Lactic acid

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Lactic acid
Image:Lactic-acid-skeletal.png
Chemical name 2-hydroxypropanoic acid
Chemical formula C3H6O3
Molecular mass 90.08 g/mol
CAS number [50-21-5]
L: [79-33-4]
D: [10326-41-7]
D/L: [598-82-3]
Melting point L: 53 °C
D: 53 °C
D/L: 16.8 °C
Boiling point 122 °C @ 12 mmHg
SMILES CC(O)C(=O)O
Disclaimer and references

Lactic acid (IUPAC systematic name: 2-hydroxypropanoic acid), also known as milk acid, is a chemical compound that plays a role in several biochemical processes. Lactic acid is a carboxylic acid with a chemical formula of C3H6O3. It has a hydroxyl group adjacent to the carboxyl group, making it an alpha hydroxy acid (AHA). In solution, it can lose a proton from the acidic group, producing the lactate ion CH3CH(OH)COO.

Lactic acid is chiral and has two optical isomers. One is known as L-(+)-lactic acid or (S)-lactic acid and the other, its mirror image, is D-(-)-lactic acid or (R)-lactic acid. L-(+)-Lactic acid is the biologically important isomer.

In animals, L-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise. It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal which is governed by a number of factors including: monocarboxylate transporters, concentration and isoform of LDH and oxidative capacity of tissues. The concentration of blood lactate is usually 1-2 mmol/L at rest, but can rise to over 20 mmol/L during intense exertion.

Lactic acid fermentation is also performed by Lactobacillus bacteria. These bacteria can operate in the mouth; the acid they produce is responsible for the tooth decay known as caries.

In medicine, lactate is one of the main components of Ringer's lactate or lactated Ringer's solution. This intravenous fluid consists of sodium, chloride, potassium, and lactate in solution with distilled water in concentration so as to be isotonic compared to human blood. It is most commonly used for fluid resuscitation after blood loss due to trauma, surgery or a burn injury.

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[edit] Exercise and lactate

During intense exercise, such as sprinting type activities, when the rate of demand for energy is high, lactate is produced faster than the ability of the tissues to remove it and lactate concentration begins to rise. This is a beneficial process since the regeneration of NAD+ ensures that energy production is maintained and exercise can continue. The increased lactate produced can be removed in a number of ways including: oxidation to pyruvate by well-oxygenated muscle cells which is then directly used to fuel the citric acid cycle and conversion to glucose via the Cori cycle in the liver through the process of gluconeogenesis.

Contrary to popular belief, this increased concentration of lactate does not directly cause acidosis, nor is it responsible for delayed onset muscle soreness (muscle pain or "burning").<ref>Template:Cite journal</ref> This is because lactate itself is not capable of releasing a proton, and secondly, the acidic form of lactate, lactic acid, cannot be formed under normal circumstances in human tissues. Analysis of the glycolytic pathway in humans indicates that there are not enough hydrogen ions present in the glycolytic intermediates to produce lactic or any other acid.

The acidosis that is associated with increases in lactate concentration during heavy exercise arises from a separate reaction. When ATP is hydrolysed, a hydrogen ion is released. ATP-derived hydrogen ions are primarily responsible for the decrease in pH. During intense exercise, aerobic metabolism cannot produce ATP quickly enough to supply the demands of the muscle. As a result, glycolysis (anaerobic metabolism) becomes the dominant energy producing pathway as it can form ATP at high rates. Due to the large amounts of ATP being produced and hydrolysed in a short period of time, the buffering systems of the tissues are overcome, causing pH to fall and creating a state of acidosis. This may be one factor, among many, that contributes to the acute muscular discomfort experienced shortly after intense exercise.[citations needed]

Although it is not firmly established, it is possible that lactate may contribute to an acidotic effect via the strong ion difference, however this has not been well investigated in exercise physiology research and so its contribution is still uncertain.[citation needed]

[edit] Lactic acid in food

Lactic acid is used in a variety of food stuffs (such as yogurt) to act as an acidity regulator. Although it can be fermented from lactose (milk sugar), most commercially used lactic acid is derived from bacteria such as Bacillus acidilacti, Lactobacillus delbueckii or L. bulgaricuswhey to ferment carbohydrates from sources such as cornstarch, potatoes or molasses. Thus, although it is commonly known as "milk acid", products claiming to be vegan do sometimes feature lactic acid as an ingredient.

[edit] Lactic acid as a polymer precursor

Two molecules of lactic acid can be dehydrated to lactide, a cyclic lactone. A variety of catalysts can polymerise lactide to either heterotactic or syndiotactic polylactide, which as biodegradable polyesters with valuable (inter alia) medical properties are currently attracting much attention.

[edit] References

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[edit] See also

[edit] External links

cs:Kyselina mléčná da:Mælkesyre de:Milchsäure el:Γαλακτικό οξύ es:Ácido láctico eo:Lakta acido fr:Acide lactique is:Mjólkursýra it:Acido lattico he:חומצה לקטית lb:Mëllechsaier nl:Melkzuur ja:乳酸 no:Melkesyre nn:Mjølkesyre pl:Kwas mlekowy pt:Ácido láctico ro:Acid lactic ru:Молочная кислота sk:Kyselina mliečna su:Asam laktat fi:Maitohappo sv:Mjölksyra tr:Laktik asit zh:乳酸

Lactic acid

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