Taurine
Taurine, or 2-aminoethanesulfonic acid, is an organic acid that is a major constituent of bile, and can be found in lower amounts in the tissues of many animals including humans.   Taurine is a derivative of the sulfur-containing (sulfhydryl) amino acid, cysteine. Taurine is the only known naturally occurring sulfonic acid.
Taurine is named after the Latin taurus, which means bull, as it was first isolated from ox bile in 1827 by Austrian scientists Friedrich Tiedemann and Leopold Gmelin. It is often called an amino acid, even in scientific literature, but as it lacks a carboxyl group it is not strictly an amino acid. It does contain a sulfonate group and may be called an amino sulfonic acid. Small polypeptides have been identified which contain taurine but to date no aminoacyl tRNA synthetase has been identified as specifically recognizing taurine and capable of incorporating it onto a tRNA. Also, contrary to popular belief, taurine is not synthesized from bull urine.

# Physiological roles
Taurine is conjugated via its amino terminal group with the bile acids chenodeoxycholic acid and cholic acid to form the bile salts sodium taurochenodeoxycholate and sodium taurocholate (see bile).
The low pKa (1.5) of taurine's sulfonic acid group ensures that this moiety is negatively charged in the pH ranges normally found in the intestinal tract and thus improves the surfactant properties of the cholic acid conjugate.
Taurine has also been implicated in a wide array of other physiological phenomena including inhibitory neurotransmission, long-term potentiation in the striatum/hippocampus, membrane stabilization, feedback inhibition of neutrophil/macrophage respiratory bursts, adipose tissue regulation, and calcium homeostasis.
Prematurely born infants who lack the enzymes needed to convert cystathionine to cysteine may become deficient in taurine. Thus, taurine is a dietary essential nutrient in these individuals and is often added to many infant formulas as a measure of prudence. There is also evidence that taurine in adult humans reduces blood pressure.
Recent studies show that taurine supplements taken by mice on a high-fat diet prevented them from becoming overweight. Studies have yet to be done on the effect of taurine on obesity in humans.  Currently taurine is being tested as an anti-manic treatment for bipolar depression. Recent studies have also shown that taurine can influence (and possibly reverse) defects in nerve blood flow, motor nerve conduction velocity, and nerve sensory thresholds in experimental diabetic neuropathic rats.  Taurine levels were found to be significantly lower in vegans than in a control group on a standard American diet. Plasma taurine was 78% of control values, and urinary taurine 29%.
In recent years, taurine has become a common ingredient in energy drinks. Taurine is often used in combination with bodybuilding supplements such as creatine and anabolic steroids, partly due to recent findings in mice that taurine alleviates muscle fatigue in strenuous workouts and raises exercise capacity. Taurine is also used in some contact lens solutions.
Taurine has also been shown in diabetic rats to decrease weight and decrease blood sugar.

# Taurine and cats
Taurine is essential for cat health, as a cat cannot synthesize the compound.  The absence of taurine causes a cat's retina to slowly degenerate, causing eye problems and (eventually) irreversible blindness. This condition is called central retinal degeneration (CRD).
In addition, taurine deficiency can cause feline dilated cardiomyopathy, and supplementation can reverse left ventricular systolic dysfunction.  However, the vegetarian lioness Little Tyke survived for years in captivity without imbibing the normal required dose of Taurine. (Pion et al 1988)  Taurine is now a requirement of the AAFCO and any dry or wet food product labeled approved by the AAFCO should have a minimum of 0.1% taurine.  For further AAFCO requirements for cats, consult the table here.

# Production
In 1993, approximately 5,0006,000 t of taurine (synthetic and natural) were produced; 50% for pet food manufacture, 50% in pharmaceutical applications. Synthetic taurine is obtained from isethionic acid (2-hydroxyethanesulfonic acid), which in turn is obtained from the reaction of ethylene oxide with aqueous sodium bisulfite.

# Safety data
Usage above 28.57 PPM in non-alcoholic beverages is deemed non-GRAS as determined by Flavor and Extract Manufacturers Association (FEMA) Expert Panel.  A typical energy drink that contains one gram of taurine corresponds to a concentration of about 4.083 ppm.

# Energy drinks
Taurine is an ingredient in many energy drinks and energy products. It is present in the alcoholic drinks Sparks, Spykes, VK blue, and Mobius Infused Lager. It is also contained in the energy drinks Monster (which contains 2000 mg, 1000 per serving), Von Dutch, Red Bull (1000 mg), SoBe Adrenaline Rush (960 mg), NOS (2750 mg), Boo Koo Energy (3000 mg), RedRave (1000 mg), XL, Full Throttle energy drinks (which contains 1194 mg. for a 16 oz. serving, 605 mg. for 8 oz.), and V (500 mg). The Rockstar energy drink, distributed by the Coca-Cola Corp., can contain up to 2000 mg of taurine, depending on the flavor, while Pepsi's SoBe Power Fruit Punch contains 50mg, and SoBe Energy (and its Lean variant) contain 16.5 mg per bottle. It is also in Foosh Energy Mints and Buzz Bites Chocolate Energy Chews, and is one of the main ingredients in the Indonesian energy powder Extra Joss. Both Hogan Energy Drink and WWE RAW Attitude Energy Drink Powered by Socko have 2000 mg per can (1000 mg per serving). Power C Vitamin Water, from Glaceau's line of vitaminwater, contains 25 mg, and their vitaminenergy contains 2000 mg of taurine per can.  Wired Energy Drinks X5000 contains 4400 mg of taurine in a 23.5 oz. can. AMP energy drink however, contains a relatively low 10 taurine mg per serving.
Despite its presence in many energy drinks, taurine has not been shown to be energy-giving, however the results of the studies into taurine usage have shown that taurine might help to reduce muscle fatigue.