Taurine - What is it, and what (physiologically) does it do?
This is a layman's review of taurine. If I make a mistake, I trust that the careful reader will call my attention to it (them) so that they may be corrected.
An understanding of taurine's many roles in preserving and enhancing human life continues to unfold. What is desired is a simple, straightforward cause and effect relationship between a chemical and the organism (man). Instead, the chemistry of taurine continues to baffle the investigator. Taurine wears too many hats; it is involved in too many, what appears to be, unrelated biological phenomena.
>From a simple beginning where the chemical, taurine, was found to be a necessary constituent of the digestive fluids (bile) of mammals, it was discovered to be present in of all things, shell fish. Perplexing, Science demands simple answers.
Then with the advent of technology, the amino acid analyzer, taurine shows up as the amino acid in highest concentration in the blood. Why?
Cat fanciers and others found that switching to lower cost diets for their animals led to spontaneous abortion, malformed fetuses; underweight, slow-growing offspring and blindness. Suddenly, taurine became an essential amino acid and if supplied in the diet as the chemical, or in meats corrects the problem.
Looking further, human milk is very high in taurine, unlike cow's milk. And certainly milk replacers intended for children is unsuited for them unless supplemented with taurine.
Then, taurine is discovered to help maintain cell membranes, thus permitting recovery from various environmental stresses. A myriad of problems such as effect the heart, lung, liver, brain, eye &c., seem to in some way involve low levels of taurine, or perhaps respond to taurine supplementation, but probably by different mechanisms. There is even a suggestion that frost-bite damage may be diminished by taurine.
Decreasing the toxicity of certain drugs and chemicals seems to be a potential benefit from this unusual amino acid.
Perhaps there is a simple answer to these very different apparent roles for taurine. I doubt it. Nature is the grand improviser and ultimate recycler. Having a limited number of starting materials, she has used them in wondrous ways.
Should one supplement the diet with taurine? You do it every day that you have a hamburger, fish and chips, even yogurt. The digestion of proteins in the diet yields up the amino acid, cysteine which through the miracle of enzyme chemistry converts cysteine to taurine. Do you need more, probably not unless you are an infant not suckling at mom's breast. (Conversion is inefficient in the early years.)
Chemistry of Taurine
Don't worry about the structure, we'll have more about this later. The structural formulas are not provided due to limitations of the system.
Taurine is an end product of metabolism (That means when you eat it, the body converts it to something else). Taurine is formed from cysteine (an amino acid). Cysteine is present in all proteins, so when you eat plenty of meat or other good sources of protein you supply your body with cysteine, and thus a supply of taurine.
The letters are short hand for the chemical elements that make up the compounds. The symbol ( - ) represents a bond (link) between adjacent elements. In some cases it is difficult to show these bonds so a space may be left instead. As example, between the H above and below the C in the cysteine structure. Bonds are the glue that hold the elements together.
H is the chemical symbol for hydrogen, S is for sulfur, C for carbon, O for oxygen and N for nitrogen. The -SH (or HS-) is called a sulfhydryl group. The -(NH2) is called an amino group. The -COOH is called a carboxyl group (since the compound is a carboxylic acid). The -SO3H is called a sulfonate group (as in sulfonic acid, -HSO3 ) The carbons connected by a ( - ) are said to be in a chain and thus cysteine has a 3 carbon chain. When an amino group (NH2) occurs in a molecule with a carboxyl group the compound may be called an amino acid.
How do you get from cysteine to taurine?
When the free (not in protein) amino acid cysteine is metabolized, it is first oxidized to a compound called cysteinesulfenic acid (the H on the S is replaced with an OH group). Then further oxidized to cysteinsulfinic acid (more oxygen is added to the sulfur) and finally yet more oxygen is added to yield cysteic acid (the sulfonate group is fully formed). This process yields energy when the SH group on the carbon chain is oxidized to a sulfonate.
And then the sulfonate is decarboxylated to form taurine. Decarboxylation (or decarboxylated, past tense) means the group - COOH is removed by some chemical process, in this case it's an enzymatic chopping off and discarding of the group to form carbon dioxide (CO2) in water (it's the fizz in soft drinks). Some references indicate that hypotaurine is a precursor to taurine. This simply means that before the process of complete oxidation of the sulfur occurs, decarboxyation takes place. I leave it to the authorities in this area to speak to the issue of whether cysteic acid or hypotaurine is the precursor to taurine.
This results is taurine which is also called an amino acid. This is stretching the terminology a bit. Most amino acids are, as we are discussing, alpha amino carboxylic acids. That is, they have an amino group (NH2) group attached to the first carbon following the fully oxidized carbon, i.e., the -COOH group. Sound confusiing, go to Amino Acids for a discussion of amino acids.
The reason for calling taurine an amino acid is based on the fact that the sulfur group ( -SO3H) has acid properties. That means that the hydrogen can be removed (donated to some other compound) and thus the molecule becomes; - SO3 - C - C - (NH2). Sinnce in chemistry a hydrogen donor is called an acid, taurine is called an acid, an amino acid. It's a bit of a stretch to call taurine an amino acid but that's what the text books do.
Let's say a little more about cysteine. Cysteine has three carbons. Imagine a straight line of C-C-C (actually the angle between the adjacent carbons is 60 degrees, not the 180 degrees of a straight line, but it's hard to represent on a keyboard.) Now let's number the carbons 3, 2, 1. O.K., now the number one carbon is fully oxidized, so the structure is more like this; C-C-COOH. Another way of numbering the carbons would be; beta, alpha, -, with the( - ) representing the first carbon.
It's time to add the sulfur (call it a sulfhydryl if you like). The sulfur is reduced, that is it has an hydrogen atom attached, so it's -SH. This goes on carbon 3 or the beta carbon if you prefer. We can represent it thusly;
Now you may have noted that the sulfhydryl group is shown as HS -. Again no big deal. Just an attempt to make the structure easy to represent. What we have left out are the hydrogen atoms that are on carbons 3, and 2 ( beta, alpha - remember).
It really isn't necessary to put them on the structure for most representative purposes but if we did, it would look something like this;
Another way of drawing cysteine would be as follows:
In this case, R is used to represent the side chain, "HS- C - ." In fact, other amino acids differ from cysteine just because of this side chain. See: Amino Acids for a discussion of amino acids.
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Let's review: Taurine is called an amino acid. It has a two carbon backbone with a sulfonate group on one end and an amino group on the other. Taurine is a metabolic end product of the amino acid cysteine, but not the only one.
H H
Here again is the chemical abbreviation (structure: HSO3- C - C - H
H (NH2)
Since we are interested in taurine our discussion of cysteine stops here.
Physiologically Activity of Amino Acids
Nature invented recycling. (At least Al Gore didn't make this claim.) In the case of cysteine, the end results could have been other than taurine. A protein (the building blocks of which are amino acids) when catabolized (broken down) yields(see amino acids and these amino acids can be further broken down into constituent parts. The carbon is oxidized to carbon dioxide, excess amino groups (NH2) are excreted in urine as urea and overall energy is obtained in the processes. Amino acids (and thus protein) have about the same energy values as carbohydrates (sugars and starches), which helps explain how carnivores (meat eaters) survive.
In the evolutionary process, nature had to make do with what was available. This is why there are so many alternative uses for most of the starting biochemicals. The following is a short list of how amino acids are used in processes quite apart from protein structures:
Some of Natures Alternative Uses for Amino Acids:
histidine - histamine (chemical messenger, antigen response)
tryptophan - niacin (an essential vitamin)
phenylalanine/tyrosine - thyroxine (a hormone
)
glutamic acid - GABA (chemical messenger, regulator of brain
activity)(GABA is gamma amino butyric acid)
arginine - urea (waste product of nitrogen metabolism
glycine/cysteine/glutamic acid - called glutathione (detoxifies
acetaminophen, donor of SH group, (principle low molecular weight
thiol (sulfur-containing) compound in living cells.)(glutathione is
called a tripeptide)
methionine - the sulfhydryl group is involved in oxidation/reduction
reactions.
lysine - carnitine is necessary for the metabolism of long chain fatty
acids.
These are but a few of the some thirty naturally occurring amino acids. Others have alternative roles as well, however, the above are the most physiologically important. And, the roles summarized above are only a few of the ways that nature has found to recycle amino acids.
Taurine has a number of physiological roles. Dr. Ryan Huxtable at the
University of Arizona who probably knows more about taurine than any of those
about, lists the major beneficial activities that taurine many be involved in
as:
An anticonvulsant (perhaps in epilepsy to control violent spasms)
Cardioprotecterant (when the heart is deprived of oxygen (called
ischemia),
taurine may help in the recovery process by maintaining the integrity of cell
membranes)
Membrane stabilizer (Not only in the heart but in other organs as well,
as
example in the eye in cone cells.)
As an anti-oxidant (much like vitamin E, taurine can react with free
radicals and prevent a chain reaction.)
A calcium modulator (taurine can bind to various metals including
calcium,
zinc and magnesium thus regulating the quantity of these metals that are free
within a cell)
Enantiostatic effect (really not sure what the Doctor means by this,
would
usually say that the compound provides a means of stabilizing the environment
within which it is active.)
Protective cellular functionality from the disruptive effects of
environmental stress (if you use an athlete as an example, when they are
active, the body's systems are affected in different ways. (See following
section)
Taurine's role in maintaining cellular environment
Probably the first evolving role for taurine in Nature was in the maintenance of a constant (homoeostatic) environment within the cell or tissues; something that would lead to water once inside the cell, being held there. Taurine still retains this role. It helps to maintain osmotic pressure.
Consider life in the ocean, the water is salty but along the coast line where life abounds, the water changes from fresh to brackish to the typical salt content of sea water. How do animals live in this changing environment? Using an oyster as an example, they must be able to adapt to survive. Taurine is the answer that Nature has provided. This compound can be bound to zinc or other metal ions and not have an effect on the osmotic pressure of the cells within the living organism. But when called on, taurine is freed, and the increase in free taurine maintains the balance between salt outside the cell and that within. If you are fond of oysters (or even if not), you may have noted sometimes the slight metallic taste (zinc is a metal), or smelled the slightly sulfur aura emitted by the oyster (complements of the sulfur component of taurine). If the oyster is "fat", you also may detect the slightly sweet flavor which is attributable to glycogen which is the storage compound for sugars for the oyster (in making a polymer of the sugars, Nature reduces the free content of the sugar within the cell and therefore modulates osmotic pressure). While oysters are used in this example, all shell fish have this same mechanism. The star fish is one that has been recognized as groups who study taurine as an emblem for their activities. (The Biology of Taurine, Proceedings of a symposium held October, 6-9, 1986).
Now how does life in the ocean by the lowly oyster, have anything to do with humans? (If you enter most any health food store, you now notice taurine as one of the ingredients im a large number of preparations.)
The shell fish lives in a non-expandable shell. (Granted it enlarges over time but the oyster is confined to a very rigid structure. So the living creature cannot expand, it must remain essentially the same size and shape throughout its life. Now compare that to our skull. Although it grows slowly, much like the oyster's shell increases in volume, it does so at a very slow rate. Cats also have this same limitation. Not so for the mouse and rat, their skull continues to grow in proportion to their bodies.
This only serves to demonstrate that we, humans, are different from other mammals that are often used as "experimental guinea pigs" to demonstrate the biological functions of our body's systems. And of course men and women, young and old, black and white, fat and thin, active and sedentary, &c., are different. Sometimes in only minor ways, other times in life threatening ways if treated in the same manner. (Much has been made of sickle cell anemia in some blacks as a demonstration project of emphasize how different, genetics can make one individual from another. Many other so called "diseases" could be cited.)
So nature set us (humans) apart from other animals. Unless we come to appreciate first the physiological difference between species and then other physiological differences within our species, little hope can be found for solving the myriad of afflictions that we may encounter due to what Nature designed.
While the cat is an imperfect organism to study to learn about humans, it does provide some cues. We now know that if the dam (mother cat) is deprived of taurine in her diet, her offspring will be malformed, often blind and many will die in infancy. Instead of taking this as a warning, that perhaps taurine serves a major role in development; nutritionist, doctors and specialist in the health professions continue to push diets that are not balanced. Offering up meal plans that are protein deficient, meat free, or vegetable based is the ultimate experiment conducted on our unborn and now growing children.
The results of this experiment will not be disclosed until after perhaps some twenty or so years. However, you need only look about to see that we in the so called developed countries of the world are producing children that are not as structurally sound as their parents or their grandparents. Look at the number of children now wearing glasses and contacts. The number far exceeds, even when you take into account active promotion by the lense industries, what should be expected. Take any other criterion you choose and draw your own conclusions.
Why, if there is so obvious a correlation between taurine consumption in the diet of mothers-to-be and in infants, has not the medical profession grasp upon this and offered up a solution. First, the medical profession has an amazing gap in their knowledge base. Look in any medical dictionary, text, journal and note the incomplete data base from which they can draw conclusions. Look at the courses offered in the colleges and universities, nutrition is very distant from courses on economics, office management, personal relationships, and even chemistry, biology and biochemistry. (Most biochemistry texts mention taurine only in passing as a metabolic end product of cysteine metabolism without suggesting any role that taurine may play in normal cell activity.)
The inventor of Gatorade recognized that brain levels of glucose drop to dangerously levels during intensive sporting activities. This coupled with decrease in blood volume causes participants to have fuzzy thinking, slow reflexes, poor coordination and muscle fatigue. Gatorade contains glucose and a balance of salts plus buffering compounds in a water solution. Players drinking Gatorade had improved muscular and mental skills and were superior over opponents that did not have benefit of the drink.
It has been demonstrated that when glucose is metabolized in the brain, glutarate is formed. This compound while a form of storage of carbon has other physiological functions as well. It is after all an acid (in fact dibasic). Not surprising buildup of this compound has far reaching consequences.
It is unknown whether adding taurine to the drink would have provided additional benefit. However, since these two compounds are involved in osmotic pressure control in the brain, it would be interesting to see the results of this do-able experiment.
Anyone that has grown New Guinea Impatiens recognizes the signs of water stress. The plant simply collapses, all the turgor goes from the stems and branches. However, within minutes of watering, the plant regains its beauty and goes on about its business of flowering. Or, driving alongside a corn field on a hot summer day, you can watch the leaves curl in an attempt to conserve moisture. Or, spend too much time in the water at the beach or the sauna and your skin wrinkles. All this is permissible for systems that don't depend upon conscious thought for species preservation.
There appears to be a developing role for taurine as a treatment for frost bite. Preventing ice crystal formation and disruption of cellular membranes is important for return of a frozen tissue to a normal state.
Nature has provided us with a mechanism for maintaining the aqueous environment of the cells of the brain (and also of the blood and the eyes) so that the whole organism continues to function.
Vision and taurine are somehow related.
As mentioned for the cat, you need only visit a pet food store and ask what is required for proper vision in the cat and you will be immediately informed that is taurine, the amino acid. How can it be that the veterinary industry has accepted this premise but it is not by the human health industry? Maybe because taurine isn't required for humans after some point in their development(?).
You may accept this argument but before you do, consider this; many people live to a ripe old age without the benefit or need for glasses. Others with the aid of glasses do very well into their old age. Unfortunately, there is a population that are not so lucky. Is it because they have abused their eyes? Not eaten enough carrots? Masturbated, this was once said to cause blindness? Or perhaps they just didn't choose their parents well enough, i.e., it's in their genes? The medical profession doesn't know. And neither do I. However, wouldn't you think that with the magnitude of this problem (from which some percentage of the scientific and medical professions cannot be immune) that there would be more intensive effort to study the effects of taurine on vision. Nope! So we await the research that will demonstrate that taurine must be administered by some pathway than through the diet, that cross-membrane transport may be important for uptake, the critical concentration within the eye ball itself that is important for visual acuity and/or that repair of the cones is possible. Maybe.
So what to do? It is unfortunate that people have to take risk with their own lives by subjecting themselves to self-medication. But that's what is happening. The so called "health" industry of homeopathic remedies and other treatments has exploded. Now, we have a second problem in addition to the first. (Remember, the mother who dosed the kids with unbalanced meals) Now we have adults that are consuming a wide range of "Natures" remedies. Where is the Food and Drug Administration when we need them.
Other Worries
Cholesterol brings with it a bad connotation, but it is absolutely essential for life. While not now considered as important enough to be taught in some biochemical courses. The bile salts are a necessary ingredient in the digestion process. They solublize material in the digesta and make it possible for the body to assimilate fats and proteins. The bile salts are chemical compounds made up of different bile "acids", cholic acid being the most prevalent. The salt is the result of reacting the acid with the amino group on taurine (or glycine). Is it possible that low levels of protein in the diet would interfere with absorption of other nutrients. (Vegetable lovers take note, the soybean's other name is glycine max, so not to worry(?).
Quinine (as used to treat malaria and in tonic water) has been suggested to have a damaging effect on vision. Perhaps as being an antagonist to taurine's beneficial effects. Bad news for the gin and tonic drinker(?)
In oxygen insufficiency to the heart muscle, taurine appears to be beneficial in maintaining the integrity of cell membranes. Retinae ischemia is the diminished blood supply to the retina due to failure of the arterial circulation; it may occur as a result of arterial embolism or spasm; poisoning, as by quinine; or exsanguination from recurring profuse hemorrhages(e.g., in parturition, gastric and duodenal ulcers, and pulmonary tuberculosis; bilateral transitory or permanent blindness may result. How to increase taurine concentration in the eye (?).
Macular degeneration - the macula is an area near the center of the retina where cones are located. Loss of macular cones due either to genetic or age or chemical insult results in loss of ability to see objects clearly. The area alongside the cones further from the center of vision is occupied predominately by rods. So peripheral vision may remain when there is macular degeneration.
Decline in visual acuity with age:
Age Diopters
8 13.8
16 12
24 10.2
32 8.2
40 5.8
48 2.5
56 1.25
64 1.1
72 (a)
80 (a)
88 (a)
(a) data not provided.
(b) from Stedman's Medical Dictionary.
Is there a correlation between taurine in the eye and declining vision?
This from: Brain Res. Brain Res. Reviews: 1991. By J. B. Lombardini. Taurine is present in high concentrations in the retina of all species tested, while the retinal concentrations of the enzymes necessary to synthesize taurine are presumed to vary among those species. The documented low activity of cysteinesulfinic acid decarboxylase, a key enzyme in taurine biosynthesis, in the livers of cat, monkey and human possibly reflect low activity in their retinas, indicating a reliance on the diet as an important source of taurine....
Entering the twenty first century
I leave you with this parting shot. In and about 1985 several "discoveries" came together to improve how we treat our new-borne.
In the case of the premature, the damaging effect of high oxygen content of the developing eye was finally recognized. In particular, incubator infants were in danger. Eyes of the infant are now protected from the oxygen enriched atmosphere of the incubator.
Soybean protein became available for making store-bought formulas in the 60's. In 1985, it took the skills of a Doctor in Memphis, Tennessee to recognize that all was not right with babies in his hospital. They were in a state of shock. He discovered that in isolating protein from the soybean, that the manufacturers were using an extraction process based on sodium hydroxide. The resulting sodium proteinate contained no chloride. When milk replacers were formulated, the product was deficient in the chloride ion. Since sodium and chloride must be in balance for proper cell function, some infants were affected. Manufacturers now balance the sodium and chloride content of their products and all is well with the world (?).
And while veterinarians came to realize that cats were particularly sensitive to the level of taurine in the diet, it was only after 1985, in recognition that human babies were also vulnerable to low levels of taurine that it became a issue. Now most major suppliers of milk replacers have taurine as an ingredient. (Human milk is very rich in taurine as opposed to cow milk, and plants contain very little.)
Interest in taurine has shifted from the nutritional aspects of the physiological effects on human body systems, much remains to be learned on the role of this most important amino acid on the aged. It is hoped that renewed interest in this subject will lead to further discoveries and benefit to us all. At the very least, biochem textbooks should put taurine back in the subject matter covered so that tomorrow's scientist will recognize the importance of this biochemical.
The final question.
Do I recommend taking taurine as a dietary supplement. No, I believe that a well balanced diet containing lots of protein, meat preferred, is the best approach to meeting any requirement for taurine in growing children and adults. In the case of babies, mother's milk is best!
That's Taurine and that's no tarus.
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As always it is best to attach a disclaimer to anything that even suggest a medical information. This is not a medical review; it is intended to promote thinking about our diet. Joe Wortham's Home Page , About Joe Wortham