Alpha Nutrition's Nutrition Center
Proteins and Amino Acids
Alpha Nutrition Health Education
From the Alpha Nutrition Program and Nutrition Notes
Related topics
Dietary Guidelines
Vitamins
These discussions of nutrients and nutrition are continued in the Alpha Nutrition Program, Nutrition Notes and other publications in this series.
Four texts are included Professional Starter Pack
Food supplies the building materials to permit continuous cellular renewal and growth. Protein forms a major part of our structure. Most of our body protein is recycled and we do well by ingesting very little protein. About 3% of the total body protein is recycled every day (approximately 200 grams). In a healthy adult, net protein loss in a day may be as low as 2 grams.
Dietary requirements for protein increase with activity, growth, and protein losses, especially following injury or during illness. The average American diet supplies 11-14% of total calories as protein, or 25-300 gms/day. Protein digestion and absorption are generally efficient. A minimum average protein intake is approximately 25 grams.
Since all amino acids contain a nitrogen atom (N), protein balance is synonymous with nitrogen balance. When nitrogen intake exceeds nitrogen loss, there is net protein synthesis. Anabolism, or tissue construction, prevails. When nitrogen losses exceed intake, protein tissue is being broken down and catabolism prevails. Loss of protein-tissues occurs with malnutrition, following surgery, injury, and chronic illness.
Adequate intake of energy molecules, both carbohydrate and fats, is said to "spare protein", permitting a small protein intake to maintain positive nitrogen balance. In metabolic studies, the total amount of nitrogen intake is compared with the total excretion of nitrogen to assess protein balance. Excess amino acids may be converted to fuel.
When amino acids are "burned" as a fuel, ammonia (NH3] is the waste product. Ammonia must be carried to the liver, converted to urea and excreted by the kidneys. One of the penalties of amino acid excess is ammonia excess, a potential cause of body malfunction following a high protein meal. The blood measurement of urea nitrogen (BUN) shows the balance between urea production by the liver and excretion by the kidneys. The BUN rises in kidney failure and serves as a measure of ammonia or nitrogen. In liver disease, reduced ability to synthesize urea leads to ammonia accumulation. Ammonia is neurotoxic and contributes to the syndrome of brain dysfunction in liver failure, hepatic encephalopathy.
Patients with reduced kidney or liver function are required to restrict protein, since their ability to handle the nitrogen waste of oxidized amino acids is limited. Fluctuating levels of ammonia influences brain cell function; they should be considered whenever brain function is abnormal. Some children are born with metabolic abnormalities in the handling of amino acids and ammonia. They often present with malfunctioning brains.
Molecular assembly and molecular disassembly are essential procedures of life. The synthesis of complex structures from a finite set of raw materials underlies the prodigious complexity of life on earth. Control of molecular behavior is achieved by an elite class of protein molecules. Enzymes know how to grab other molecules and break them apart or stick them together, according to the very specific blueprint, contained in DNA molecules. Enzymes themselves are made by other enzymes from the amino acids which food proteins provide. There are about two thousand different enzymes. The largest enzyme populations live inside cells where they are attached to molecular assembly structures. Other enzymes are secreted into body spaces as mobile chemical workers.
Many enzymes become popular after someone writes an article praising their wonderful abilities to manipulate molecular behavior - ingestion of the enzyme is usually recommended. Superoxide dysmutase is one popular enzyme which cannot be delivered by oral intake to the intercellular sites where it does its useful things. Ingested proteins tend to get digested, losing their information as shape and function, or, if they are not digested, tend to cause allergic reactions rather than functioning normally. The next development of molecular engineering will be vehicles to deliver enzymes to intracellular sites where they will be useful. Delivery vehicles may be physical structures or carrier molecules that protect the enzymes while directing them through the GIT, circulation, and filtering systems like the liver and lungs.
Amino acids are the alphabet characters of body proteins. Proteins are chains of amino acids linked together like beads on a necklace. The individual amino acids fall into two groups: the essential AA's, which must be ingested, and the non-essential AA's, which can be synthesized in the body and need not appear in the food. A total of 9 amino acids are considered essential, while another 11 or so can be synthesized from the essential amino acids. There are other amino acids which appear in nature that are not included in protein structure. These odd amino acids appear especially in plants, where they may have roles as insect deterrents. An occasional non-nutrient amino acid may be useful in the food supply as an accessory nutrient -taurine is a prime candidate.
Essential amino acids :
histidine, isoleucine,leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
Nonessential amino acids:
alanine, arginine, aspartic acid, cystine, glutamic acid, glycine, proline, serine,,tyrosine
Possible accessory nutrient amino acids
taurine l-ornithine
Life is an exercise in molecular synthesis and control. The programs which determine us are coded in the DNA molecules housed in the nucleus of every cell. The DNA code consists of strings of 64 alphabet characters which specify amino acids in groups of three characters (codones). A single character is a base pair which is visualized as the rung on a ladder, twisted into a helix. The entire range of cellular procedures of life consists of stringing amino acids together. The DNA alphabet (blueprint) is first translated into enzyme synthesis. Enzymes, in turn, orchestrate and control the synthesis of all molecules (construction procedures). This is a elegant, simple plan which permits the evolution of great complexity. Molecular management takes the form:
DNA---->RNA----> Enzyme Proteins
enzyme
Molecule 1 + Molecule 2 ---------> Products
vitamin + mineral cofactors
The amino acid sequence in a protein is read from the DNA molecule and transferred to the protein synthesis machinery in a cell by transfer RNA. The protein synthesis centers in cells are known as Ribosomes. Ribosomes develop an RNA template for the protein to be manufactured and draw free amino acids from the cellular pool into an orderly sequence. The ordered amino acids are then linked by enzymatic action to form another protein. The link between amino acids is as a peptide bond. The "Amino" of amino acids is a nitrogen-hydrogen group, NH2. Every amino acid has NH2 at one end and COOH, the acid, at the other end. The peptide bond links the NH2 with the COOH like this:
...CO-NH-OC...
When the peptide bond is made, a surplus of two hydrogen and one oxygen atom is removed - H2O, or water. We use a 3-letter abbreviation of the amino acid name to write an amino acid sequence which is the primary structure of a peptide or protein: Gly-Leu-Gly-Try-..is a 4 amino acid sequence. Short chains of amino acids are peptides; longer chains are polypeptides. Even longer chains are proteins. Peptides assume information characteristics at 3 or more AA lengths. As the AA chain elongates, its shape becomes more complex and more meaningful. A typical globular protein has about 350 amino acids. The long amino acid chains of proteins are folded into a shaped object. The shape is known as the tertiary structure of the protein.
Protein shape is information. The shape may determine where the protein can go in a cell or which biological membrane will let it pass. The shape determines its structural role. The shape of a protein is also its identity. Shape ID is recognized and remembered by the immune system and is the basis of the body's immune defense. A small error in the DNA code results in a large manufacturing error. The study of individual enzyme defects has given us insights into the control of molecular assembly. If a single gene, encoding the procedures for a single protein, is defective, the protein is missing or does not function properly.
Amino Acid Requirements & Intolerances
The need for specific amino acids is difficult to determine. There is a wide range of needs and tolerances among different individuals. Amino acids appear to be relatively easy to obtain in adequate amounts, even on simple vegetarian diets with no meat, fish, eggs, or milk, provided that different vegetables are combined. Mixing a legume with a grain or with a tuber should provide a complete amino acid mixture, as well as a good variety of vitamins and minerals.
Protein-deficiency anxiety is not well-founded in affluent countries. Some of the non-essential AA's may become essential if their synthesis is blocked by enzyme deficiencies. In order for protein synthesis to proceed, all the amino acids must be supplied at the same time. Since we are mammals, all mammalian proteins tend to have the same set of AAs as our own. Plant proteins may be deficient in lysine, threonine, and tryptophan. Vegetables should be combined to achieve a complete the AA set. Corn or maize, for example, is deficient in lysine, although many years of corn-breeding research have produced hybrid corns with increased lysine content. The substitution of the newer corn hybrids may eliminate protein malnutrition where this is a staple plant.
Some patients on very limited diets (rice and a few vegetables alone, for example) seem to ingest sufficient essential amino acids to remain well, at least for several months even though their food may be deficient in essential AAs. A minimal diet presents minimal problems to one's metabolism. A protein deficient diet may be better tolerated than a protein excess diet.
We have thought a lot about the relationship between the food intake of protein and the intakes of pure amino acids in one of our elemental nutrient formulas. A naive assumption is that amino acid intake and protein intake are the same. If you decide that a patient needs 75 Grams of protein per day and you want to replace the protein with amino acids, you assume you have to give them 75 grams of amino acids. Not so.
If you look at RDA values for protein, you get the wrong idea that amino acid intake level has to the same as protein intake but we believe that a daily intake of 25 grams of free form amino acids will be adequate for most people, most of the time. RDA protein values are crude approximations based on food protein values. The proteins in foods have to be digested into dipeptides and free amino acids before nutrients are available and protein digestion is incomplete Some percentage of food protein is wasted in the digestive tract.
The trick is that if amino acids arrive in high concentrations, the liver is obligated to destroy most of them; so that high protein intake is wasteful if you want the amino acids to be utilized as protein building blocks and as neurotransmitter substrates.
Second, you have to know that the body recycles amino acids and becomes every efficient when protein intake is low; the loss of amino acids can drop to about 2 grams per day.
Third, you have to know that amino acid proportioning is relevant to how amino acids are admitted to cells and how they are utilized. The concept of protein quality is used to express the idea that all the 9 essential amino acids have to be present before any of them can be used to make proteins. Plants may have incomplete amino acids sets, for example, and protein deficiency symptoms can appear even when the protein intake is adequate.
On the positive side of the equation, if a completely available, precisely engineered amino acid set is available, the total daily requirement is lower the RDA values for food protein intake As a rule of thumb we recommend calculating the RDA protein requirement in Grams and supplying 30 % to 50% of that value as Alpha AAX, a blend of amino acids (available separately in Alpha AAX or combined with other nutrients in Alpha ENF, Alpha PMX, and Alpha DMX.)