leucine

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leucine

 [loo´sēn]
a naturally occurring amino acid, one of the essential amino acids, necessary for growth in infants and for nitrogen equilibrium in adults.

leu·cine (Leu, L),

(lū'sēn),
2-Amino-4-methylvaleric acid; the l-isomer is one of the amino acids found in proteins; a nutritionally essential amino acid.

leucine

/leu·cine/ (Leu) (L) (loo´sēn) an essential amino acid necessary for optimal growth in infants and for nitrogen equilibrium in adults.

leucine

(lo͞o′sēn′)
n.
An essential amino acid, C6H13NO2, obtained by the hydrolysis of protein by pancreatic enzymes during digestion and necessary for optimal growth in children and for the maintenance of nitrogen balance in adults.

leucine (Leu)

[lo̅o̅′sēn]
Etymology: Gk, leukos, white
a white crystalline essential amino acid required for optimal growth in infants and nitrogen equilibrium in adults. It cannot be synthesized by the body and is obtained by the hydrolysis of food protein during digestion. An inherited defect in one of the enzymes involved in the process results in a rare disorder called maple syrup urine disease. See also amino acid, leucinosis, maple syrup urine disease.
enlarge picture
Chemical structure of leucine

leu·cine

(lū'sīn)
The l-isomer is one of the amino acids of proteins; a nutritionally essential amino acid.

leucine

One of the essential AMINO ACIDS.
Leucineclick for a larger image
Fig. 209 Leucine . Molecular structure.

leucine (L, Leu)

one of 20 amino acids common in proteins. It has a NONPOLAR ‘R’ structure and is relatively insoluble in water. See Fig. 209 . The ISOELECTRIC POINT of leucine is 6.0.

amino acids

organic acids in which one or more of the hydrogen atoms is replaced by the amino group, NH2. They are the end-products of digestion of dietary protein and from them the body synthesizes its own proteins. Within the body amino acids also act as precursors of many other molecules essential for life. Amino acids may be categorized as essential or non-essential. essential amino acids: those that must be provided in the diet since the human body does not have the enzymes for their synthesis; of the 20 amino acids that are present in proteins or as free amino acids in the body, nine are 'essential' (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine). Of these, three are known as branched-chain aminoacids (BCAA): leucine is oxidized to a significant extent during exercise, and tracer studies that follow leucine kinetics are often used as an estimation of protein turnover; isoleucine and valine can also serve as fuel sources. It has been claimed that ingestion of BCAA before and during exercise may improve the physiological and psychological responses, and that BCAA with arginine and/or other amino acids may promote growth hormone release, but other studies do not support this. There are no known toxic effects. See also ergogenic aids, gluconeogenesis; Table 1.
Table 1: Ergogenic aids: supplements used by athletes
SubstanceDescriptionClaimed ergogenic effectSupporting evidence
With clear scientific evidence
CaffeineStimulant in coffee and tea
  • Benefits performance by improving alertness, concentration, reaction time.
  • Increases fat oxidation during endurance exercise.
Improves performance in most events, except very short high-intensity exercise; increases cognitive functioning during exercise.
CreatineCarrier of high-energy phosphates in muscleIncreases the energy reserve, improves strength, reduces fatigue, and increases protein synthesisIncreases intramuscular Cr and PCr; improves performance in repeated sprint bouts (and reported to do so after even a single bout); improves recovery between bouts (but response varies between individuals). Anabolic properties unclear.
  • Sodium bicarbonate
  • Sodium citrate
BuffersImproves high-intensity exercise performance by limiting decrease in pH in ECF as a whole and indirectly in muscle ICFLarge doses can improve performance
With mixed scientific evidence
Antioxidant nutrientsVitamins, especially C and EProvides protection against muscle damage by reducing oxidative stressBenefits established at cellular level; no detectable aid to performance
ArginineAmino acid in normal dietStimulates release of growth hormone, promoting gain in muscle mass and strengthSome evidence of GH promotion when combined with other amino acids (ornithine, lysine, BCAA); no conclusive evidence of effect when taken alone
Branched-chain amino acids (BCAA)Leucine, isoleucine and valine
  • Retards the development of central fatigue and so improves performance.
  • Improves efficiency of training
No good evidence of improved endurance performance. Evidence of accelerated recovery from muscle fatigue when given with other amino acids during eccentric exercise training
GlutamineAmide of amino acid glutamateMaintains a healthy immune system during training and improves muscle glycogen resynthesisDoes not affect immune function; possibly affects muscle glycogen resynthesis
GlycerolComponent of triacylglycerol moleculeInduces hyperhydration, decreases heat stress, and improves performanceDoes have the first two actions, but effects on performance are unclear
Lacking scientific support
AndrostenedioneSynthetic productIncreases testosterone and thus muscle mass and strength, and improves recoveryDoes not increase testosterone secretion; has no effect on strength
Hydroxy-methyl butyrate (HMB)Metabolite of the amino acid leucineEnhances gain in body mass and strength associated with resistance training, and improves recoveryPossible small effects only on lean body mass and strength
BoronMicronutrient present in vegetables and non-citrus fruitsIncreases testosterone levels, to improve bone density, muscle mass, and strengthImproves bone mineral density in postmenopausal women; no effect on bone density, muscle mass or strength in men
CarnitineSubstance important for fatty acid transport into mitochondriaImproves fat oxidation, helps weight lossNo supporting evidence
CholinePrecursor of acetylcholineImproves performance, decreases fatigue and enhances fat metabolismNo supporting evidence
Chromium (chromium picolinate)Micronutrient that potentiates insulin actionPromotes fat oxidation and muscle buildingNo supporting evidence
Coenzyme Q10Part of the electron transport chain in the mitochondriaImproves aerobic capacity and cardiovascular dynamicsNo supporting evidence
GinsengRoot of the Araliaceous plantImproves strength, performance, stamina, and cognitive functioning; reduces fatigueNo supporting evidence
InosineNucleoside found naturally in brewer's yeast and organ meatsIncreases ATP stores, improve strength, training quality, and performanceNo supporting evidence
Medium-chain triacylglycerols (MCT)Triglycerides containing fatty acids with a carbon chain length of 6-10Improves energy supply, reduces rate of muscle glycogen breakdown, and improves performanceNo supporting evidence
PyruvateEnd-product of aerobic glycolysisImproves endurance capacity and recovery; increases glycogen storageLimited supporting evidence
PolylactatePolymer of lactateProvides energyNo effects on performance
Wheat germ oilWheat embryo extractImproves enduranceNo supporting evidence

leu·cine

(lū'sīn)
The l-isomer is one of the amino acids of proteins; a nutritionally essential amino acid.

leucine

(loo´sēn),
n one of the essential amino acids. See also amino acid.

leucine

Leu; a naturally occurring amino acid, essential for growth in the young and for nitrogen equilibrium in adults.

leucine aminopeptidase
a digestive enzyme of small intestine enterocytes (brush border).
DL-leucine
synthetic form of leucine.
leucine enkephalin
leu-enkephalin; see enkephalin.
L-leucine
natural form of leucine.
leucine zipper
a structured motif found in some DNA binding regulatory proteins formed from a region of α-helix containing at least four leucines, each separated by six amino acids from one another; the leucines align along one edge of the α-helix with one leucine at every second turn of the helix such that the leucine of one protein can interdigitate with the leucines of another protein in a zipper manner.
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