<P> In solution, it can ionize a proton from the carboxyl group, producing the lactate ion CH CH (OH) CO . Compared to acetic acid, its pK is 1 unit less, meaning lactic acid deprotonates ten times more easily than acetic acid does . This higher acidity is the consequence of the intramolecular hydrogen bonding between the α - hydroxyl and the carboxylate group . </P> <P> Lactic acid is chiral, consisting of 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 . A mixture of the two in equal amounts is called DL - lactic acid, or racemic lactic acid . </P> <P> Lactic acid is hygroscopic . DL - lactic acid is miscible with water and with ethanol above its melting point which is around 17 or 18 ° C. D - lactic acid and L - lactic acid have a higher melting point . </P> <P> 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 and as high as 25 mmol / L afterward . </P>

When does lactic acid form in the body