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AMINO ACIDS AND PROTEIN
June 09, 2005 09:48 AM
AMINO ACIDS AND PROTEIN
Next to water, protein is the most abundant substance in the human body. Complex mega-molecules of protein are the structural building blocks of tissue. The thousands of different proteins in our bodies are composed of 20 molecules called amino acids. In the last 20 years, research has shown the benefits of amino acid supplementation to such diverse areas of human biochemistry as metabolism, enzyme and neurotransmitter production and antioxidant protection. Source Naturals utilizes the latest-breaking research to bring you a highly comprehensive line of amino acid supplements.
DNA provides the instruction manual for life, RNA reads the manual and the genetic information is expressed by proteins. Proteins are the most abundant macromolecules in living cells constituting 50% or more of their dry weight. They create the structure of our cells and tissues, and play an essential role in virtually all of the biochemical events that animate those tissues.
The term "protein" refers to a set of macromolecules that encompasses an extensive variety of structure and function&endash;from helical rods with the tensile strength of steel to elastic sheets to huge molecular machines with hinged jaws that snap closed to hold other molecules in place. Amazingly, all proteins, in their remarkable variety, are built out of a set of 20 simple molecules called amino acids.
Amino acids are one of the four types of small molecules out of which all life is constructed. The other three are: palmitic acid (see "Essential Fatty Acids," page #), adenine and glucose. All amino acids share a common chemical "backbone" which consists of an a -carbon atom to which four substituent groups are bonded: a nitrogen-containing amino group (H2N), a carboxyl group (COOH), a hydrogen atom and an "R" group. The "R" group or side chain (figure #) varies in electric charge, size, structure and solubility in water, giving each amino acid its distinct chemical properties. Since all amino acids (except glycine) contain at least one asymmetrical carbon atom, each one exists in at least two forms: the l form and its mirror image or stereoisomer, the d form. While both forms are found in biological systems, only the l form is present in proteins.
Amino acids are linked together like beads on a string to form proteins, sometimes called peptides because of the peptide bonds that link the amino acids together. They range in size from simple two-amino-acid dipeptides to polypeptides which contain more than 1800 connected amino acids. The chemical backbone of the amino acids and their sequence constitutes the primary structure of a protein. Polypeptide chains then fold into specific 2 and 3-dimensional configurations that are unique for each type of protein. The pattern of folds, along with the chemical nature of the amino acid side chains contained in it, give a protein its characteristic biological activity. For example, the connective tissue proteins collagen and elastin give structure to cellular organelles and tissues, while proteins called enzymes catalyze and facilitate metabolic chemical reactions.
Nine of the 20 amino acids involved in protein synthesis are considered "essential";they cannot be synthesized by the body and must be obtained from food sources. The term "non-essential" is sometimes used to classify the other eleven amino acids. However, this word is perhaps a misnomer; a better term might be synthesizable. These amino acids are just as vital to human metabolism as the "essential" amino acids; so vital that the body can synthesize them. They are, however, more available, more versatile, and more interchangeable.
When the presence or absence of a particular amino acid will determine whether a protein can be created or not, that amino acid is called a rate-limiting factor for that protein. For example, the tripeptide glutathione, a compound that forms an important part of the body's protective mechanisms, is made of the amino acids glutamic acid, glycine and cysteine. Glutamic acid and glycine tend to be plentiful in the diet, and can be easily interconverted. Cysteine is the rate-limiting factor for glutathione; the amount of cysteine in the diet will determine the amount of glutathione that can be manufactured by the body.
Amino acids have a special role to play in brain nutrition, because all neurotransmitters are derived from amino acids or related compounds such as choline. Brain neurotransmitters, specifically, are biochemical keys to the workings of the mind. They are substances that perform chemical transmission of nerve impulses between neurons or between neurons and other cell types such as muscle. They work in the following way: an electric current (or action potential) travels down the length of a neuron, or nerve cell, until it reaches the synapse - a narrow gap between two cells. The incoming nerve impulse triggers the release of neurotransmitter (NT) molecules, which diffuse across the synaptic gap. The neurotransmitter molecules bind with receptor proteins embedded in the membrane of the post synaptic neuron and activate a physiological response. Excitatory neurotransmitters propagate a new action potential while inhibitory NT's inhibit the development of new action potentials.
The amino acid precursors of neurotransmitters are able to cross the blood-brain barrier, a structural feature of brain anatomy that prevents many substances from contacting brain tissue. Thus, it is possible to influence brain metabolism (and therefore emotional states) through the mechanism of neurotransmitter synthesis. The enhancement of neurotransmitter production is one of the most exciting advancements to occur in the field of nutrition in modern times.
A major portion of the amino acid requirement in humans is derived from the proteins in food. Successive proteolytic enzymes attack the peptide bonds, cleaving one amino acid at a time from the polypeptide chain. Ultimately, free amino acids as well as small peptides (especially dipeptides) are absorbed through the mucosal cells of the small intestine. The small peptides are then further hydrolyzed so that only free amino acids enter the liver and portal vein. This sounds like a fairly straightforward process. However, the presence of a particular amino acid profile in a certain food does not guarantee the assimilation of those amino acids when the food is ingested. There are three types of amino acids: acidic, basic and neutral; each of these classes has a different transport mediator. Therefore, there is competition for the carrier between any two amino acids in a certain class, both in the digestive tract and at the blood-brain barrier. Thus, the isolation of "free-form" amino acids is an important aid to nutritional engineering. In many cases, the consumption of high potencies of a particular amino acid allows that nutrient to overwhelm the competition for absorption. The resulting increase in blood and tissue levels will yield the benefits conferred by that nutrient.
The isolation of free-form amino acids is an important advancement in the field of nutrition science. Amino acid supplements offer a broad range of choices to complement your nutritional program.