Lactic acid
Lactic acid is a chemical compound that plays a role in several biochemical processes. It is the acid that gives old milk its sour taste, and it accumulates in skeletal muscles after extensive exercise, causing muscle pain.
It is a carboxylic acid and an alcohol; its chemical formula is C3H6O3 and its structure is
H OH O
\ | //
H - C - C - C
/ | \
H H OH
which is reflected in its systematic name 2-Hydroxypropanoic acid.
In solution, it can lose a proton from the COOH carboxy group, turning into the lactate ion CH3CHOHCOO-.
There are two optical isomers of lactic acid (and of lactate) since the central carbon atom is bound to four different groups. The first isomer is known as L(+)-lactic acid or (S)-lactic acid and the second is D(-)-lactic acid or (R)-lactic acid.
During one form of anerobic glycolysis or fermentation, L-lactate is produced from pyruvate via the enzyme lactate dehydrogenase[?]. This conversion also oxydizes one molecude of NADH[?] to NAD+, and this is the reason for the conversion: NAD+ has to be regenerated so that glycolysis can continue.
This lactic acid fermentation is performed by lactic acid bacteria[?] which are responsible for the sour taste of old milk and which are used in the production of dairy products such as cheese and yoghurt.
Lactic acid fermentation also occurs in red blood cells, and in skeletal muscle during intense exertion when sufficient amounts of oxygen cannot be supplied fast enough. This lactate is released into the bloodstream. The typical lactate concentration in the blood is 1-2 mM/L. The liver takes up about 60% of the lactate and reoxydizes it to pyruvate, which is then reconverted to glucose in a process known as gluconeogenesis. The glucose enters the bloodstream and can be used by the tissues. This glucose → lactate → glucose cycle, originally described by Carl and Gerti Cori, is known as the Cori cycle. About 40% of the lactate is taken up by well oxygenated muscle cells and oxydized to pyruvate, which is then directly used to fuel the citric acid cycle.
The CAS number of lactic acid is 50-21-5. To distinguish between the optical isomers, one can use CAS 79-33-4 for L-lactic acid and CAS 10326-41-7 for D-lactic acid and CAS 598-82-3 for an optically inactive mixture of the two.
Lactic acid is the result of malolactic fermentation[?], a process used in winemaking to convert sharp-tasting malic acid into the gentler lactic.
So, among other things, this "Small Print!" statement
you may.html">may.html">may distribute copies of this etext if you want to.
*BEFORE!* YOU USE OR READ THIS ETEXT
etext, you indicate that you understand, agree to and accept
a refund of the money (if any) you paid for this etext by
you got it from. If you received this etext on a physical.html">physical
This PROJECT GUTENBERG-tm/tm.html">tm/tm.html">tm etext, like most PROJECT GUTENBERG-tm etexts,
through the Project Gutenberg Association (the "Project").
on or for this work, so the Project (and you!) can copy and
without paying copyright.html">copyright royalties. Special rules, set forth
under the "PROJECT GUTENBERG" trademark.html">trademark.
Please do not use the "PROJECT GUTENBERG" trademark to market
efforts to identify, transcribe and proofread public domain
medium they may be on may contain "Defects". Among other
corrupt data, transcription errors, a copyright or other
disk or other etext medium, a computer.html">computer virus, or computer
But for the "Right of Replacement or Refund" described below,
receive this etext from as a PROJECT GUTENBERG-tm etext) disclaims
legal fees, and [2] YOU HAVE NO REMEDIES FOR NEGLIGENCE OR
INCLUDING BUT NOT LIMITED TO INDIRECT, CONSEQUENTIAL, PUNITIVE
POSSIBILITY OF SUCH DAMAGES.
If you discover a Defect in this etext within 90 days of
you paid for it by sending an explanatory note.html">note within that
on a physical medium, you must return it with your note, and
copy. If you received it electronically, such person.
On
wordlookup.net
All is still licensed under the GNU FDL.
It uses material from the wikipedia.
|
|