Amino Acid Profile, Qn, Urine (Labcorp)

Alanine is a nonessential amino acid. It is the second most abundant amino acid in circulation, after glutamine. It is found in many foods including eggs, meat, lentils, and fish. Alanine is involved in sugar metabolism for energy and is important in immune system function, specifically T lymphocyte activation. Interestingly, alanine is an agonist that binds to the glycine site of N-methyl-d-aspartate (NMDA) receptors in the brain and improves the positive and cognitive symptoms of patients with schizophrenia.

Allo-isoleucine is nearly undetectable in individuals not affected by maple-syrup urine disease (MSUD). Accordingly, its presence is diagnostic for MSUD, and its absence is sufficient to rule-out MSUD.

Alpha-aminoadipic acid (a-Aminoadipic acid) is an intermediary metabolite of lysine (primarily) and of tryptophan.

Alpha amniobutyric acid (AABA), also known as Alpha-amino-N-butyric acid (A-ANB), is an intermediate formed during the catabolism of methionine and threonine. Increases in AABA occur secondary to elevations of either methionine or threonine. AABA becomes propionic acid via alpha-ketobutyric acid in the presence of adequate amounts of thiamin, vitamin B2(as FAD), vitamin B3(as NAD), lipoic acid and magnesium. Deficiencies of any of these, or vitamin B6, could cause increases in AABA. Elevated or decreased levels of the amino acid may indicate a congenital enzyme defect.

Arginine is found in all protein foods and is very abundant in seeds and nuts. It is considered a semi-essential amino acid during early development, infection/inflammation, or renal and/or intestinal impairment. It has many functions in the body including:

- ammonia disposal in the urea cycle

- immune function

- stimulation of insulin release

- muscle metabolism (creatine/creatinine precursor)

- nitric oxide (NO) formation

- glutamic acid and proline formation

- glucose/glycogen conversion

- stimulation of the release of growth hormone, vasopressin, and prolactin

- wound healing

Because arginine is a precursor for nitric oxide synthesis, it is often used therapeutically in cardiovascular disease for its vasodilatory effects.

Argininosuccinate (aka Arginosuccinic acid) is a basic amino acid. Some cells synthesize it from citrulline, aspartic acid and use it as a precursor for arginine in the urea cycle or Citrulline-NO cycle. The enzyme that catalyzes the reaction is argininosuccinate synthetase. Argininosuccinic acid is a precursor to fumarate in the citric acid cycle via argininosuccinate lyase. Defects in the argininosuccinate lyase enzyme can lead to argininosuccinate lyase deficiency, which is an inborn error of metabolism.

Asparagine is a non-essential protein amino acid that is present in many fruits and vegetables including asparagus, from which it gets its name. Other dietary sources include meat, potatoes, eggs, nuts, and dairy. It can also be formed from aspartic acid and glutamine using the enzyme asparagine synthetase.

In addition to being a structural component of many proteins, asparagine is also useful to the urea cycle. It acts as a nontoxic carrier of residual ammonia to be eliminated from the body. Asparagine is rapidly converted to aspartic acid by the enzyme asparaginase. Interestingly, L-asparaginase has been successfully used as a chemotherapeutic agent for decades.

It causes extracellular depletion of asparagine which seems to play a critical role in cellular adaptations to glutamine and apoptosis.

Aspartic acid is a nonessential amino acid that plays roles in many important metabolic processes, such as energy production (citric acid cycle), hormone metabolism, CNS activation, and the urea cycle. It is found in many protein sources such as oysters, meats, seeds, avocado, asparagus, and beets. It is also an ingredient in artificial sweeteners.

Aspartic acid is a precursor to many amino acids and other molecules like asparagine, arginine, isoleucine, lysine, methionine, isoleucine, threonine, nucleotides, NAD, and pantothenate. Aspartate, like glutamine, can also be considered a neuroexcitatory neurotransmitter since it activates the N-methyl-D-aspartate receptor in the brain.

β-alanine is a breakdown product of carnosine and anserine, which are dipeptides from meat consumption. Although β-alanine’s properties are limited, its relationship to carnosine makes it important. Both have antioxidant properties. And, as previously mentioned, carnosine is critical for pH buffering in skeletal muscle during exercise, but its formation can be limited by enzymatic factors.

For this reason, supplementation with β-alanine is sometimes used to enhance carnitine and therefore improve athletic performance. In addition to diet and supplementation, β-alanine can also be endogenously produced. This occurs via degradation of uracil in the liver but it can also be made by intestinal bacteria such as E. coli.

Beta-aminoisobutyric acid (BAIB) is an amino acid end product of the pyrimidine metabolism. It is excreted in small quantities into the urine in almost all human beings. Thymine, released when RNA and DNA are degraded, enters a catabolic pathway that leads to Beta-Aminoisobutyric Acid.

Citrulline is an intermediate, nonprotein-forming amino acid in the urea cycle serving as a precursor to arginine. It derives its name from the watermelon (Citrullus vulgaris), where it was first isolated and identified.

It is easily absorbed by the gut and bypasses the liver, making it an effective method for repleting arginine.

Other food sources of citrulline include muskmelons, bitter melons, squashes, gourds, cucumbers and pumpkins.

Citrulline can also be synthesized from arginine and glutamine in enterocytes, which can then be metabolized by the kidneys back into arginine.

Cystathionine is an intermediate dipeptide within the process of transsulfuration.

Transsulfuration is the main route for irreversible homocysteine disposal, glutathione production, and energy. The initial step involves the enzyme cystathionine β-synthase enzyme (CBS). This reaction requires nutrient cofactors such as vitamin B6 and iron. Cystathionine is then converted to cysteine, and eventually goes on to either make glutathione or feed the Kreb’s cycle.

Cystine is formed from the oxidation of cysteine, or from the degradation of glutathione oxidation products. It is two cysteines linked together with a disulfide bond.

Gamma-aminobutyrate (GABA) is the major inhibitory neurotransmitter found in the CNS and, as such, is important for balancing excitatory action of other neurotransmitters.

Glutamate is a vital neurotransmitter in the central nervous system, involved in almost all significant excitatory brain functions. It is the primary and most abundant excitatory neurotransmitter, and it's estimated that over half of all neural synapses release glutamate, making it a critical player in neural circuit communication.

Glutamic acid and glutamate are essentially interchangeable terms. The two molecules are almost identical, except that glutamic acid has an additional proton, or hydrogen atom. In physiological conditions, glutamic acid sheds this extra proton and becomes glutamate, the abundant form of the amino acid in the human body.

Glutamate is a crucial excitatory neurotransmitter that plays a vital role in maintaining healthy brain and nervous system function. It enables us to learn, remember, feel, sense, and coordinate our movements effectively.

Glutamine is a nonessential amino acid and is the most abundant amino acid in the body. It is formed from glutamate using the enzyme glutamine synthetase.

Approximately 80% of glutamine is found in the skeletal muscle, and this concentration is 30 times higher than the amount of glutamine found in human plasma. Although glucose is used as fuel for many tissues in the body, glutamine is the main fuel source for a large number of cells including lymphocytes, neutrophils, macrophages, and enterocytes.

Glycine is a nonessential amino acid that is synthesized from choline, serine, hydroxyproline, and threonine.

It has many important physiologic functions. It is one of three amino acids that make up glutathione. Glycine’s dietary sources include meat, fish, legumes, and gelatins.

Glycine is a major collagen and elastin component, which are the most abundant proteins in the body.

Like taurine, it is an amino acid necessary for bile acid conjugation; therefore, it plays a key role in lipid digestion and absorption.

Glycine is the precursor to various important metabolites such as porphyrins, purines, heme, and creatine. It acts both as an inhibitory neurotransmitter in the CNS and as an excitatory neurotransmitter on N-methyl-D-aspartate (NMDA) receptors.

Histidine is a semi-essential amino acid which is formed in the breakdown of carnosine. Red meat is a common source of carnosine, and therefore histadine. 

Other food sources include poultry, fish, nuts, seeds, and grains. Histidine and histamine have a unique relationship. The amino acid histadine becomes histamine via a vitamin B6- dependent enzyme called histidine decarboxylase. 

With this, decreased amounts of histidine and insufficient vitamin B6 can subsequently lead to a decrease in histamine concentration. This may impair digestion, since histamine binds to H2 receptors located on the surface of parietal cells to stimulate gastric acid secretion, necessary for protein breakdown.

Histidine also inhibits the production of proinflammatory cytokines by monocytes and is therefore anti-inflammatory and antioxidant. 

With these beneficial effects, histidine supplementation has been shown to improve insulin resistance, reduce BMI, suppress inflammation, and lower oxidative stress in obese women with metabolic syndrome. 

Interestingly, histadine can also be broken down to form urocanic acid in the liver and skin. Urocanic acid absorbs UV light and is thought to act as a natural sunscreen.

The amino acid homocitrulline is a metabolite of ornithine in human metabolism.

The amino acid can be detected in larger amounts in the urine of individuals with urea cycle disorders. Both amino acids can be detected in urine. Amino acid analysis allows for the quantitative analysis of these amino acid metabolites in biological fluids such as urine, blood, plasma or proteins.

Homocystine is a common amino acid in your blood. You get it mostly from eating meat. High levels of it are linked to early development of heart disease.

Hydroxylysine is an amino acid related to collagen.

What is collagen?

Collagen is the most abundant protein in your body. It is the major component of connective tissues that make up several body parts, including tendons, ligaments, skin and muscles.

- Hydroxyproline is the key factor in stabilizing collagens.

- Hydroxyproline is abundant in meat and low in plant-based foods. Meat intake increases levels of proline and hydroxyproline.

- Increased hydroxyproline has been found in collagen catabolism (bone resorption, increased reactive oxygen species [ROS]), tissue degradation, muscle damage, or other conditions such as Paget's disease or Alzheimer's disease.

- Proline and hydroxyproline both negatively correlated with a higher likelihood of anxiety, depression, and psychoses.

Branched Chain Amino Acids (Isoleucine, Leucine, Valine) are the three branched chain amino acids (BCAAs).

Branched chain amino acids (BCAA) are essential amino acids and must be obtained from the diet (mainly meat, grains, and dairy). 

Not only do the BCAAs account for almost 50% of muscle protein, but they have many metabolic functions. 

BCAAs act as substrates for protein synthesis, energy production, neurotransmitter production, glucose metabolism, and the immune response. They are also involved in stimulation of albumin and glycogen synthesis, improvement of insulin resistance, inhibition of free radical production, and hepatocyte apoptosis with liver regeneration.

Branched Chain Amino Acids (Isoleucine, Leucine, Valine) are the three branched chain amino acids (BCAAs). Branched chain amino acids (BCAA) are essential amino acids and must be obtained from the diet (mainly meat, grains, and dairy).

Lysine is a nutritionally essential amino acid abundant in meat, fish, fowl, and legumes and is needed for formation of body proteins and enzymes.

Lysine can be methylated using S-adenosylmethionine (SAM) to synthesize carnitine, which is needed for fatty acid oxidation. Lysine also generates Acetyl CoA for use in the citric acid cycle. Lysine, proline, hydroxyproline, and vitamin C are important in the synthesis of collagen for skin, bones, tendons and cartilage.

L-lysine supplementation has also been studied for herpes simplex treatment and prophylaxis and may be beneficial.

Methionine is an essential amino acid that plays an important role in the methylation cycle. Methionine is obtained from dietary intake or through homocysteine remethylation. Methionine’s dietary sources include eggs, fish, meats, Brazil nuts, and other plant seeds. 

Methionine is converted to the body’s main methyl donor, S-adenosylmethionine (SAM). This conversion requires the enzyme methionine adenosyltransferase (MAT).

Ornithine is an intermediate nonprotein-forming amino acid of the urea cycle.

Arginine is converted to ornithine via the arginase enzyme, with urea as a byproduct. Ornithine combined with carbamoyl phosphate is then converted into citrulline via the ornithine transcarbamylase (OTC) enzyme. The contribution of carbamoyl phosphate results from the metabolism of ammonia by the enzyme carbamoyl phosphate synthase, and if this magnesium-dependent process is impaired, ammonia buildup, or hyperammonemia can occur.

Ornithine can also form polyamines including putrescine via the ornithine decarboxylase (ODC) enzyme, which requires pyridoxal-5-phosphate (vitamin B6) as a cofactor.

Putrescine and other polyamines are crucial to the growth and proliferation of cells.

Phenylalanine is an essential amino acid found in most foods which contain protein such as meat, fish, lentils, vegetables, and dairy. 

Phenylalanine is the precursor to another amino acid, tyrosine. Because tyrosine is needed to form several neurotransmitters (dopamine, epinephrine, and norepinephrine), as well as thyroid hormone and melanin, phenylalanine intake is important.

Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid.

Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage.

Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn.

Sarcosine is an amino acid made within the methylation cycle when S-adenosylmethionine (SAM) is conjugated with glycine. It can also be made by catabolism of dimethylglycine (DMG).

There are many dietary sources of sarcosine including eggs, legumes, nuts, and meats.

Sarcosine is also available as an over-the-counter supplement, and it is widely used in cosmetic formulations (toothpaste, creams, and soaps) and detergents. In the methylation cycle, sarcosine is created by the GNMT enzyme, which functions to control SAM excess.

Serine is a nonessential amino acid used in protein biosynthesis and can be derived from four possible sources: dietary intake, degradation of protein and phospholipids, biosynthesis from glycolysis intermediate 3-phosphoglycerate, or from glycine.

Serine is found in soybeans, nuts, eggs, lentils, shellfish, and meats. Serine is used to synthesize ethanolamine and choline for phospholipids. Serine is essential for the synthesis of sphingolipids and phosphatidylserine in CNS neurons. In the folate cycle, glycine and serine are interconverted. These methyltransferase reactions and interconversions are readily reversible depending on the needs of the folate cycle. Dietary serine is not fully converted to glycine; therefore, serine supplementation has little value, though is not harmful.

Taurine differs from other amino acids because a sulfur group replaces the carboxyl group of what would be the nonessential amino acid, β-alanine. It takes part in biochemical reactions and is not fully incorporated into proteins. In most tissues, it remains a free amino acid.

Taurine’s highest concentration is in muscle, platelets, and the central nervous system. Taurine is mainly obtained via dietary sources (dairy, shellfish, turkey, energy drinks), but can also come from sulfur amino acid metabolism (methionine and cysteine).

It has been proposed that taurine acts as an antioxidant, intracellular osmolyte, membrane stabilizer, and a neurotransmitter.

Threonine is an essential amino acid, i.e., it is vital for your health, but it cannot be synthesized by your body and therefore has to be obtained from a diet.

Tryptophan is involved in serotonin production via vitamin B6-dependent pathways resulting in the intermediate 5-hydroxytryptophan (5-HTP). 5-HTP is often used as a supplement for serotonin formation instead of tryptophan, which can be quickly metabolized in other pathways.

Serotonin is further metabolized to melatonin via methylation.

Because of these downstream conversions, therapeutic administration of 5-HTP has been shown to be effective for depression, fibromyalgia, binge eating associated with obesity, chronic headaches, and insomnia.

Tyrosine is a conditionally essential amino acid which can come directly from the digestion of dietary protein.

Common food sources include dairy, beans, whole grains, meat, and nuts.

If intake is insufficient, tyrosine can be formed from the essential amino acid phenylalanine using a tetrahydrobiopterin reaction. Tyrosine itself is a precursor to several neurotransmitters including dopamine, epinephrine and norepinephrine. It is also needed to create thyroid hormone and melanin skin pigments.

Branched Chain Amino Acids (Isoleucine, Leucine, Valine) Isoleucine, leucine and valine are the three branched chain amino acids (BCAAs). Branched chain amino acids (BCAA) are essential amino acids and must be obtained from the diet (mainly meat, grains, and dairy).