Toxic levels of ammonia may accumulate

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Home > Amino Acids Home

What are Amino
Acids and What Do They Do?

Amino acids are the
chemical units or "building blocks,"
as they are popularly called, that make up proteins. They also are the
end products of protein digestion, or hydrolysis. Amino acids contain
about 16 percent nitrogen. Chemically, this is what distinguishes them
from the other two basic nutrients, sugars and fatty acids, which do
not contain nitrogen.

To understand how vital
amino acids are, you must
understand how essential proteins are to life. It is protein that
provides the structure for all living things. Every living organism,
from the largest animal to the tiniest microbe, is composed of protein.
And in its various forms, protein participates in the vital chemical
processes that sustain life.

Proteins are a
necessary part of every living cell in
the body. Next to water, protein makes up the greatest portion of our
body weight. In the human body, protein substances make up the muscles,
ligaments, tendons, organs, glands, nails, hair, and many vital body
fluids, and are essential for the growth of bones. The enzymes and
hormones that catalyze and regulate all bodily processes are proteins.
Proteins help to regulate the body’s water balance and maintain the
proper internal pH. They assist in the exchange of nutrients between
the intercellular fluids and the tissues, blood, and lymph. A
deficiency of protein can upset the body’s fluid balance, causing
edema. Proteins form the structural basis of chromosomes, through which
genetic information is passed from parents to offspring. The genetic
"code" contained in each cell’s DNA is actually information for how to
make that cell’s proteins.

Proteins are chains of
amino acids linked together by
what are called peptide bonds. Each individual type of protein is
composed of a specific group of amino acids in a specific chemical
arrangement. It is the particular amino acids present and the way in
which they are linked together in sequence that gives the proteins that
make up the various tissues their unique functions and characters. Each
protein in the body is tailored for a specific need; proteins are not

The proteins that make
up the human body are not
obtained directly from the diet. Rather, dietary protein is broken down
into its constituent amino acids, which the body then uses to build the
specific proteins it needs. Thus, it is the amino acids rather than
protein that are the essential nutrients.

In addition to those
that combine to form the body’s
proteins, there are other amino acids that are important in metabolic
functions. Some, such as citrulline, glutathione, ornithine, and
taurine, can be similar to (or byproducts of) the protein-building
amino acids. Some act as neurotransmitters or as precursors of
neurotransmitters, the chemicals that carry information from one nerve
cell to another. Certain amino acids are thus necessary for the brain
to receive and send messages. Unlike many other substances,
neurotransmitters are able to pass through the blood-brain barrier.
This is a kind of defensive shield designed to protect the brain from
toxins and foreign invaders that may be circulating in the bloodstream.
The endothelial cells that make up the walls of the capillaries in the
brain are much more tightly meshed together than are those of
capillaries elsewhere in the body. This prevents many substances,
especially water-based substances, from diffusing through the capillary
walls into brain tissue. Because certain amino acids can pass through
this barrier, they can be used by the brain to communicate with nerve
cells elsewhere in the body.

Amino acids also enable
vitamins and minerals to perform
their jobs properly. Even if vitamins and minerals are absorbed and
assimilated by the body, they cannot be effective unless the necessary
amino acids are present. For example, low levels of the amino acid
tyrosine may lead to iron deficiency. Deficiency and /or impaired
metabolism of the amino acids methionine and taurine has been linked to
allergies and autoimmune disorders. Many elderly people suffer from
depression or neurological problems that may be associated with
deficiencies of the amino acids tyrosine, tryptophan, phenylalanine,
and histidine, and also of the branched-chain amino acids—valine,
isoleucine, and leucine. These are amino acids that can be used to
provide energy directly to muscle tissue. High doses of branched-chain
amino acids have been used in hospitals to treat people suffering from
trauma and infection. Some people are born with an inability to
metabolize the branched-chain amino acids. This potentially
life-threatening condition, branched-chain ketoaciduria (often referred
to as maple syrup urine disease because keto acids released into the
urine cause it to smell like maple syrup) can result in neurological
damage and necessitates a special diet, including a synthetic infant
formula that does not contain leucine, isoleucine, or valine.

There are approximately
twenty-eight commonly known
amino acids that are combined in various ways to create the hundreds of
different types of proteins present in all living things. In the human
body, the liver produces about 80 percent of the amino acids needed.
The remaining

20 percent must be
obtained from the diet. These are
called the essential amino acids. The essential amino acids that must
enter the body through diet are histidine, isoleucine, leucine, lysine,
methionine, phenylalanine, threonine, tryptophan, and valine. The
nonessential amino acids, which can be manufactured in the body from
other amino acids obtained from dietary sources, include alanine,
arginine, asparagine, aspartic acid, citrulline, cysteine, cystine,
gamma-aminobutyric acid, glutamic acid, glutamine, glycine, ornithine,
proline, serine, taurine, and tyrosine. The fact that they are termed
"nonessential" does not mean that they are not necessary, only that
they need not be obtained through the diet because the body can
manufacture them as needed. And nonessential amino acids can become
"essential" under certain conditions. For instance, the nonessential
amino acids cysteine and tyrosine are made from the essential amino
acids methionine and phenylalanine. If methionine and phenylalanine are
not available in sufficient quantities, cysteine and tyrosine then
become essential in the diet.

The processes of
assembling amino acids to make
proteins, and of breaking down proteins into individual amino acids for
the body’s use, are continuous ones. When we need more enzyme proteins,
the body produces more enzyme proteins; when we need more cells, the
body produces more proteins for cells. These different types of
proteins are produced as the need arises. Should the body become
depleted of its reserves of any of the essential amino acids, it would
not be able to produce the proteins that require those amino acids. An
inadequate supply of even one essential amino acid can hinder the
synthesis, and reduce body levels, of necessary proteins. This can
result in negative nitrogen balance, an unhealthy condition in which
the body excretes more nitrogen than it assimilates. Further, all of
the essential amino acids must be present simultaneously in the diet in
order for the other amino acids to be utilized—otherwise, the body
remains in negative nitrogen balance. A lack of vital proteins in the
body can cause problems ranging from indigestion to depression to
stunted growth.

How could such a
situation occur? More easily than you
might think. Many factors can contribute to deficiencies of essential
amino acids, even if you eat a well-balanced diet that contains enough
protein. Impaired absorption, infection, trauma, stress, drug use, age,
and imbalances of other nutrients can all affect the availability of
essential amino acids in the body. Insufficient intake of vitamins and
minerals, especially vitamin C, can interfere with the absorption of
amino acids in the lower part of the small intestines. Vitamin B6 is
needed also, for the transport of amino acids in the body.

If your diet is not
properly balanced—that is, if it
fails to supply adequate amounts of the essential amino acids—sooner or
later, this will become apparent as some type of physical disorder.
This does not mean, however, that eating a diet containing enormous
amounts of protein is the answer. In fact, it is unhealthy. Excess
protein puts undue stress on the kidneys and the liver, which are faced
with processing the waste products of protein metabolism. Nearly half
of the amino acids in dietary protein are transformed into glucose by
the liver and utilized to provide needed energy to the cells. This
process results in a waste product, ammonia. Ammonia is toxic to the
body, so the body protects itself by having the liver turn the ammonia
into a much less toxic compound, urea, which is then carried through
the bloodstream, filtered out by the kidneys, and excreted.

As long as protein
intake is not too great and the liver
is working properly, ammonia is neutralized almost as soon as it is
produced, so it does no harm. However, if there is too much ammonia for
the liver to cope with—as a result of too much protein consumption,
poor digestion, and /or a defect in liver function—toxic
levels may
Strenuous exercise also tends to promote the
of excess ammonia. This may put a person at risk for serious health
problems, including encephalopathy (brain disease) or hepatic coma.

Abnormally high levels of urea can also cause problems, including
inflamed kidneys and back pain. Therefore, it is not the quantity but
the quality of protein in the diet that is important (see DIET AND
NUTRITION in Part One).

It is possible to take
supplements containing amino
acids, both essential and nonessential. For certain disorders, taking
supplements of specific amino acids can be very beneficial. When you
take a specific amino acid or amino acid combination, it supports the
metabolic pathway involved in your particular illness. Vegetarians,
especially vegans, would be wise to take a formula containing all of
the essential amino acids to ensure that their protein requirements are



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