On the one hand, amino acids are the smallest building blocks of a protein, but on the other hand they also fulfil independent functional tasks. The amino acids that are used to build proteins are called "proteinogenic".

A distinction is also made between essential and non-essential amino acids:

• Essential amino acids: Must be supplied through food; a deficiency cannot be compensated by the body itself
• Non-essential amino acids: Can be formed in the organism by consuming essential amino acids

More than 400 amino acids are known to date, 20 of which are "proteinogenic" in humans - ie they are used to build proteins. And 9 of the >400 amino acids are "essential", ie they must be supplied through food and cannot be produced by the body itself.

Amino acids are fatty acid derivatives (carboxylic acid derivatives) with an amino group on the α-C atom (“α-amino carboxylic acids”)

Classification of Amino Acids

• According to chemical structure
  • branched-chain or non-branched-chain
  • sulfur-containing or non-sulfur-containing
  • aromatic (with a benzene ring of 6 C atoms in the side chain) or aliphatic (non-aromatic)
• According to Essentiality
  • Essential/semi-essential AS (must be supplied)
  • Non-essential AS (can be formed e.g. in the citric acid cycle by transamination from 2-oxocarboxylic acids)
• By tasks
  • Functional tasks:
    • Structural tasks (anabolic function): construction of oligopeptides and proteins (currently 23 amino acids recognized, e.g. ornithine, citrulline, taurine)
    • energy production (catabolic function)
    • provision of sulfur
  • Medical tasks:
    • Prevention, e.g. hormone replacement therapy (L-arginine)
    • Therapy, e.g. Immunology, Oxidative Stress, Cardiology, Psyche

The most important amino acids

a) Essential

• Isoleucine (VK, k, g, *)
• Leucine (VK, k, *)
• Lysine (k, *)
• methionine (SH, g, *)
• Phenylalanine (AS, k, g, *)
• Threonine (g, *)
• Tryptophan (AS, k, g, *)
• Valine (VK, g, *)
• Histidine (AS, g, *

b) Semi-essential

• Arginine (g *)
• Cystine/Cysteine ​​(SH, g, *)
• Tyrosine (AS, k, g, *)

c) Non-essential

• Alanine (g, *)
• aspartic acid/
• asparagine (g, *)
• Glutamic acid (g, *)
• Glutamine (g, *)
• Glycine (Glycocoll, g, *)
• serine (g, *)
  proline (g, *)
  ornithine
• taurine (SH)
• hydroxyproline
• citrulline
• 3-methylhistidine
• GABA
• theanine

* = AA used for protein synthesis
k = ketogenic
g = glycogen
SH = sulfur-containing AS
VK = Branched-chain AA
AS = Aromatic AS

Catabolic vs anabolic pathway

Digestible proteins that are ingested through food are broken down into their components (amino acids) and added to the amino acid pool. The amino acids are then utilized either “catabolically” or “anabolically”.The catabolic pathway describes the use of amino acids to generate energy in the mitochondria; the anabolic pathway describes the use of amino acids to build proteins.

Functions of proteins (formed from amino acids) in humans

protein	function	examples
structural proteins	supporting structure of the organism	Collagen, hair, nails, matrix, elastin, keratin, myosin
Contractile proteins	components of the muscles	myosin, actin
enzymes	Catalysis of many biochemical reactions, antioxidant and anti-inflammatory function	Amylase, lipase, pepsin, trypsin, catalases, peroxidases, proteases
transport and carrier proteins	transport of important molecules	Hemoglobin, plasma albumins, calcium-binding protein, metallothioneins
regulatory proteins	control and coordination of chemical reactions	Hormones (e.g.insulin, oxytocin, insulin, glucagon, corticotropin, vasopressin, angiotensin)
protective proteins	Storage of substances for future use	Blood coagulation (thrombin, fibrin, fibrinogen), immune system (immunoglobulins, interleukins), storage proteins (ferritin = iron storage)
control proteins	regulation of various processes in the organism	Correct reading of DNA

Amino acids as precursors of endogenous substances

precursors of other AS derivatives (oligopeptides)
Lysine + Methionine	carnitine
Phenylalanine + Tyrosine	coenzyme Q10
Glutamate + Glycine + Cysteine	glutathione
Arginine + Glycine (+ cofactor methionine)	Creatine (methylguanidine acetic acid)
Cysteine ​​(+ Vit B5 + ADP)	coenzyme A
Glutamate + Glycine + Cysteine ​​(+ Vit B3 + Chromium)	glucose tolerance factor
arginine, ornithine (+ SAM)	Polyamines (spermidine, putrescine, spermine)
arginine	nitric oxide (NO)

precursors of neurotransmitters (biogenic amines)
Phenylalanine -> Tyrosine	Adrenaline, noradrenaline, thyroxine, tyramine (sympathomimetic)
tryptophan	serotonin, melatonin
histidine	histamine
glutamic acid (glutamate)	gamma-aminobutyric acid (GABA), glutamine

The most important amino acids at a glance

L-lysine

• essential amino acid
• basic amino acid
• carnitine building block (cofactors Fe, Vit. C, B3)
• Effects:
  • cardiovascular protective function: building block of vascular collagen, atherogenic potential of Lp(a) â, possible release of deposited Lp(a)'s
  • Important for the immune system (especially in viral infections (reduces virus replication))
  • Increases intestinal Ca++ absorption (possiblyuseful for osteoporosis)

L-methionine

• essential amino acid
• Neutral sulfur-containing amino acid (main sulfur source)
• S-adenosyl-methionine (SAM) = biologically active form
• Precursor of homocysteine ​​and thus of cysteine, cystine, taurine (B vitamins and methionine are essential for homocysteine ​​metabolism and 1-carbon pathway!)
• building block of carnitine
• Effects:
  • Most important methyl group donor and thus highly relevant in the context of epigenetics and longevity research (“healthy longevity”)
  • binds heavy metals for detoxification (e.g. copper, cadmium and mercury)
  • acidifies the urine
  • has an antioxidant effect (supports selenium effect)
  • important for the immune system

L-tryptophan

• essential amino acid
• aromatic amino acid
• precursor of serotonin (and melatonin)
• precursor of kynurenine formation
• Effects:
  • sleep-promoting
  • immune system
    • antibody response via kynurenine
    • Monocytes and IL1 production á
  • Formation of vitamin B3 (niacin) or NAD via kynurenine (mainly in the liver)
  • formation of proteins and acetyl-CoA
  • Blood pressure lowering (especially in combination with Vit. B6): probably through serotonergic effects
• Risk of deficiency e.g. in cases of fructose intolerance and lactose intolerance (reduced absorption in the intestine), because undigested lactose binds tryptophan and prevents its absorption
  (Source: www.fxmayr.com/de/medizin-ernaehrung-lactose.aspx; https://vgxii.com/attack-of-the-tryptophan/)

Tryptophan-serotonin-melatonin synthesis

L-arginine

• semi-essential amino acid
• Basic amino acid formed from citrulline and aspartate or from ornithine
• effects:
  • precursor of nitric oxide (NO)
    • signaling substance
    • antioxidant, cytotoxic, antimicrobial, stimulation of neutrophil leukocytes
    • vasodilating, reduces platelet aggregation and blood pressure, improves blood circulation (similar to prostaglandin E1)
  • Stimulated anabolic somatotropin (STH = "Hormone of Fasting"); STH increases protein synthesis and mobilizes fat deposits
  • Stimulates anabolic insulin like growth factor 1 (IGF-1)
  • Important for (cellular) immune system
  • Important for collagen synthesis
  • Improves perfusion after ischemia
• Practical tip:
  • Fractionated administration in several small doses between meals
  • Herpes proteins rich in arginine (possiblyactivation of latent infections):
    Therefore, arginine is not used as monotherapy for herpes simplex infections:
    Combination with lysine (acute 3x1 g/day, preventive 500 mg/day) in a ratio of 1:2

L-carnitine

• amino acid derivative
• formation from methionine and lysine
• Effects:
  • Energy metabolism (L-carnitine as a “biocarrier”): Transport molecule for free long-chain FA in mitochondria for beta-oxidation (95% of occurrence in heart and skeletal muscle)
  • Performance-enhancing (e.g. sports, cardiology)
  • influence on blood lipid levels
  • membrane-stabilizing, antioxidant and neuroprotective
  • Important for the immune system
  • detoxification function: Liver metabolism of toxic substances; transport molecule (“biocarrier”) of toxic metabolites for excretion via kidney

coenzyme Q10

• amino acid derivative
• Formation from geranylgeranyl phosphate (from mevalonic acid pathway or acetyl-CoA via all-trans-decaprenyl phosphate) and from tyrosine (via hydroxybenzoic acid)
• Effects:
  • Energy metabolism: Central component of the respiratory chain (inner mitochondrial membrane)
  • antioxidant in lipophilic phase (concerning arteriosclerosis, cancer, accelerated aging, etc.))
    • Localization in mitochondria: particularly good and rapid local effect on oxygen radicals
    • Involved in the reduction of oxidized vitamin E
  • Attention: Statin administration reduces coenzyme Q-10 formation (from mevalonic acid)

Examples of amino acid (and derivative) indications

A) immune system

• Amino acids are building blocks of immune cells
• Amino acids are building blocks of:
  • immunoglobulins
  • Interferons (antiviral and antiproliferative glycoproteins of leukocytes)
  • interleukins (stimulate growth and differentiation of lymphocytes)
  • Lysozyme (dissolves bacterial walls)
  • Thymus factors (stimulate maturation of T lymphocytes and proliferation of lymph tissue)
• Amino acids (and derivatives) have an antioxidant effect
• Amino acids stabilize the nonspecific mucosa block
• Amino acids affect T cell regulation
• Amino acids stimulate the specific humoral immune response
• Tryptophan is a kynurenine precursor

substance	effect examples
arginine	T-cell stimulation, phagocytosis modulation (neutrophils, monocytes), antimicrobial, regulation of cytokine production
lysine	regulation of NO
methionine	methyl group donor in the immune system
taurine	anti-inflammatory
threonine	Stimulation of lymphocyte proliferation, synthesis of mucus protein in the intestinal immune system,
tryptophan	Inhibition of pro-inflammatory cytokines, production of kynurenines, increase in immunity
carnitine	T cell stimulation, phagocytosis modulation (neutrophils, monocytes)
glutathione	Regulation of cell metabolism (e.g. leukotriene formation, apoptosis), immune response
creatine	Antiviral activity

(Source: Arndt & Albers, Handbook of Protein and Amino Acids, p. 55, Li P et al.; Amino acids and immune function.Br J Nutr 2007;98(2):237-52)

B) Diabetes

• Increased use of amino acids for gluconeogenesis (amino acids as energy carriers)
• Increased formation of fatty acids and ketone bodies from amino acids (due to high amounts of acetyl-CoA and overload of the citric acid cycle)
• Amino acid derivatives have an antioxidant effect (in cases of high oxidative stress)
• Amino acids can stimulate insulin secretion (insulin improves amino acid uptake in cells)
• Insulin (peptide hormone) contains disulfide bridges and requires sulfur
• Important amino acids for diabetes:
  • L-carnitine (reduces acetyl-CoA and lowers ketone bodies)
  • L-arginine, phenylalanine, BCAA (insulin secretion)
  • L-cysteine ​​(among other things, component of GTF, essential for CoA formation, S supplier)
  • Aspartic acid (lowers ketone bodies)
  • Glutathione, taurine (antioxidant, S supplier)

C) Cardiovascular system

• Amino acids are relevant in the cardiovascular system for
  • vasodilation ("expansion" of blood vessels)
  • vascular protection
  • energy supply
  • radical degradation and reduction of lipid peroxidation
• Important amino acids for the cardiovascular system:
  • L-arginine (NO and vasodilation)
  • L-cysteine ​​(improves NO function)
  • Taurine (positive inotropic, antiarrhythmic, antioxidant)
  • L-lysine (stabilizes vascular walls, reduces atherogenic potential of Lp(a))
  • L-tryptophan and tyrosine (BP-lowering neurotransmitters)
  • L-carnitine and coenzyme Q10 (energy)
  • Glutathione (antioxidant)

D) Liver

• Amino acids prevent destruction of the (liver) cell membrane
• formation of structural proteins (e.g. liver cell membrane)
• formation of liver-specific enzymes and functional proteins
• Amino acids maintain complex detoxification functions: liver must detoxify ammonia in the urea cycle (formed during protein catabolism)
• Important amino acids for the liver:
• L-arginine, ornithine, aspartic acid, citrulline
• L-cysteine ​​(sulfate, glutathione)
• Branched-chain AA (in cirrhosis)

E) Gastrointestinal tract

• Proteins are broken down in the gastrointestinal tract:
  • Protein digestion begins in the stomach
  • Pepsin as a key enzyme (acid-controlled)
  • Peptones as cleavage products (stimulate duodenal cholecystokinin and exocrine pancreas)
• absorption disorders (e.g. due to diseases) lead to amino acid deficiency
• The intestine needs amino acids for its function (e.g.cell membrane structure, energy for intestinal flora, detoxification, bile acid metabolism)
• Important amino acids (derivatives) with intestinal mucosa-protecting and digestive-promoting effects: methionine, glutamine, histidine, threonine, tryptophan and glutathione

Lead amino acids (and derivatives) in the gastrointestinal tract

substance	Functions & Effects
methionine	Cofactor in the formation of melatonin and CoA (involved in the formation of cell membrane phospholipids of the intestinal mucosa) Important for formation of active short-chain fatty acids (formed by physiological intestinal flora with mucosaprotective and anticarcinogenic properties) Important for barrier function and integrity of the colon mucosa
glutamine	main energy source of the mucosal cells and precursor for the nucleotide biosynthesis of rapidly dividing intestinal mucosa cells. Improves intestinal mucosa. Metabolic stress (surgery, burns, trauma) often leads to glutamine deficiency, which leads to mucosal atrophy with reduced barrier function and facilitated bacterial translocation
histidine	Influences gastric acidity and is the starting substance for histamine formation (biogenic amine with many biological effects). Increases hydrochloric acid secretion
threonine	Promotes mucosal integrity and barrier function
tryptophan	Precursors of serotonin and indole (derivatives) that support barrier function and mucosal homeostasis and nervous system
glutathione (Cysteine, Glycine, glutamic acid)	Essential for maintaining normal intestinal mucosa. Antioxidant. Important for detoxification. Diseases and noxious substances such as celiac disease, cigarette smoke, cytostatics and NSAIDs worsen the intestinal glutathione balance

F) Psyche

• precursors and activators of neurotransmitters (L-Tryptophan, L-Phenylalanine, L-Tyrosine, L-Histidine)
• effect as a neurotransmitter (e.g.glutamine, glutamate, GABA, glycine)
• Involved in the metabolism of melatonin (SAM, L-tryptophan)
• Incorporated as protein precursors in Stress processing, hypothalamic-pituitary-adrenal axis and sleep

neurotransmitters	precursor	function / control
L-glycine	L-serine	inhibitory effect on brain activity (anxiolysis, sedation)
L-glutamic acid (glutamate)	L-glutamine	Excitatory NTM (brain alertness); important for neuroplasticity
L-glutamine	L-glutamic acid (glutamate)	Can be converted into glutamic acid; precursor of GABA; important for cellular immune defense
GABA (γ-aminobutyric acid)	L-glutamic acid (glutamate)	Inhibitory NTM (sleep-inducing, anxiolytic, sedative, HGH-stimulating)
adrenaline/noradrenaline	L-phenylalanine/L-tyrosine	More excitatory NTM
serotonin	L-tryptophan	More inhibitory NTM
histamine	L-histidine	Has a regulating effect on noradrenergic, serotoninergic, cholinergic, dopaminergic and glutaminergic neurons; influenced by presynaptic H3 receptors release of other NTM

G) Weight reduction

• Weight reduction means: reducing calorie intake; consequences:
  • Lower protein intake
  • Gluconeogenesis and fatty acid production from amino acids á
  • Degradation of structural proteins (muscles, enzymes, immunoglobulins, transport albumin) à reduced performance, tiredness, fatigue, premature "diet termination"
  • Colloid osmotic pressure decreases with edema formation and reduced diuresis (amino acids regulate water balance)
  • Important amino acids in a diet:
    • Neurotransmitters and precursors (e.g. tryptophan, phenylalanine, glutamine, taurine)
    • Arginine (activation of the somatotrophic hormone STH à reduces fat mass)
    • Carnitine (fat burning)

H) Sport / Performance

• structural development (especially muscles)
• Optimization of metabolism (e.g. immune system, redox system, psyche)
• energy generation (including reserve energy)
• Antioxidative effect (high levels of radicals during extreme sports
• Important amino acids to increase performance:
  • L-carnitine (energy)
  • Coenzyme Q 10 (energy)
  • Creatine (energy)
  • Glutathione (antioxidant)
  • Essential AS in particularbranched-chain AA as well as arginine, glutamine (structural building)

I) Healthy Longevity

• A good supply of amino acids is a useful building block in an overall concept of “good aging”
  • Amino acids are building blocks of proteins and other essential substances
  • Optimization of metabolism (e.g. immune system, redox system, psyche, hormones)
  • optimization of the supporting tissue
  • Optimization of organ functions (e.g. cardiovascular, nerves, skin)
• Important amino acids for “aging skin” (e.g.dryness, wrinkles, collagen deficiency, healing)
  • arginine
  • cysteine
  • proline
  • Glycine
  • mix of essential amino acids
  • spermidine

Symptoms of amino acid and protein deficiency

• Swollen eyes and legs (water from blood vessels shifts into tissue)
• Muscles become weaker (muscle loss)
• Hair becomes thinner (due to lack of keratin)
• Nails become brittle
• Skin becomes dry and flaky (wrinkles)
• Mental alertness decreases
• fatigue and sleep disorders
• immune deficiency (susceptibility to infection)
• wound healing disorders
• micronutrient deficiency (protein transports micronutrients)
• Blood sugar fluctuations and cravings for sweets (feeling of lack of satiety)

Which amino acids should be tested for deficiency in case of specific symptoms?

indication	Lead AS (mainly affected)
detoxification	cysteine, glutamic acid, glycine
hair loss	Cysteine, Methionine, Tyrosine, Glutathione
skin diseases	Arginine, cysteine, glutamine, lysine
heart disease	Arginine, Lysine, Methionine, Taurine, Carnitine
obesity	Arginine, Methionine, Phenylalanine, Tryptophan, Tyrosine
Gastrointestinal	Glutamine, Threonine, Methionine, Tryptophan, Glutathione
immune system	Lysine, methionine, arginine, tryptophan, glutamine
Parkinson's disease	Phenylalanine, Tyrosine, Carnitine

Source: Ganzimmun

Examples of amino acids in food

methionine	Egg, whey, whole grain bread, corn, rice
lysine	Meat, egg, whey, soy, potato, wheat germ, lentils
leucine	pumpkin seeds, oats, almonds, lentils, crispbread
isoleucine	Meat, cheese, pumpkin seeds, oats, almonds, lentils, soy
threonine	Meat, cheese, pumpkin seeds, oats, almonds, lentils, soy
valine	Meat, cheese, pumpkin seeds, oats, almonds, lentils, soy
phenylalanine	Meat, cheese, pumpkin seeds, oats, almonds, lentils, soy
tryptophan	Cocoa powder, buckwheat, linseed, sesame, apricot kernels, pumpkin seeds, African black bean (Griffonia simplicifolia)
histidine	Meat, liver, trout, tuna, cheese, lentils, sunflower seeds, lupins, soybeans
arginine	Meat, fish, nuts, soy, wheat germ, brown rice, oats
taurine	meat, fish
glutamine	Meat, fish, soy, beans
Glycine	beef, liver, peanuts, oats
carnitine	Red meat, crab
alanine	Beef, pork, egg white, whey, whole corn, rice, soy, oats
tyrosine	Cocoa powder, buckwheat, linseed, sesame, apricot kernels, pumpkin seeds

Examples of foods high in essential amino acids (and arginine)

Groceries (Specification in g AS per 100 g of food)	histidine	isoleucine *	Leucine *	lysine	methionine	phenylalanine	threonine	tryptophan	Valine *	arginine
Amaranth	0.38	0.58	0.87	0.74	0.22	0.54	0.55	0.18	0.67	1.06
bush beans (raw)	0.29	0.24	0.50	0.62	0.09	0.68	0.23	0.03	0.29	0.39
oats (raw)	0.20	0.41	0.77	0.44	0.16	0.53	0.37	0.16	0.57	0.68
hazelnut	0.40	0.57	1.10	0.47	0.21	0.71	0.48	0.21	0.75	2.27
sunflower seeds	0.69	1.13	1.70	0.99	0.56	1.28	0.95	0.37	1.33	2.46
lentils (raw)	0.59	1.11	1.78	1.73	0.19	1.23	0.98	0.22	1.33	1.95
lupins	1.03	1.61	2.74	1.93	0.25	1.43	1.33	0.28	1.51	3.87
almond sweet	0.53	0.91	1.51	0.60	0.27	1.20	0.63	0.17	1.18	2.84
soybeans (ripe, raw)	1.09	1.97	3.30	2.70	0.54	2.12	1.76	0.59	2.02	3.15
Tempeh (fermented soy)	0.48	0.91	1.47	1.06	0.23	0.89	0.68	0.17	0.89	1.12
tofu	0.40	0.74	1.24	0.96	0.19	0.84	0.57	0.20	0.76	1.14
egg	0.26	0.73	0.99	0.70	0.35	0.63	0.56	0.18	0.88	0.70
Parmesan	0.92	1.78	2.89	2.18	0.71	1.41	1.26	0.40	1.94	1.01
yogurt 1.5%	0.09	0.22	0.38	0.28	0.09	0.19	0.16	0.04	0.27	0.13
tuna (cooked)	0.88	0.98	1.75	1.79	0.49	0.85	0.95	0.24	1.15	1.01
beef (boiled)	0.49	0.75	1.22	1.27	0.37	0.62	0.67	0.16	0.82	0.91
Recommendation/day (in g)	0.7	1.4	2.7	2.1	0.7	1.75**	1.0	0.28	1.8	1.5

diagnostics "essential amino acids"

substance	Normal values ​​(mg/dl)	focal points
histidine	1,226-1,877	hemoglobin formation, detoxification, precursor of histamine
lysine	2,266-4,020	Cardiovascular protective factor, immune system, building block of carnitine
threonine	1,429-2,239	collagen building block, immune system, intestinal barrier
phenylalanine	0.760-2.973	Has an analgesic effect, precursor of tyrosine, thyroxine and catecholamines
tryptophan	0.694-1.838	Blood pressure reduction, sleep promotion, immune system, precursor kynurenine, vitamin B3, serotonin and melatonin
(arginine)	1,307-2,439	immune system, collagen synthesis, precursor of NO (e.g.B. vascular dilatation, redox system)
methionine	0.373-0.731	Methyl group donor, detoxification, immune system, redox system, precursor of cysteine ​​and taurine, building block of carnitine
leucine isoleucine valine	1,377-2,637 0.708-1.377 2,226-4,100	reserve energy nitrogen suppliers protein building blocks

Suggestions for the approximate daily requirement of essential amino acids (in g)

substance	Requirement
isoleucine (VK) Leucine (VK) lysine methionine (SH) phenylalanine (AAS) threonine tryptophan (AAS) Valine (VK) histidine (AAS) arginine (SE)	1.4 g 2.2 g 1.6 g 2.2 g 2.2 g 1 g 0.5 g 1.6 g 0.5 g 1.5 g

VK = Branched-chain amino acids; SH = Sulfur-containing amino acids; AAS = Aromatic amino acids; SE = semi-essential