31 - Protein Digestion, Absorption And Metabolism

Front 1

Protein digestion in monogastrics: Oral cavity

Back 1

Mechanical breakdown, no proteolytic digestion

Front 2

Protein digestion in monogastrics: Corpus and Fundus

Back 2

HCl from parietal cells hydrolyzes some bonds and activates pepsinogen from chief cells to pepsin

Front 3

Protein digestion in monogastrics: Duodenum

Back 3

Enterokinase activates trypsin which in turn, activates other zymogens

Front 4

Protein digestion in monogastrics: Jejunum and Ileum

Back 4

Absorption of di and tripeptides and amino acids

Front 5

Phases of Intestinal Peptide Absorption

Back 5

Pancreatic Phase

Mucosal Phase

Delivery Phase

Front 6

What happens in pancreatic phase?

Back 6

Protein turned into oligo-peptides through exo and endo peptidases (pepsin)

Oligo-peptides are turned into di and tripeptides through enterokinase (trypsin and oligo peptidases)

Front 7

What happens in mucosal phase?

Back 7

Pinocytosis of colostrum IgG's (<48hrs)

AA carrier transports AAs

Some peptides penetrate cell

PepT1 transporter transports peptides in by working with Na/H transporter (PepT1 requires H+)

Front 8

What happens in delivery phase?

Back 8

IgG's brought to lymph

Peptides and AAs transported to portal vein

Front 9

What is the difference between the PepT1 receptor (for protein) and the SGLT1 receptor (for CHOs)

Back 9

PepT1 can transport both di and tri peptides

SGLT1 can only pick up mono-saccharides

Front 10

PepT1 found in?

Substrates for PepT1?

Back 10

Major tissues: Intestine, Kidney, lysosomes

Substrates: Di and Tri peptides, protons

Front 11

What do endopeptidases do? give examples of some endopeptidases

Back 11

Hydrolyze bonds in middle of protein to generate small peptides

Ex. Pepsin, rennin, trypsin, chymotrypsin, elastase

Front 12

What do exopeptidases do? give examples of exopeptidases

Back 12

Release AA from ends of peptide chains

Ex. Carboxypeptidases A and B

Front 13

Aromatic AAs

Back 13

Phe

Tyr

Trp

Front 14

BCAAs

Back 14

Ile

Leu

Lys

Val

Front 15

Glucogenic AAs

Back 15

Gly, Ala, Val, Ile, Phe, Trp, Met, Pro, Ser, Thr, Tyr, Asp, Cys, Gln, Asp, Glu, His, Arg

Front 16

Ketogenic AAs

Back 16

Lys, Leu

Front 17

Glucogenic and Ketogenic AAs

Back 17

Phe

Tyr

Trp

Thr

Ile

Front 18

Aromatic AAs are largely metabolized by?? For what??

Back 18

Liver

Energy and biosynthesis

Front 19

BCAAs mostly pass into _______________ but are mainly metabolized in ______________ via ______________

Back 19

Systemic circulation

Muscle

BCAA transaminase

Front 20

Glu is used for?

Back 20

Gluconeogenesis in the kidney

Front 21

Glutamate dehydrogenase reaction:

1. Key to doing what?

2. Significance in higher animals (what does this lead to)

Back 21

1. Key to fixing/removing NH3-N to/from alpha amino groups

2. Higher animals deficient in alpha-KG so they have: limited ability to carry out this step, need dietary alpha-amino groups, and can't efficiently deal with excess NH3

Front 22

Tranamination is a critical reaction for

Back 22

Metabolic (N) economy

Front 23

Transamination is an equilibrium reaction, meaning that depending on concentration....

(provide example)

Back 23

Amino acids can be deaminated or keto-acids can be aminated

- In liver/renal failure: dietary supplementation of keto-acids can clean up excess amino groups

Front 24

Examples of common transamination reactions:

Back 24

alpha-ketoglutarate --> Glutamate

Pyruvate --> Alanine

Oxaloacetate --> Aspartate

Front 25

Microbial protein flow is ______% of total protein flow in the intestine

Back 25

45-60%

Front 26

What makes up Metabolizable Protein?

Back 26

Microbial protein + RUP + Endogenous protein

Front 27

What makes up endogenous protein?

Back 27

Sloughed cells, intestinal enzymes, etc

Front 28

How is microbial protein made/used?

Back 28

1. Absorbed peptides turned into protein

2. Intracellular synthesis from VFAs and NH3

3. Uses AA for own energy

Front 29

Why do we feed urea to cattle?

Back 29

Relatively inexpensive N2 source for replacing protein content of diet

Front 30

How much urea can we feed to cattle?

Back 30

Upper limit: 1% urea of diet DM or 30% of RDP

*Optimal when CP <12%

Front 31

What is the problem with urea and low quality forages?

Back 31

Imbalance between the rate of ammonia availability and the availability of carbon for the microbes to produce microbial protein and thus ammonia is absorbed into blood stream (bad)

Front 32

Clinical signs of urea toxicity

Back 32

Appear 20-30mins after urea ingestion

-Rapid and laboured breathing

-Tremors, incoordination, inability to stand and tetany

Front 33

Mechanisms of Urea Toxicity

Back 33

1. Increase in rumen ammonia = increase in rumen pH

2. As pH increases, shifts from NH4+ to NH3

3. NH3 absorbed much faster than NH4+

4. Liver capacity to convert NH3 to urea exceeded

5. NH3 accumulates in blood (TOXIC)

Front 34

How can you treat urea toxicity?

Back 34

1. Oral drench with 5% acetic acid (to shift equilibrium back to NH4)

2. Cold water drench (decreases urea hydrolysis)

3. Rapid rumen evacuation (doesn't work great)

Front 35

How do you prevent urea toxicity?

Back 35

Proper feed mixing

Slow dietary adaptation and ad lib feeding

Front 36

What is the rate limiting enzyme for urea synthesis in liver?

Back 36

Arginase

Front 37

What happens to urea?

Back 37

Excreted in urine (30%)

Most Recycled through saliva or rumen wall through UT (70%)

Front 38

Ruminal protein degradation steps

Back 38

1. Microbial proteases & peptidases cleave peptide bonds and release AAs

2. AAs deaminated by microbes, releasing NH3 and Keto-acids

Front 39

Proteins leaving rumen

Back 39

Microbial protein

Bypass dietary protein

Secretions

Front 40

Synthesis of microbial proteins: summary

Back 40

Microbes use NH3, keto-acids, and energy to synthesize their own AAs

Front 41

Limitation of microbial protein synthesis

Back 41

Synchronized availability of readily fermentable CHOs and NH3

Front 42

Turnover of microbial proteins

Back 42

Microbes lysed by lysozymes in abomasum and releases microbial protein which is digested by proteases

Front 43

Similarities between ruminant and non-ruminant protein metabolism

Back 43

Metabolic pathways similar at tissue level

Can synthesize non-essential AA

Can't synthesize essential AA (need from diet)

Tissue proteins constantly undergoing turnover

Limited AA storage - need constant supply

Front 44

Differences between ruminant and non-ruminant protein metabolism

Back 44

Generally not concerned with AA composition of dietary protein in ruminants

Ruminants are highly inefficient at converting dietary protein to milk or meat protein (70-75% of N2 intake excreted in urine and feces)

Front 45

Why are we generally not concerned with AA composition of dietary protein in ruminant diets?

Back 45

Type of feed has minimal effect on AA composition of bacteria & protozoa leaving rumen, whereas AA composition of microbes reaching duodenum is similar

AND

Biological value of microbial protein ~80%