, & Becker, DF. (2008). Proline modulates the intracellular redox environment and protects mammalian cells against oxidative stress. Free Radic Biol Med, 44(4), 671-81.

The successful healing of wounds requires the local synthesis of significant amounts of collagen. The amino acid pool that is the immediate precursor for collagen synthesis within wounds has not been specifically identified but is likely to include the free amino acids contained in the extracellular wound fluid. This fluid is here shown to be rich in proline and its metabolic precursors: ornithine, glutamate, and glutamine……….. Experiments reported here tested the hypothesis that ornithine accumulating in the extracellular space of wounds serves as a precursor for proline contained in fibroblast secretory proteins…… the appearance of ornithine-derived free proline in the culture supernatants is quantitatively more important than its incorporation into protein and it is enhanced, rather than suppressed, by preformed proline. Therefore, ornithine may contribute to the synthesis of protein-bound proline in wounds by increasing the extracellular pool of free proline.

 o      Albina, JE, Abate, JE, & Mastrofrancesco, B. (1993). Role of ornithine as a proline precursor in healing wounds. J Surg Res, 55(1), 97-102.

1. The intracellular volume in granulation tissue was about 15% of the total urea space. 2. The experimental granuloma has a greater ability to retain amino acids during the proliferation phase than later during the synthesis of collagen. 3. The synthesis of collagen and other proteins by granulation tissue is related to the concentrations of proline and glutamic acid in the medium. 4. The rate of synthesis of proline from glutamic acid in granulation-tissue slices is greatest during collagen synthesis. It is enhanced by lactate. 5. Extracellular cations influence the synthesis of collagen and ouabain is inhibitory. Synthesis of other proteins is less sensitive in this respect. 6. It is suggested that the synthesis of collagen is related to the supply of certain amino acids, especially proline, and hence to the redox balance, and also to the function of the cell wall.

o      Aalto, M, Lampiaho, K, Pikkarainen, J, & Kulonen, E. (1973). Amino acid metabolism of experimental granulation tissue in vitro. Biochem J, 132(4), 663-71.

Methods for measurement of rates of collagen synthesis in vivo have thus far been technically difficult and often subject to quite large errors. In this paper a simplified method is described for obtaining synthesis rates of collagen and non-collagen proteins………. results suggest that the large dose of proline floods the precursor pools for protein synthesis, and that this effect can be maintained for quite long periods of time.

o      Laurent, GJ. (1982). Rates of collagen synthesis in lung, skin and muscle obtained in vivo by a simplified method using [3h]proline. Biochem J, 206(3), 535-44.

The aim of this study was to find a plasma biomarker, in relation with nitric oxide (NO), as a sign of brain damage severity following traumatic brain injury (TBI)……….. TBI induced a fall of plasma l-proline (Pro) concentrations. The time course of post-TBI neurological deficit showed also a decrease of neurological score…….. while a marked positive correlation has been found between the neurological score and the plasma level of Pro……….In conclusion, the plasma concentrations of Pro could be a promising marker of post-traumatic neurological deficit.

 o      Louin, G et al. (2007). Plasma concentrations of arginine and related amino acids following traumatic brain injury: proline as a promising biomarker of brain damage severity. Nitric Oxide, 17(2), 91-7.