Vitamin C

Vitamin C atawa L-askorbat téh hiji zat gizi ésénsial pikeun primata luhur jeung sababaraha spésiés lianna. Askorbat perlu pikeun sababaraha rupa réaksi métabolismeu dina sakabéh awak sato jeung tutuwuhan sarta dihasilkeun ku awak ampir sakabéh organismeu, iwal manusa jeung sababaraha primata. Ieu vitamin kawentar ku balukar tina kakuranganana: barusuh (skorbut) .

Farmakofor vitamin C téh ion askorbatna. Pikeun mahluk hirup, askorbat téh antioksidan anu naméngan awak tina setrés oksidatif  sarta salaku kofaktor dina sababaraha réaksi énzimatik penting.

 Peran biologis 
Vitamin C téh L-énantiomér askorbat; énantiomér sabalikna, D-énantiomér, teu boga mangpaat fisiologis anu penting. Duanana mangrupa kiral pikeun wangun molekul anu sarua. Nalika ngaréduksi, L-askorbat nu réduktor kuat téh bakal robah jadi bentuk kaoksidasi, L-dehidroaskorbat . L-dehidroaskorbat lajeng bisa diréduksi balik jadi L-askorbat aktif ku énzim jeung glutation .

L-askorbat téh asam gula lemah anu wangunna patali jeung glukosa nu sacara alami diciptakeun ngahiji jeung ion hidrogén ngabentuk assam askorbat, atawa ngahiji jeung ion logam ngabentuk askorbat mineral.

 Mangpaat 
Pikeun manusa, vitamin C jétu pisan salaku antioksidan, ngurangan setrés oksidatif, salaku substrat peroksidaseu askorbat, ogé salaku kofaktor énzim dina biosintésis bahan-bahan biokimia penting. Vitamin C boga peran salaku donor éléktron pikeun dalapan énzimLevine M, Rumsey SC, Wang Y, Park JB, Daruwala R. Vitamin C. In Stipanuk MH (ed): "Biochemical and Physiological Aspects of Human Nutrition." Philadelphia: W B Saunders, kc. 541–567, 2000.:

 Tilu énzim dina hidroksilasi kolagénProckop DJ, Kivirikko KI: Collagens: molecular biology, diseases, and potentials for therapy. Annu Rev Biochem 64:403–434, 1995.Peterkofsky B: Ascorbate requirement for hydroxylation and secretion of procollagen: relationship to inhibition of collagen synthesis in scurvy. Am J Clin Nutr 54: 1135S–1140S, 1991.Kivirikko KI, Myllyla R: Post-translational processing of procollagens. Ann N Y Acad Sci 460: 187–201, 1985.. Ieu réaksi nambahkeun gugus hidroksil kana asam amino prolin atawa lisin dina molekul molekul (ngaliwatan hidroksilaseu prolil jeung hidroksilaseu lisil), antukna molekul kolagénna bisa ngabentuk wangun tripel héliks; ku kituna vitamin C jadi éséntial pikeun kamekarkeun jeung mulasara jaringan tatu, saluran getih, jeung kartilageMcGee, William, M.D., M.H.A., Assistant Professor of Medicine and Surgery, Tufts University School of Medicine; Medical Encyclopedia: Ascorbic acid.
 Dua énzim pikeun sintésis karnitinRebouche CJ: Ascorbic acid and carnitine biosynthesis. Am J Clin Nutr 54:1147S–1152S, 1991.Dunn WA, Rettura G, Seifter E, Englard S. Carnitine biosynthesis from gamma-butyrobetaine and from exogenous protein-bound 6-N-trimethyl-L-lysine by the perfused guinea pig liver. Effect of ascorbate deficiency on the in situ activity of gammabutyrobetaine hydroxylase. J Biol Chem 259:10764–10770, 1984.. Karnitin penting dina ngakut asam lemak ka mitokondria pikeun ngahasilkeun ATP.
 Anu tilu sésana nyaéta
 hidroksilaseu béta dopamin dina biosintésis norépinéfrin tina dopaminLevine M, Dhariwal KR, Washko P, Welch R, Wang YH, Cantilena CC, Yu R: Ascorbic acid and reaction kinetics in situ: a new approach to vitamin requirements. J Nutr Sci Vitaminol (Tokyo) Spec No:169–172, 1992.Kaufman S: Dopamine-beta-hydroxylase. J Psychiatr Res 11: 303–316, 1974..
 énzim nu nambahkeun gugus amida ka hormon péptida, antukna leuwih stabilEipper BA, Milgram SL, Husten EJ, Yun HY, Mains RE: Peptidylglycine alpha-amidating monooxygenase: a multifunctional protein with catalytic, processing, and routing domains. Protein Sci 2:489–497, 1993.Eipper BA, Stoffers DA, Mains RE: The biosynthesis of neuropeptides: peptide alpha-amidation. Annu Rev Neurosci 15:57–85, 1992..
 énzim nu ngamodulasi métabolismeu tirosinLindblad B, Lindstedt G, Lindstedt S: The mechanism of enzymic formation of homogentisate from p-hydroxyphenylpyruvate. J Am Chem Soc 92:7446–7449, 1970..

Jaringan biologis anu ngagundukkeun vitamin C leuwih ti 100 kali kadarna dina plasma getih nyaéta kelenjar adrénal, pituitari, timus, corpus luteum, jeung rétinaNew view at C Matthias A. Hediger , Nature Medicine  8, 445 - 446 (2002) 
doi:10.1038/nm0502-445 "Plasma vitamin C concentrations are maintained between 10 and 160 μM, and any excess of the vitamin is excreted by the kidney. In contrast, the vitamin is concentrated to at least 100 times the plasma level in specific tissues such as the adrenal glands, pituitary gland, thymus, retina, corpus luteum, and a variety of neuronal cell types.". Nu ngagundukkeun antara 10 n.k. 50 kalina nyaéta otak, limpa, bayah, téstis, kelenjar limfe, ati, tiroid, mukosa usus leutik, leukosit, pangkréas, ginjal, jeung kelenjar ciduh.

 Rujukan 
Vitamin C. Wikipédia basa Inggris (5 Dés. 2007).

 Bacaan salajengna 
Jurnal



Pustaka



 see Part IV, Chapter 7: Vitamin C  
  see Chapter 3: Vitamin C, The Champion Free Radical Scavenger 
 Monograph - Volumes I, II, III.

 Tumbu kaluar 
 AscorbateWeb — a collection of twentieth century medical & scientific literature on vitamin C in the tréatment and prevention of human diséase at séanet.com
 Healing Thresholds — Research on Vitamin C in the treatment of autism.  at héalingthresholds.com
  — "Prevention and treatment of occlusive cardiovascular disease with ascorbate and substances that inhibit the binding of lipoprotein (a)", Inventors: Matthias W. Rath and Linus C. Pauling
 vitamin C at United Kingdom Food Standards Agency

 Vitamin C Requirements: Optimal Health Benefits vs Overdose — a moderate dose advocacy site
 For Doctors: Preparation of Vitamin C IV's — by Andrew W. Saul, PhD. at doctoryourself.com
 Information regarding treatment of the Bird Flu with massive doses of ascorbate. — by Robert Cathcart, M.D. at orthomed.com

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