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<blockquote data-quote="tareload" data-source="post: 228302"><p>[URL unfurl="true"]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4959991[/URL]</p><p></p><p></p><p></p><h3><strong>Vitamin C</strong></h3><p><strong>Biosynthesis, recycling and degradation in mammals</strong></p><p><strong></strong></p><p>[URL unfurl="true"]https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x[/URL]</p><p></p><p><em>Vitamin C (or l-ascorbic acid; hereafter, ‘ascorbic acid’ and ‘ascorbate’ will always refer to ‘l-ascorbic acid’ and ‘l-ascorbate’) is unique among vitamins for several reasons. It is present in various foods, particularly of plant origin, in quantities (typically 10–100 mg/100 g [[<a href="https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b1" target="_blank">1</a>]]) that are several orders of magnitude higher than those of other vitamins. This is certainly related to the facts that it is formed from sugars, which are abundant compounds, and that its biochemical synthesis is rather simple. Another unique aspect of ascorbic acid is that it is a vitamin for only a few vertebrate species, those which have lost the capacity to synthesize it. From a structural point of view, it is also one of the rare compounds containing a hydroxyl group that is so acidic as to be completely dissociated at neutral pH (carbon-3 hydroxyl pKa = 4.2). This is related to the fact that ascorbic acid comprises two conjugated double bonds and that a resonance form can be written for the deprotonated monoanionic form (<a href="https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#f1" target="_blank">Fig. 1</a>). Resonance forms can also be written for the form of vitamin C that has lost one electron (<a href="https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#f1" target="_blank">Fig. 1</a>), making the radical semidehydroascorbate (SDA) much more stable, and thus much less reactive, than most other free radicals [[<a href="https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b2" target="_blank">2</a>]]. Vitamin C is therefore able to play the role of a free-radical scavenger [[<a href="https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b3" target="_blank">3</a>]], reacting with highly ‘aggressive’ (oxidizing) species to replace them by a much less reactive and, moreover, enzymatically recyclable one, SDA. Ascorbate is certainly the most abundant water-soluble compound acting in one-electron reactions, and this is most probably why it plays the role of a cofactor in reactions catalyzed by a number of metal-dependent oxygenases. The Cu+-dependent monooxygenases peptidylglycine α-amidating monooxygenase and dopamine β-hydroxylase convert two ascorbate molecules to two SDAs per catalytic cycle [[<a href="https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b4" target="_blank">4</a>]]. In the case of Fe2+/α-ketoglutarate-dependent dioxygenases (e.g. collagen prolyl and lysyl hydroxylases, the two hydroxylases involved in carnitine biosynthesis [[<a href="https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b5" target="_blank">5</a>]], the asparaginyl hydroxylase that modifies hypoxia-inducible factor 1 (HIF-1) [[<a href="https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b6" target="_blank">6</a>]]), ascorbate most probably serves to reconvert inactive, Fe3+-containing enzyme (which results from abortive catalytic cycles) to the active, Fe2+-containing form [[<a href="https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b5" target="_blank">5</a>]]. Because of these important roles, it is not surprising that vitamin C deficiency leads to a debilitating disorder, scurvy, in man and in animals unable to synthesize the vitamin.</em></p><p></p><p></p><p></p><p></p><p>[ATTACH=full]23666[/ATTACH]</p><p></p><p></p><p>[ATTACH=full]23667[/ATTACH]</p></blockquote><p></p>
[QUOTE="tareload, post: 228302"] [URL unfurl="true"]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4959991[/URL] [HEADING=2][B]Vitamin C[/B][/HEADING] [B]Biosynthesis, recycling and degradation in mammals [/B] [URL unfurl="true"]https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x[/URL] [I]Vitamin C (or l-ascorbic acid; hereafter, ‘ascorbic acid’ and ‘ascorbate’ will always refer to ‘l-ascorbic acid’ and ‘l-ascorbate’) is unique among vitamins for several reasons. It is present in various foods, particularly of plant origin, in quantities (typically 10–100 mg/100 g [[[URL='https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b1']1[/URL]]]) that are several orders of magnitude higher than those of other vitamins. This is certainly related to the facts that it is formed from sugars, which are abundant compounds, and that its biochemical synthesis is rather simple. Another unique aspect of ascorbic acid is that it is a vitamin for only a few vertebrate species, those which have lost the capacity to synthesize it. From a structural point of view, it is also one of the rare compounds containing a hydroxyl group that is so acidic as to be completely dissociated at neutral pH (carbon-3 hydroxyl pKa = 4.2). This is related to the fact that ascorbic acid comprises two conjugated double bonds and that a resonance form can be written for the deprotonated monoanionic form ([URL='https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#f1']Fig. 1[/URL]). Resonance forms can also be written for the form of vitamin C that has lost one electron ([URL='https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#f1']Fig. 1[/URL]), making the radical semidehydroascorbate (SDA) much more stable, and thus much less reactive, than most other free radicals [[[URL='https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b2']2[/URL]]]. Vitamin C is therefore able to play the role of a free-radical scavenger [[[URL='https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b3']3[/URL]]], reacting with highly ‘aggressive’ (oxidizing) species to replace them by a much less reactive and, moreover, enzymatically recyclable one, SDA. Ascorbate is certainly the most abundant water-soluble compound acting in one-electron reactions, and this is most probably why it plays the role of a cofactor in reactions catalyzed by a number of metal-dependent oxygenases. The Cu+-dependent monooxygenases peptidylglycine α-amidating monooxygenase and dopamine β-hydroxylase convert two ascorbate molecules to two SDAs per catalytic cycle [[[URL='https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b4']4[/URL]]]. In the case of Fe2+/α-ketoglutarate-dependent dioxygenases (e.g. collagen prolyl and lysyl hydroxylases, the two hydroxylases involved in carnitine biosynthesis [[[URL='https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b5']5[/URL]]], the asparaginyl hydroxylase that modifies hypoxia-inducible factor 1 (HIF-1) [[[URL='https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b6']6[/URL]]]), ascorbate most probably serves to reconvert inactive, Fe3+-containing enzyme (which results from abortive catalytic cycles) to the active, Fe2+-containing form [[[URL='https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2006.05607.x#b5']5[/URL]]]. Because of these important roles, it is not surprising that vitamin C deficiency leads to a debilitating disorder, scurvy, in man and in animals unable to synthesize the vitamin.[/I] [ATTACH type="full" alt="1658154240771.png"]23666[/ATTACH] [ATTACH type="full" alt="1658154280832.png"]23667[/ATTACH] [/QUOTE]
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Testosterone Replacement, Low T, HCG, & Beyond
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TRT alleviating depression?
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