The Molecular weight of this is 90.09. Boiling point of lactic acid is 122°C and
melting point is 16.8°C. Its vapor pressure is 0.015mmHg at 25°C and heat of
vaporization is 54.0 kJ/mole. The density of lactic acid is 1.242g/cm3 at 20°C. Lactic
acid is an weak acid and its Ka value is 1.3 x 10-3 and pKa is 3.9 at 25°C (Ebbing, General
Chemistry A-15).
2. Biochemical roles
Lactic acid is exit as lactate (CH3CHOHCOO-) in aqueous situation, so in
biological condition it stays as lactate. Lactate is formed by muscle contracting and be
converted into glucose by liver (Figure 2).
Figure 2
The Cori-cycle. Lactate formed by active muscle is converted into glucose by the liver. This cycle shifts part of the metabolic burden of active muscle to the liver. [Lubert Stryer Biochemistry 4th ed: 577]
Lactate is normally formed from pyruvate in a variety of microorganisms. In
addition this reaction is occurs in ‘the cells of higher organisms when the amount of
oxygen is limiting’ as in muscle. ‘Lactate dehydrogenase’ catalyzes the reduction of
pyruvate by NADH to form lactate (Figure 3).
Figure 3
The conversion reaction of pyruvate to L-Lactate by NADH and Lactate dehydrogenase. [Lubert Stryer Biochemistry 4th ed: 497]
It happens in anaerobic condition because the regeneration of NAD+ in the reduction of
pyruvate to lactate sustained the continued operation of glycolysis under that condition.
Then the lactate moves to liver by blood stream. The lactate that enters the liver is
oxidized to pyruvate, a reaction favored by the low NADH/NAD+ ratio in the cytosol of
liver cells. After that pyruvate is converted into glucose by the gluconeogenic pathway
in liver.
3. Usage for Food
The fermentation of lactic acid is also made by bacteria (Campbell Biochemistry
487). This process makes sour taste of the old milk, so it is used to make fermented
vegetables like Kim-chi and pickles. This fermentation process is also used in the
products of dairy products like yogurt and cheese.
Works Cited
Darrell D. Ebbing, Steven D. Gammon. General Chemistry.8th ed, Boston:
Houghton Mifflin Company, 2005: A-15
Lubert Stryer. Biochemistry 4th ed, New York: W. H. Freeman and Company. 1995:
449-450, 497-498, 559
Mary K. Campbell. Biochemistry 3rd ed, Saunders College Publishing, 1998: 474, 487.
William H. Brown, Christopher S.Foote. Organic chemistry 3rd ed, Thomson learning,
Inc., 2002: 104
The Department of Chemistry of the University of Akron. The Chemical Database,
March 2005 <http://ull.chemistry.uakron.edu/erd/chemicals/1/95.html>
Enantiomers are nonsuperposable mirror images. The terms ‘chiral’ and ‘achiral’ refer to objects; the term enantiomers refers to the relationship between objects. [William H. Brown, Christopher S.Foote. Organic chemistry third ed; 104]
Web reference http://ull.chemistry.uakron.edu/erd/chemicals/1/95.html
LDH is an NADH-linked dehygrogenase and consists of four subunits. There are two kinds of sub units, designated M and H, which vary slightly in A.A. composition. [Mary K. Campbell Biochemistry 3rd ed: 474.
The major electron carriers in the oxidation of fuel molecules. [Lubert Stryer Biochemistry 4th ed: 449]
Gluconeogenesis is the process of synthesis of glucose from noncarbohydrate precursors. [Lubert Stryer Biochemistry 4th ed: 559]
