Protein Digestion Flashcards
Pancreatic Secretions
Endopeptidases secreted in a zymogen form:
trypsinogen, chymotrypsinogen and proelastase,
Trypsinogen
Forms trypsin which is specific for peptide bonds with basic amino acids
Chymotrypsinogen
Forms chymotrypsin which is specific for bonds involving non-charged aromatic amino acids.
Proelastase
Forms elastase which is a protease with broad specificity, including the capacity to digest elastin.
Endopeptidases
Hydrolyze peptide bonds within primary structure
Ex: Pepsin
Exopeptidases
Cleave AA off terminal end of molecule
Carboxypeptidases
Remove AA from carboxyl group end
Aminopeptidases
Act on terminal AA with free amino group
Digestion Non-ruminants
Denaturing of proteins exposes peptide bonds
Bonds are split through hydrolysis into component AA
Free AA are main absorbed compound; some small peptides
Digestive Process
Chief cells in gastric mucosa secrete pepsinogen and HCL formed in the lumen splits of protective polypeptide to form pepsin.
Pepsin
An endopeptidase, specific for peptide bonds between aromatic (e.g. tyrosine, phenylalanine) or dicarboxylic (e.g. glutamic acid, aspartic acid) amino acids.
Supplemental Acidifiers
(organic acids such as citric and fumaric acids) is sometimes used in diets for baby pigs, to avoid colonization of enteric pathogens when pH is decreased (3-5)
Rennin (chymosin)
Rennin in the presence of calcium causes casein to coagulate or clot. Formation of milk clots is necessary to keep the immature small intestine from being overloaded, as it reduces the rate at which milk protein exits the stomach into the small intestine.
*Protective role in prey to go hours without food when hiding
Major Site of Protein Digestion
Small Intestines
Pancreatic Enzyme Inhibitors
soybeans/legume seeds and nuts contain large protein molecules that combine irreversibly combine with trypsin & chymotrypsin.
Reduces digestibility; may cause AA deficiencies
Inactivate inhibitors
Heat treatment
Intestinal Vili Secretions
Aminopeptidases & carboxypeptidases complete protein digestion in the brush border. This liberates free amino acids for absorption
Amino Acid Absorption
Attach to carrier protein coupled to a sodium-potassium pump (Active transport) into cell. Dipeptides & tripeptides must be hydrolyzed to free AA intracellularly
Food Allergy
Relatively large peptides that are absorbed intact may stimulate antibody formation
Nitrogen Metabolism
Leftovers of small intestine for to hindgut where fermentation produces odiferous compounds and AA are decarboxylated to produce toxic amines (ptomaines).
Ptomaines
cadaverine, putrescine, tyramine and histamine
Ruminant
Microbes convert nitrogen to microbial protein which fuels ruminant when microbe is digested.
Fate of Dietary Protein
1) Fermented in Rumen
2)Bypass rumen; digested in the small intestine
Deamination
Amino Acids used as energy sources, giving rise to
ammonia, branched-chain VFAs, carbon dioxide and
methane.
Rumen Ammonia
End-product of bacterial fermentation of dietary protein but starting point for microbial synthesis of bacterial AA & proteins.
Non-protein nitrogen (NPN) sources such as urea, biuret and uric acid (from poultry excreta) may be converted by microorganisms into bacterial protein.
Rumen Undegradable Protein (RUP)
Enters the abomasum & small intestine for digestion & absorption
Transamination
Synthesis of nonessential amino acids occurs in the liver where transaminases transfers AA group to organic acid.
*Reaction requires vitamin B6
C Skeleton
After product of transamination and deamination that can be used for making glucose, ketone bodies, or energy production.
Link Between Protein and Carbohydrate Metabolism
Transamination and resulting C-Skeleton
Glucogenic
All amino acids, except leucine and lysine.
Can use the C skeleton for glucose synthesis.
Ketogenic
Leucine and lysine are strictly ketogenic amino acids (forms ketone bodies) and can provide acetyl CoA as an energy source.
Glucogenic+Ketogenic
Isoleucine, phenylalanine, tyrosine, tryptophan
