Protein and Amino Acid Metabolism

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Protein and Amino Acid Metabolism

• Chapter 8

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Introduction - (FYI)

• Energy plus building
• Made up of amino acids
• Fuel source
• Alanine, leucine, glutamine

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Intro - Structure

• Nonessential (12)
• Essential (9)
• Peptide (-NH3)
• Peptide bonds
• Large number of different structures
• Most proteins contain up to 300 amino acids

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Intro - Animal versus Plant

• Animal protein is complete and more protein per
  gram
• Plant protein is incomplete and less protein per
  gram
• For example
• 2 ounces of fish 14 g of protein
• 2 ounces of macaroni 2 grams
• 2 ounces of beans 5 grams
• Soy the only complete plant source

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Intro - How Much Protein?

• Minimum 0.57 grams per kilogram of body weight
• RDA for egg whites 0.34 g/kg
• RDA 0.8 g/kg
• RDA 0.36 grams per pound
• 10 percent of total caloric intake

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Intro- Proteins in the diet

• Most of digestion occurs in the small
  intestine/gut
• Absorption into blood
• Joins the amino acid pool

• Functions of proteins
• Structure
• Transport
• Enzymes
• Hormones
• Immune
• Acid-base
• Fluid balance
• Energy
• Movement

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Amino Acid Pool

• Figure 8-3
• Blood, liver and skeletal muscle
• Equilibrium with blood
• Movement of amino acids from one site to another
  is very rapid
• Low or inadequate amino acids in one site can be
  compensated with amino acids from another site.
• Constant catabolism
• Half life of amino acids is a few days to a few
  months.

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Amino Acid Pool
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Nitrogen Balance

• An term used to indicate the balance in amino
  acids that are added to the body to those that
  are removed.
• Positive balance indicates more amino acids are
  staying in the body than are being removed.
• e.g. muscle hypertrophy.
• Negative balance indicates more amino acids are
  being removed than added.
• e.g. muscle atrophy.

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Nitrogen Balance
Fasting/Atrophy
Hypertrophy
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Protein Requirements

• Nitrogen balance can be maintained with 0.57 g /
  kg of protein intake
• Allowing for some error, the RDA for protein is
  set at 0.8 g/kg
• A positive nitrogen balance depends on having
  both adequate protein and energy (calories) in
  the diet.
• What is the best energy source for protein
  synthesis?
• Protein? Fat? Carbohydrate?

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Transamination

• Figure 8-5, 8-6 and Equations 8-2, 8-3.
• Transferring nitrogen from one amino acid to
  another
• Examples
• Alanine ? ketogluterate ? glutamate pyruvate
• Aspartate ? ketogluterate ? glutamate
  oxaloacetate

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Protein Metabolism

• Protein provides only 5-10 of energy
  requirements during exercise.
• Krebs cycle substrates
• Gluconeogenesis via the glucose-alanine cycle
• Muscle hypertrophy (branch chain amino acids)

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Amino acid carbon skeletons

• Figure 8-7
• Krebs cycle is imperfect
• Amino acids provide missing elements

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Glucose-Alanine Cycle
?
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Ammonia (NH4)

• Released during exercise
• Accumulation of ammonia may contribute to fatigue
  and ultimately become toxic
• ?-ketogluterate ammonia ? glutamate another
  ammonia ? glutamine
• Glutamine can be converted to glucose by the
  kidneys when the ammonia is removed

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Amino Acids and Muscle Growth

• Branch Chain Amino Acids Leucine, Isoleucine,
  and Valine
• Located mainly in skeletal muscle
• Nitrogen used for protein synthesis
• Carbons used for energy
• 20 of amino acids released from skeletal muscle
  are BBAA
• However, skeletal muscle contains all amino acids
• What does this mean in regard to protein
  supplements? Are certain amino acids more
  beneficial than others?

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Speculation on Other Amino Acids (FYI)

• Arginine, Lysine and Ornithine hGH
• Trypophan increase serotonin (decrease pain
  perception)
• BCAA block typrophan and serotonin production
  (delay fatigue)
• Glutamine remove ammonia
• Aspartates enhance fat metabolism
• Glycine formation of creatine

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Do athletes need more protein?

• Maybe.
• Resistance training
• 1.2-2.0 g per kg per day
• 15 of total calories
• Endurance training
• 1.2-1.4 g per kg per day
• How much protein are they already consuming?

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• NUTRITIONAL SUPPLEMENTS FOR WEIGHT GAIN
• SSE68- Volume 11 (1998), Number 1
• Priscilla M. Clarkson, Ph.D.
• Arginine, ornithine, histidine, lysine,
  methionine, and phenylalanine are purported to
  have anabolic effects. Two studies reported that
  ingestion of arginine and ornithine in
  conjunction with strength training significantly
  increased body mass and decreased body fat
  compared to a placebo (Elam, 1988 Elam et al.,
  1989). However, body composition was only
  estimated from skinfold measures, and diet was
  not controlled.
• It is claimed that these amino acids stimulate a
  release of growth hormone and insulin, and
  thereby increase muscle mass (Jacobson, 1990
  Kreider et al., 1993).
• Manufacturer-recommended doses of amino acid
  supplements are not likely to increase growth
  hormone and alter body weight. Commercially
  available supplements contain less than 4 g per
  serving higher levels of amino acids can cause
  mild-to-severe stomach cramps and diarrhea. These
  supplements are costly, and the consequences of
  using selected amino acids for a long period of
  time have not been determined. High amounts of
  one amino acid may affect the body's absorption
  of other amino acids. There is little reason at
  this time to believe that amino-acid supplements
  will promote gains in muscle mass.

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Do athletes need certain amino acids more than
others?

• PROTEIN POWER OR PUFFERY?
• Jeffrey J. Zachwieja, PhDSenior Scientist,
  Gatorade Sports Science Institute
• Digestion of dietary protein yields amino acids,
  which, after being absorbed, are available for
  metabolism and the growth and repair of all
  tissues in the body.
• Because many athletes are purposefully trying to
  add more muscle, most believe the protein content
  of the diet should be considerably higher than
  that of non-athletes.
• It is true that on average, athletes require
  slightly more protein (1.2-1.5 g/kg body weight
  0.5-0.7 grams/lb) than do less-active people
  (0.8-1.0 g/kg body weight 0.4-0.5 grams/lb).
• However, it is far from true that in order to
  meet this additional need, athletes must rely
  upon protein and amino acid supplements.
• Further, there is simply no scientific evidence
  to support the idea that the protein or amino
  acids in supplements are more effective for
  athletes than protein in ordinary foods.

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Do athletes need more protein during recovery
from exercise?

• Exercise is catabolic.
• Protein is needed for muscle repair, etc

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DIETARY PROTEIN, AMINO ACID SUPPLEMENTS, AND
RECOVERY FROM EXERCISEMartin J. Gibala, Ph.D.
GSSI

• The maximum daily protein requirement for
  endurance- or resistance-trained athletes is
  1.2-1.7 g per kg body weight (0.55-0.77 g/lb).
  This requirement can easily be met through diet
  alonewithout the use of supplementsprovided
  that sound nutrition principles are followed and
  energy intake is sufficient to maintain body
  weight.
• Amino acids are always a minor source of fuel,
  usually accounting for less than 5 of total
  energy expenditure.
• If enough carbohydrate is ingested, i.e., 1.2
  gkg-1h-1 (0.55 glb-1h-1) in 15-30 min
  intervals during the first 2-5 h of recovery,
  protein supplementation does not further increase
  muscle glycogen replenishment. However, if no
  food or too little carbohydrate is consumed,
  ingestion of protein or specific amino acids
  during recovery from prolonged exercise may
  accelerate glycogen resynthesis.
• Ingesting a single drink containing 0.1 g/kg of
  essential amino acids during the first few hours
  of recovery from heavy resistance exercise will
  produce a transient, net positive increase in
  muscle protein balance. It is uncertain if
  ingesting amino acids immediately before exercise
  or ingesting carbohydrate along with amino acids,
  either immediately before exercise or during
  recovery, further enhances the rate of muscle
  protein buildup during recovery.
• Ingesting several doses of essential amino acids
  during recovery will promote a net "anabolic"
  environment over 24 h, but it remains to be
  determined if the acute effects of
  supplementation eventually lead to greater gains
  in muscle mass following habitual training.

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Postexercise protein intake enhances whole-body
and leg protein accretion in humans DEANNA K.
LEVENHAGEN CHRISTOPHER CARR MICHAEL G. CARLSON
DAVID J. MARON MYFANWY J. BOREL PAUL J.
FLAKOLL Departments of Surgery, Biochemistry and
Medicine, Vanderbilt University Medical Center,
Nashville, TN MEDICINE SCIENCE IN SPORTS
EXERCISE 200234828-837 ABSTRACT LEVENHAGEN, D.
K., C. CARR, M. G. CARLSON, D. J. MARON, M. J.
BOREL, and P. J. FLAKOLL. Postexercise protein
intake enhances whole-body and leg protein
accretion in humans. Med. Sci. Sports Exerc.,
Vol. 34, No. 5, pp. 828-837, 2002. Purpose
Exercise increases the use of amino acids for
glucose production and stimulates the oxidation
of amino acids and other substrates to provide
ATP for muscular contraction, and thus the
availability of amino acids and energy for
postexercise muscle protein synthesis may be
limiting. The purpose of this study was to
determine the potential of postexercise nutrient
intake to enhance the recovery of whole-body and
skeletal muscle protein homeostasis in humans.
Methods Primed-continuous infusions of
L-1-13Cleucine and L-ring-2H5phenylalanine
were initiated in the antecubital vein and blood
was sampled from a femoral vein and a heated
(arterialized) hand vein. Each study consisted of
a 30-min basal, a 60-min exercise (bicycle at 60
O2max), and a 180-min recovery period. Five men
and five women were studied three times with an
oral supplement administered immediately
following exercise in random order NO 0, 0, 0
SUPP 0, 8, 3 or SUPPPRO 10, 8, 3 g of
protein, carbohydrate, and lipid, respectively.
Results Compared to NO, SUPP did not alter leg
or whole-body protein homeostasis during the
recovery period. In contrast, SUPPPRO increased
plasma essential amino acids 33, leg fractional
extraction of phenylalanine 4-fold, leg uptake of
glucose 3.5-fold, and leg and whole-body protein
synthesis 6-fold and 15, respectively. Whereas
postexercise intake of either NO or SUPP resulted
in a net leg release of essential amino acids and
net loss of whole-body and leg protein, SUPPPRO
resulted in a net leg uptake of essential amino
acids and net whole-body and leg protein gain.
Conclusions These findings suggest that the
availability of amino acids is more important
than the availability of energy for postexercise
repair and synthesis of muscle proteins.
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Macronutrient intake and whole body protein
metabolism following resistance exercise Brian
D. ROY Jonathon R. FOWLES Robert HILL MARK A.
TARNOPOLSKY Departments of Kinesiology,
Pathology, and Medicine, McMaster University,
Hamilton, Ontario, MEDICINE SCIENCE IN SPORTS
EXERCISE 2000321412-1418 ROY, B. D., J. R.
FOWLES, R. HILL, and M A. TARNOPOLSKY.
Macronutrient intake and whole body protein
metabolism following resistance exercise. Med.
Sci. Sports Exerc., Vol. 32, No. 8, pp.
1412-1418, 2000. The provision of carbohydrate
(CHO) supplements following resistance exercise
attenuated muscle protein (PRO) degradation (Roy
et al. J. Appl. Physiol. 821882-1888, 1997). The
addition of PRO may have a synergistic effect
upon whole body protein balance by increasing
synthesis (Biolo et al. Am. J. Physiol.
273E122-E129, 1997). Purpose To determine if
the macronutrient composition of a postexercise
beverage would alter muscle anabolism and/or
catabolism following resistance exercise.
Methods We provided isoenergetic CHO (1
gkg-1) and CHO/PRO/FAT supplements and placebo
(PL) immediately (t 0 h) and 1 h (t 1 h)
following resistance exercise (9 exercises/3
sets/80 1 RM) to 10 young, healthy,
resistance-trained males. Whole body leucine
turnover was determined from L-1-13Cleucine
kinetics at 4 h postexercise. Results No
differences were observed for urinary
3-methylhistidine or urea nitrogen excretion
between the trials. Leucine flux was
significantly elevated at 4 h postexercise for
both CHO/PRO/FAT (177.59 12.68 molkg-1h-1)
and CHO (156.18 7.77 molkg-1h-1) versus PL
(126.32 10.51 molkg-1h-1) (P lt 0.01). Whole
body leucine oxidation was elevated at 4 h for
CHO/PRO/FAT (29.50 3.34 molkg-1h-1) versus
CHO (16.32 2.33 molkg-1h-1) (P lt 0.01) and
PL (21.29 2.54 molkg-1h-1) (P lt 0.05).
Nonoxidative leucine disposal (NOLD) was
significantly elevated at 4 h for both
CHO/PRO/FAT (148.09 10.37 molkg-1h-1) and
CHO (139.86 7.02 molkg-1h-1) versus PL
(105.03 8.97 molkg-1h-1) (P lt 0.01).
Conclusions These results suggest that
consumption of either CHO or CHO/PRO/FAT
immediately and 1 h following a resistance
training bout increased NOLD as compared with a
placebo.
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Anabolic Processes During Recovery

• Protein during post-exercise may aid in muscle
  recovery/repair.
• Carbohydrate alone may be just as effective.
• If helpful, only 0.1 g/kg of protein every 1-2
  hours is needed.
• The type of protein seems to not influence
  protein synthesis
• Good sources are milk, tuna, peanut butter, etc.

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Key Topics

• Protein intake
• Amino acid pool
• Transamination
• Function of proteins related to exercise