Ascorbic Acid

Ascorbic acid is a naturally occurring <a href="http://en.wikipedia.org/wiki/Organic_compound" title="Organic compound" >organic compound</a> with<a href="http://en.wikipedia.org/wiki/Antioxidant" title="Antioxidant" >antioxidant</a> properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. Ascorbic acid is one form ("<a href="http://en.wikipedia.org/wiki/Vitamer" title="Vitamer" >vitamer</a>") of <a href="http://en.wikipedia.org/wiki/Vitamin_C" title="Vitamin C" >vitamin C</a>. The name is derived from a- (meaning "no") and scorbutus (<a href="http://en.wikipedia.org/wiki/Scurvy" title="Scurvy" >scurvy</a>), the disease caused by a deficiency of vitamin C. Because it is derived from <a href="http://en.wikipedia.org/wiki/Glucose" title="Glucose" >glucose</a>, many animals are able to produce it, but humans require it as part of their nutrition. Other vertebrates lacking the ability to produce ascorbic acid include other primates, guinea pigs, teleost fishes, bats, and birds, all of which require it as a dietary micronutrient (that is, a vitamin).

See also: color retention agent

<h2 >Niche, non-food uses</h2>

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<li >Ascorbic acid is easily oxidized and so is used as a reductant in photographic developer solutions (among others) and as a <a href="http://en.wikipedia.org/wiki/Preservative" title="Preservative" >preservative</a>.</li>

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<li >In <a href="http://en.wikipedia.org/wiki/Fluorescence_microscope" title="Fluorescence microscope" >fluorescence microscopy</a> and related fluorescence-based techniques, ascorbic acid can be used as an<a href="http://en.wikipedia.org/wiki/Antioxidant" title="Antioxidant" >antioxidant</a> to increase fluorescent signal and chemically retard dye <a href="http://en.wikipedia.org/wiki/Photobleaching" title="Photobleaching" >photobleaching</a>.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-13" >[14]</a></li>

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<li >It is also commonly used to remove dissolved metal stains, such as iron, from fiberglass swimming pool surfaces.</li>

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<li >In plastic manufacturing, ascorbic acid can be used to assemble molecular chains more quickly and with less waste than traditional synthesis methods.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-14" >[15]</a></li>

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<li >Heroin users are known to use ascorbic acid to dissolve heroin in water, so that it can be injected.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-15" >[16]</a></li>

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Ascorbic acid is found in plants, animals, and single-cell organisms where it is produced from <a href="http://en.wikipedia.org/wiki/Glucose" title="Glucose" >glucose</a>.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-Stone-16" >[17]</a> All animals either make it, eat it, or else die from <a href="http://en.wikipedia.org/wiki/Scurvy" title="Scurvy" >scurvy</a> due to lack of it. Reptiles and older orders of birds make ascorbic acid in their kidneys. Recent orders of birds and most mammals make ascorbic acid in their liver where the enzyme <a href="http://en.wikipedia.org/wiki/L-gulonolactone_oxidase" title="L-gulonolactone oxidase" >L-gulonolactone oxidase</a> is required to convert glucose to ascorbic acid.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-Stone-16" >[17]</a>

Humans, some other primates, and guinea pigs are not able to make L-gulonolactone oxidase because of a genetic mutation and are therefore unable to make ascorbic acid.

Synthesis and signalling properties are still under investigation.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-valpuesta-17" >[18]</a>

Animal Biosynthesis Pathway of Ascorbic Acid</div>

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Animal Ascorbic Acid Biosynthesis Pathway The biosynthesis of Ascorbic Acid starts with the formation UDP-glucuronic acid. UDP-glucuronic acid is formed when UDP-glucose undergoes two oxidations and a hydrolysis catalyzed by the enzyme UDPglucose 6-dehydrogenase. UDPglucose 6-dehydrogenase uses the co-factor NAD+ as the electron acceptor. Then the transferase UDPglucuronate pyrophosphorylase is used to separate the sugar and the nucleoside diphosphate. Then glucuronokinase, with the cofactor ATP, leads to the product D-glucuronic acid. Afterwards the ring is opened by an oxidation at C-1 followed by hydrolysis. Then the aldehyde is reduced to a primary alcohol using the enzyme glucuronate reductase and the cofactor NADPH. This is followed by lactone formation with the hydrolase gluconolactonase between the carbonyl on C1 and hydroxyl group on the C4. L-gulonolactone then reacts with oxygen, which is catalyzed by the enzyme L-gulonolactone oxidase (humans and other primates do not have this enzyme) and the cofactor FAD+. This reaction produces 2-oxogulonolactone which spontaneously undergoes enolization to form ascorbic acid.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-West_Sussex_2009-18" >[19]</a>

Plant Ascorbic Acid Biosynthesis Pathway There are many different biosynthesis pathways for ascorbic acid in plants. Most of these pathways are derived from products found in glycolysis and other pathways. For example, one pathway goes through the plant cell wall polymers.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-19" >[20]</a>

The Plant Ascorbic Acid Biosynthesis Pathway most principal seems to be L-galactose. L-galactose reacts with the enzyme L-galactose dehydrogenase where the lactone ring opens and forms again but with between the carbonyl on C1 and hydroxyl group on the C4 resulting in L-galactonolactone.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-West_Sussex_2009-18" >[19]</a>

L-galactonolactone then reacts with the mitochondrial ﬂavoenzyme L-galactonolactone dehydrogenase<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-20" >[21]</a> to produce ascorbic acid.<a href="http://en.wikipedia.org/wiki/Ascorbic_acid#cite_note-West_Sussex_2009-18" >[19]</a> An interesting fact about L-ascorbic acid is that it has shown to have a negative feedback on L-galactose dehydrogenase in spinach.

Ascorbic Acid

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