Protein metabolism

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Protein metabolism

  1. 1. Dr.Mahr-un -nisa Proteins
  2. 2. Proteins-----AA  Proteins are made from 20 different amino acids, 9 of which are essential.  Each amino acid has an amino group, an acid group, a hydrogen atom, and a side group.  It is the side group that makes each amino acid unique.  The sequence of amino acids in each protein determines its unique shape and function.
  3. 3.  Amino Acids  Have unique side groups that result in differences in the size, shape and electrical charge of an amino acid  Nonessential amino acids, also called dispensable amino acids, are ones the body can create.  Nonessential amino acids include alanine, arginine, asparagines, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.
  4. 4.  Amino Acids  Essential amino acids, also called indispensable amino acids, must be supplied by the foods people consume.  Essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenyalanine, threonine, tryptophan, and valine.  Conditionally essential amino acids refer to amino acids that are normally nonessential but essential under certain conditions.
  5. 5. Amino Acid Requirements of Humans -------------------------------------------------------------------- Nutritionally Essential Nutritionally Nonessential -------------------------------------------------------------------- Argininea Alanine Histidine Asparagine Isoleucine Aspartate Leucine Cysteine Lysine Glutamate Methionine Glutamine Phenylalanine Glycine Threonine Proline Tryptophan Serine Valine Tyrosine --------------------------------------------------------------------- a “ Nutritionally semiessential.” Synthesized at rates inadequate to support growth of children.
  6. 6. What is protein  Proteins  Amino acid chains are linked by peptide bonds in condensation reactions.  Dipeptides have two amino acids bonded together.  Tripeptides have three amino acids bonded together.  Polypeptides have more than two amino acids bonded together.  Amino acid sequences are all different, which allows for a wide variety of possible sequences.
  7. 7. M. Zaharna Clini. Chem. 2009 Peptide bond
  8. 8. The Chemist’s View of Proteins  Proteins  Protein Shapes  Hydrophilic side groups are attracted to water.  Hydrophobic side groups repel water.  Coiled and twisted chains help to provide stability.
  9. 9. M. Zaharna Clini. Chem. 2009 Classification of protein  Proteins are polymers of amino acids produced by living cells in all forms of life.  A large number of proteins exist with diverse functions, sizes, shapes and structures but each is composed of essential and non-essential amino acids in varying numbers and sequences.  The number of distinct proteins within one cell is estimated at 3,000 - 5,000  The most abundant organic molecule in cells (50-70% of cell dry weight)
  10. 10. M. Zaharna Clini. Chem. 2009 Size  A typical protein contains 200-300 amino acids, but some are much smaller and some are much larger  Proteins range in molecular weight from 6,000 Daltons (insulin) to millions of Daltons (structural proteins)
  11. 11. M. Zaharna Clini. Chem. 2009 Protein Structure  Primary structure – sequence of AA  In order to function properly, proteins must have the correct sequence of amino acids.  e.g when valine is substituted for glutamic acid in the β chain of HbA, HbS is formed, which results in sickle-cell anemia.
  12. 12. M. Zaharna Clini. Chem. 2009 Secondary structure  Initial helical folding  Beta pleated sheet  Held together by Hydrogen bonding
  13. 13. M. Zaharna Clini. Chem. 2009 Tertiary Structure  Chain folds back on itself to form 3D structure  Interaction of R groups  Responsible for biologic activity of molecule
  14. 14. M. Zaharna Clini. Chem. 2009 Quaternary structure  2 or more polypeptide chains binding together  eg. Hemoglobin  Hemoglobin has 4 subunits  Two α chains  Two β chains  Many enzymes have quaternary structures
  15. 15. M. Zaharna Clini. Chem. 2009 Classification by Protein Structure  Simple Proteins (contain only amino acids) are classified by shape as –  Globular proteins: compact, tightly folded and coiled chains  Majority of serum proteins are globular  Fibrous proteins: elongated, high viscosity (hair, collagen)
  16. 16. M. Zaharna Clini. Chem. 2009 Classification by Protein Structure  Conjugated proteins contain non-amino acid groups  Amino acid portion is called apoprotein and non-amino acid portion is called the prosthetic group  It is the prothetic groups that define the characteristics of these proteins.  Name of the conjugated protein is derived from the prosthetic group
  17. 17. M. Zaharna Clini. Chem. 2009 Conjugated Proteins Classification Prosthetic group Example Lipoprotein Lipid HDL Glycoprotein Carbohydrates Immunoglo- bulins Phosphoprotein Phosphate Casein of milk
  18. 18. M. Zaharna Clini. Chem. 2009 Functions of proteins  Generally speaking, proteins do everything in the living cells  Functional classification of plasma proteins is useful in understanding the changes that occur in disease:  Tissue nutrition  Proteins of immune defense  Antibodies  Acute phase proteins  Proteins associated with inflammation  Transport proteins( albumin, transferrin)  Proteins used to bind and transport  Hemostasis  Proteins involved in forming clots and acting very closely with complement
  19. 19. M. Zaharna Clini. Chem. 2009 Functions of proteins  Regulatory  ( receptors, hormones )  Catalysis,  enzymes  Osmotic force  Maintenance of water distribution between cells and tissue and the vascular system of the body  Acid-base balance  Participation as buffers to maintain pH  Structural, contractile, fibrous and keratinous
  20. 20. Monogastric Protein Digestion  Whole proteins are not absorbed  Too large to pass through cell membranes intact  Digestive enzymes  Hydrolyze peptide bonds  Secreted as inactive pre-enzymes  Prevents self-digestion H3N+ C H C R O N H C H C O R N H C H C R O O–
  21. 21. Monogastric Protein Digestion  Initiated in stomach  HCl from parietal cells  Stomach pH 1.6 to 3.2  Denatures 40 , 30 , and 20 structures  Pepsinogen from chief cells  Cleaves at phenylalanine, tyrosine, tryptophan  Protein leaves stomach as mix of insoluble protein, soluble protein, peptides and amino acids Aromatic amino acids Pepsinogen HCl Pepsin
  22. 22. Protein Digestion – Small Intestine  Pancreatic enzymes secreted  Trypsinogen  Chymotrypsinogen  Procarboxypeptidase  Proelastase  Collagenase Zymogens
  23. 23. Monogastric Digestion – Small Intestine  Zymogens must be converted to active form  Trypsinogen Trypsin  Endopeptidase  Cleaves on carbonyl side of Lys & Arg  Chymotrypsinogen Chymotrypsin  Endopeptidase  Cleaves carboxy terminal Phe, Tyr and Trp  Procarboxypeptidase Carboxypeptidase  Exopeptidase  Removes carboxy terminal residues Enteropeptidase/Trypsin Trypsin Trypsin
  24. 24. Protein Digestion  Small intestine (brush border)  Aminopeptidases  Cleave at N-terminal AA  Dipeptidases  Cleave dipeptides  Enterokinase (or enteropeptidase)  Trypsinogen → trypsin  Trypsin then activates all the other enzymes
  25. 25. Trypsin Inhibitors  Small proteins or peptides  Present in plants, organs, and fluids  Soybeans, peas, beans, wheat  Pancreas, colostrum  Block digestion of specific proteins  Inactivated by heat
  26. 26. Protein Digestion  Proteins are broken down to  Tripeptides  Dipeptides  Free amino acids
  27. 27. Free Amino Acid Absorption  Free amino acids  Carrier systems  Neutral AA  Basic AA  Acidic AA  Imino acids  Entrance of some AA is via active transport  Requires energy Na+ Na+
  28. 28. Peptide Absorption  Form in which the majority of protein is absorbed  More rapid than absorption of free amino acids  Active transport  Energy required  Metabolized into free amino acids in enterocyte  Only free amino acids absorbed into blood
  29. 29. Absorption of Intact Proteins  Newborns  First 24 hours after birth  Immunoglobulins  Passive immunity  Adults  Para cellular routes  Tight junctions between cells  Intracellular routes  Endocytosis  Pinocytosis  Of little nutritional significance...  Affects health (allergies and passive immunity)
  30. 30. Protein Transport in the Blood  Amino acids diffuse across the basolateral membrane  Enterocytes → portal blood → liver → tissues  Transported mostly as free amino acids  Liver  Breakdown of amino acids  Synthesis of non-essential amino acids
  31. 31. Groff & Gropper, 2000 Overview of Protein Digestion and Absorption in Monogastrics
  32. 32. OVERVIEW OF AMINO ACID METABOLISM ENVIRONMENT ORGANISM Ingested protein Bio- synthesis Protein AMINO ACIDS Nitrogen Carbon skeletons Urea Degradatio n (required) 1 2 3 a b Purines Pyrimidines Porphyrins c c Used for energy pyruvate α-ketoglutarate succinyl-CoA fumarate oxaloacetate acetoacetate acetyl CoA (glucogenic)(ketogenic)
  33. 33. Amino Acid Catabolism  Deamination of Amino Acids removal of the a-amino acids Oxidative Deamination Non-oxidative Deamination Transamination
  34. 34. TRANSAMINATION
  35. 35. The term amphibolic is used to describe a biochemical pathway that involves both catabolism and anabolism
  36. 36. Reductive amination catalyzed by glutamate dehydrogenase (this is physiological important becouse high conc. Of NH4 ion are cytotoxic)
  37. 37. Glutamine synthesis is coupled to hydrolysis of ATP
  38. 38. Pyruvate is an amphibolic intermediate in synthesis of alanine
  39. 39. Glutamte dehydrogenase, glutamine synthetase and aminotranferases play central roles in amino acid biostynthsis  The combined action of the above said enzymes converts inorganic ammonium ion in to the α-amino nitrogen of AA
  40. 40. Asparagine synthesis is energetically favorable due to coupling to ATP hydrolysis
  41. 41. Serine biosynthesis(oxidation of the α-hydroxyl group of the glycolytic intermidiate 3-phosphoglycerate by 3- phosphoglycerate dehygrogenase convert it to 3- phosphohydroxypuruvate. Transamination and subsequent dephosphorylation is strongly favored)
  42. 42. Multistep pathway for glycine biosynthesis
  43. 43. Glycine is also synthesized from serine
  44. 44. Cysteine is not nutritionally essential, however it is derived from methionine +NH3 CH C H2 C O- O H2 C S CH3
  45. 45. Tyrosine is formed from phenylalanine
  46. 46. Hydroxyproline is formed after protein synthesis
  47. 47. Selenocysteine is synthesized from serine and selenophosphate
  48. 48. Amino acids that are synthesized de novo in humans. All are related by a small number of steps to glycolysis or TCA cycle intermediates.
  49. 49. Salvage pathways for formation of certain nonessential amino acids from other amino acids Amino Acid formed Precursor Amino Acid Arginine Proline Cysteine Methionine Tyrosine Phenylalanine
  50. 50. NITROGEN BALANCE Nitrogen balance = nitrogen ingested - nitrogen excreted (primarily as protein) (primarily as urea) Nitrogen balance = 0 (nitrogen equilibrium) protein synthesis = protein degradation Positive nitrogen balance protein synthesis > protein degradation Negative nitrogen balance protein synthesis < protein degradation
  51. 51. UREA CYCLE mitochondria cytosol Function: detoxification of ammonia (prevents hyperammonemia)
  52. 52. FATE OF THE CARBON SKELETONS Carbon skeletons are used for energy. Glucogenic: TCA cycle intermediates(gluconeogensis) Ketogenic: acetyl CoA, acetoacetyl CoA, or acetoacetate
  53. 53. Protein synthesis  On-going, semicontinuous activity in all cells but rate varies greatly between tissues
  54. 54. Rate of protein synthesis Ks (%/d) Tissue Pig Steer Liver Gut Muscle 23 45 5 21 39 2 Ks = fraction of tissue protein synthesized per day
  55. 55. Protein synthesis  On-going, semicontinuous activity in all cells but rate varies greatly between tissues  Rate is regulated by hormones and supply of amino acids and energy  Energetically expensive  requires about 5 ATP per one peptide bond  Accounts for about 20% of whole-body energy expenditure
  56. 56. Protein degradation  Also controlled by hormones and energy status  Method to assist in metabolic control  turns off enzymes
  57. 57. Protein synthesis and degradation  Synthesis must exceed degradation for net protein deposition or secretion  Changes in deposition can be achieved by different combinations of changes in synthesis and degradation
  58. 58. Changes in deposition Synthesis Degradation Deposition No change No change No change
  59. 59. Protein synthesis and degradation  Synthesis must exceed degradation for net protein deposition or secretion  Changes in deposition can be achieved by different combinations of changes in synthesis and degradation  Allows for fine control of protein deposition
  60. 60. Proline biosynthesis(the initial reaction of proline biosynthsis converts the ᵞ-carboxyl group of glutamate to the mixed acid anhydride of glutamate ᵞ-phospate. Subsequent reduction form glutamate ᵞ- semialdehyde,, which following spontaneously cyclization is reduced to L-Proline )
  61. 61. Protein synthesis and degradation  Other possible reasons for evolution of protein turnover include  Allows post-translational conversion of inactive peptides to active forms (e.g., pepsinogen to pepsin)  Minimizes possible negative consequences of translation errors
  62. 62. Protein catabolism  Some net catabolism of body proteins occurs at all times  Expressed as urinary nitrogen excretion  yields urea  Minimal nitrogen excretion is termed endogenous urinary nitrogen (EUN)
  63. 63. Urinary nitrogen excretion Urine KIDNEY LIVER Urea Urea CO2 Amino acids keto acids NH3 Blood
  64. 64. Protein Synthesis
  65. 65. Protein Synthesis  Synthesis= the process of building or making  DNA= (deoxyribonucleic acid) the genetic code or instructions for the cell  RNA= ribonucleic acid  Amino Acids= building blocks of proteins
  66. 66. DNA RNA Deoxyribonucleic Acid Ribonucleic Acid Sugar=deoxyribose Sugar= ribose Contains 1 more H atom than deoxyribose Double stranded Single stranded- a single strand of nucleotides Nitrogen bases: ATCG Nitrogen bases: AUCG U=Uracil
  67. 67. http://www.princeton.ed u/ http://image s2.clinicalto ols.com/ima ges/gene/dn a_versus_rn a_reversed.j pg
  68. 68. STEP 1: TRANSCRIPTION= making RNA Location: Eukaryotes-nucleus Prokaryotes-cytoplasm  1. RNA polymerase binds to the gene’s promoter  2. The two DNA strands unwind and separate.  3. Complementary nucleotides are added using the base pairing rules EXCEPT:  A=U 
  69. 69. Try this example.  Using the following DNA sequence, what would be the complementary RNA sequence?  ATCCGTAATTATGGC  UAGGCAUUAAUACCG
  70. 70. http://www.odec.ca/projects/2004/mcgo4s0/public_html/t3/mRNA%20to%20protein.gif
  71. 71.  1. Messenger RNA= mRNA is a form of RNA that carries the instructions for making the protein from a gene and delivers it to the site of translation.  Codon= three nucleotide sequence  Transfer RNA= tRNA single strands of RNA that temporarily carry a specific amino acid on one end and has an anticodon  Anticodon-a 3 nucleotide sequence that is complementary to an mRNA codon  Ribosomal RNA= rRNA- a part of the structure of ribosomes
  72. 72. Codon and Anticodon  Codon-found on mRNA Anticodon-found on tRNA http://images.google.com/imgres? imgurl=http://www.obgynacademy.com/basicsciences/feto logy/genetics/images/codon_GCA.gif&imgrefurl=http://ww w.obgynacademy.com/basicsciences/fetology/genetics/&u sg=__4MvAO2N3sXbERXQwODVDSqtsOjM=&h=160&w= 168&sz=4&hl=en&start=5&tbnid=toyuIN8drVBr4M:&tbnh= 94&tbnw=99&prev=/images%3Fq%3Dcodon%26gbv %3D2%26hl%3Den http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleim ages/kaiser/tRNA_arg.jpg
  73. 73. STEP 2-TRANSLATION- Assembling proteins- in the cytoplasm  mRNA leaves nucleus and enters cytoplasm  tRNA molecules with the complementary anticodon and a specific amino acid arrives at the ribosome where the mRNA is waiting.  Peptide bond forms between amino acids  tRNA molecule leaves and a new one comes with another amino acid.  Amino acids continue to attach together until the stop codon and a protein is formed
  74. 74. SUMMARY  Transcription= process of making RNA from DNA  Translation= RNA directions are used to make a protein from amino acids • DNA→RNA →Protein  Transcription Translation nucleus Cytoplasm on ribosome
  75. 75. DNA RNA Deoxyribonucleic Acid Ribonucleic Acid Sugar=deoxyribose Sugar= ribose Contains 1 more H atom than deoxyribose Double stranded Single stranded- a single strand of nucleotides Nitrogen bases: ATCG Nitrogen bases: AUCG U=Uracil
  76. 76. Video Clips  http://www.youtube.com/watch?v=KvYEqG  http://www.youtube.com/watch?v=B6O6uR
  77. 77. DNA Replication RNA Transcription DNA polymerase is used. RNA polymerase is used. DNA nucleotides are linked. RNA nucleotides are linked. A DNA molecule is made. An RNA molecule is made. Both DNA strands serve as templates. Only one part of one strand of DNA ( a gene) is used as a template.
  78. 78. Explain the steps in protein synthesis. http://stemcells.nih.gov /info/scireport/images/f igurea6.jpg
  79. 79. Ruminant Protein Digestion  Ruminants can exist with limited dietary protein sources due to microbial protein synthesis  Essential amino acids synthesized  Microbial protein is not sufficient during:  Rapid growth  High production
  80. 80. Protein in the Ruminant Diet  Types of protein:  Dietary protein – contains amino acids  Rumen Degradable Protein (RDP) – available for use by rumen microbes  Rumen Undegradable Protein (RUP) – escapes rumen fermentation; enters small intestine unaltered  Varies with diet, feed processing  Dietary non-protein nitrogen (NPN) – not true protein; provides a source of nitrogen for microbial protein synthesis  Relatively CHEAP - decreases cost of protein supplementation
  81. 81. Ruminant Protein Feeding  Feed the rumen microbes first (RDP)  Two counteractive processes in rumen  Degradation of (dietary) protein  Synthesis of microbial protein  Feed proteins that will escape fermentation to meet remainder of animal’s protein requirements  Escape protein, bypass protein, or rumen undegradable protein (RUP)  Aldehydes increase inter-protein cross-linking  Heat treatment  Utilization depends on  Digestibility of RUP source in the small intestine  Protein quality
  82. 82. Protein Degradation in Rumen Feedstuff % Degraded in 2 hours Urea 100 Alfalfa (fresh) 90 Wheat Grain 78 Soybean Meal 65 Corn Grain 48 Blood Meal 18
  83. 83. Rumen Protein Utilization  Factors affecting ruminal degradation  Rate of passage  Rate of passage ↑ ⇒ degradation ↓  Solubility in water  Must be solubilized prior to degradation  Heat treatment  Degradation ↓  N (and S) availability  Energy availability (carbohydrates)
  84. 84. Protein Fractions  Dietary proteins classified based on solubility in the rumen  A  NPN, instantly solubilized/degraded  B1 B2 B3  Potentially degradable  C  Insoluble, recovered in ADF, undegradable
  85. 85. Ruminant Protein Digestion  Rumen microbes use dietary protein  Creates difference between protein quality in feed and protein actually absorbed by host  Microbes break down dietary protein to  Amino acids  NH3, VFAs, and CO2  Microbes re-synthesize amino acids  Including all the essential amino acids from NH3 and carbon skeletons No absorption of protein or amino acids from rumen (or from cecum or large intestine!)
  86. 86. Protein Hydrolysis by Rumen Microbes  Process with multiple steps  Insoluble protein is solubilized when possible  Peptide bonds of solubilized protein are cleaved  Microbial endo- and exo-peptidases  Amino acids and peptides released  Peptides and amino acids absorbed rapidly by bacteria  Bacteria degrade into ammonia N (NH3)  NH3 used to produce microbial crude protein (MCP)
  87. 87. Microbial Crude Protein (MCP)  Protein produced by microbial synthesis in the rumen  Primary source of protein to the ruminant animal  Microbes combine ammonia nitrogen and carbohydrate carbon skeleton to make microbial crude protein  Diet affects the amount of nitrogen entering the small intestine as microbial crude protein
  88. 88. Factors Limiting Microbial Protein Synthesis  Amount of energy  ATP  Available nitrogen  NPN  Degraded feed intake protein nitrogen (RDP)  Available carbohydrates  Carbon residues for backbone of new amino acid Microbial crude protein synthesis relies on synchronization of carbohydrate (for carbon backbones) and nitrogen availability (for amino group)
  89. 89. Microbial Protein Synthesis  Synchronization of carbohydrate and N availability  NPN supplementation  Carbohydrates used for carbon skeleton of amino acids VFA (CHO fermentation) Rumen NH3 Blood NH3 Adapted from Van Soest, 1994 Time post-feeding Concentration Carbon backbone (from CHO fermentation)
  90. 90. Microbial Protein Formation Dietary NPN Dietary Soluble RDP Microbial Proteins Amino Acids Carbon Skeletons Sulfur Other Co-factors NH3 ATP Dietary Starch Sugar Dietary Cellulose Hemicellulose rapid slow rapid slower Dietary Insoluble RDP very slow
  91. 91. Nitrogen Recycling  Excess NH3 is absorbed through the rumen wall to the blood  Quickly converted to urea in the liver  Excess NH3 may elevate blood pH  Ammonia toxicity  Costs energy  Urea (two ammonia molecules linked together)  Relatively non-toxic  Excreted in urine  Returned to rumen via saliva (rumination important)  Efficiency of nitrogen recycling decreases with increasing nitrogen intake
  92. 92. Nitrogen Recycling  Nitrogen is continually recycled to rumen for reutilization  Ability to survive on low nitrogen diets  Up to 90% of plasma urea CAN be recycled to rumen on low protein diet  Over 75% of plasma urea will be excreted on high protein diet  Plasma urea enters rumen  Saliva  Diffuses through rumen wall from blood Urea Ammonia + CO2 Urease
  93. 93. Feed Protein, NPN and CHO Feed Protein Feed NPN NH3/NH4 Bacterial N NH4 + loss MCP RDP RUP Feed Protein AA MCP AA NH3 Liver Blood Urea Salivary N ATP RUMEN SMALL INTESTINE
  94. 94. Ruminant Digestion and Absorption  Post-ruminal digestion and absorption closely resembles the processes of monogastric animals  However, amino acid profile entering small intestine different from dietary profile
  95. 95. Overview of Protein Feeding Issues in Ruminants  Rumen degradable protein (RDP)  Low protein quality in feed ⇒ very good quality microbial proteins  Great protein quality in feed ⇒ very good quality microbial proteins  Feed the cheapest RDP source that is practical regardless of quality  Rumen undegradable protein (RUP)  Not modified in rumen, so should be higher quality protein as fed to animal  May cost more initially, but may be worth cost if performance boosted enough
  96. 96. Salivary Urea NPN NH3 POOL Dietary Nitrogen Non-utilized Ammonia NH3 UREA LIVER LEVEL TO PROVIDE FOR MAXIMUM MICROBIAL GROWTH MICROBIAL PROTEIN 65% OF PROTEIN 35% OF PROTEIN SMALL INTESTINE AMINO ACIDS AMINO ACIDSPROTEIN AMINO ACIDS PEPTIDES Reticulo-rumen RUP RDP Recycled urea
  97. 97. Functional Feeds  Functional feeds may be defined as any feed or feed ingredient that produces a biological effect or health benefit that is above and beyond the nutritive value of that feedstuff  Many feeds and their components fit this definition
  98. 98. Functional Proteins  Functional proteins are feed-derived proteins that, in addition to their nutritional value, produce a biological effect in the body
  99. 99. Feedstuffs with Biologically Active Proteins  Milk  Colostrum  Whey Protein Concentrates/Isolates  Plasma or serum  Other animal-derived feedstuffs  Fish meal  Meat and bone meal  Fermented animal-based products  Yeast  Lactobacillus organisms  Soy products
  100. 100. Protein Size Affects Function  Many protein hormones are functional even when fed to animals  thyrotropin-releasing hormone (TRH, a 3-amino acid peptide)  luteinizing hormone-releasing hormone (LHRH, a 10-amino acid peptide)  insulin (a 51-amino acid polypeptide)  The smaller the peptide, the more “functional” it is when fed  100% activity for TRH, 50% for LHRH, and 30% for insulin  Feedstuffs containing protein hormones (colostrum) have biological activity when fed to animals
  101. 101. Production of Bioactive Peptides From Biologically-Inactive Proteins  Peptides produced from intact inactive proteins by incomplete digestion via proteases in stomach and duodenum or via microbial proteases in rumen  Many of these biologically active peptides (typically 2-4 amino acid residues) are stable from further digestion  Some peptides bind to specific epithelial receptors in intestinal lumen and induce physiological reactions  Some peptides are absorbed intact by a specific peptide transporter system into the circulatory system and transported to target organs
  102. 102. Responses to Feeding Functional Proteins or Peptides  Antimicrobial – including control of gut microflora  Antiviral  Binding of enterotoxins  Anti-carcinogenic  Immunomodulation  Anti-oxidant effects  Opioid effects  Enhance tissue development or function  Anti-inflammatory  Appetite regulation  Anti-hypertensive  Anti-thrombic
  103. 103. Functional Activity of Major Milk Proteins  Caseins (α, β and κ)  Transport of minerals and trace elements (Ca, PO4, Fe, Zn, Cu), precursor of bioactive peptides, immunomodulation (hydrolysates/peptides)  β-Lactoglobulin  Retinol carrier, binding fatty acids, potential antioxidant, precursor for bioactive peptides  α-Lactalbumin  Lactose synthesis in mammary gland, Ca carrier, immunomodulation, anticarcinogenic, precursor for bioactive peptides  Immunoglobulins  Specific immune protection (antibodies and complement system), G, M, A potential precursor for bioactive peptides  Glycomacropeptide  Antiviral, antithrombotic, bifidogenic, gastric regulation  Lactoferrin  Antimicrobial, antioxidative, anticarcinogenic, anti-inflammatory, immunomodulation, iron transport, cell growth regulation, precursor for bioactive peptides  Lactoperoxidase  Antimicrobial, synergistic effect with Igs and LF  Lysozyme  Antimicrobial, synergistic effect with Igs and LF  Serum albumin  Precursor for bioactive peptides  Proteose peptones  Potential mineral carrier
  104. 104. Functional Activity of Minor Milk Proteins  Growth factors (IgF, TGF, EGF)  stimulation of cell proliferation and differentation  Cytokines  regulation of immune system (interferons, interleukins, TGFβ, TNFα)  Inflammation  Increases immune response  Milk basic protein (MBP)  Promotion of bone formation and suppression of bone resorption  Osteopontin  Modulation of trophoblastic cell migration
  105. 105. Protein Fragments That Have Biological Activity
  106. 106. Functional Protein Effects During Toxin or Disease Challenge  During intestinal inflammation, some functional proteins:  Reduce  local inflammatory response  excessive activation of inflammatory cells  permeability  Increase  Nutrient absorption  Barrier function  Intestinal health  During intestinal inflammation, some functional proteins:  Are absorbed and create adverse allergenic and immune responses in the body Modified from Campbell, 2007

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