Utilization and excretion of AA and Nitrogen

Question 1

Protein metabolism

Answer 1

1.become tissue protein
2. become amino acids (acetyl coA and CAC; ketones; carbohydrates)
3.non-protein nitrogen derivatives such as DNA

Question 2

Protein breakdown

Answer 2

• 25-95% of AA catabolized in enterocytes or by bacteria

-5-75% absorbed in portal vein and metabolized in liver

Question 3

Ammonia/ammonium

Answer 3

produced from the oxidation of AAs

*in equilibrium with each other in aqueous solutions

Question 4

Transport of ammonia

Answer 4

moves easily across biological membranes

**ammonium difficult to transport

Question 5

Deamination of AAS

Answer 5

bacterial urease in the colon converts the urea into NH3 (ammonia)

Question 6

Ammonia in portal vein vs. hepatic vein

Answer 6

Portal vein: 250microM
*very high levels of ammonia in portal vein, meaning the liver needs to convert it to urea

Hepatic vein: 30 microM

Question 7

Pyruvate/alanine part of urea cycle

Answer 7

1. Pyruvate converted to alanine through transamination by alanine transaminase (ALT). Alanine carries N to liver
2. Alanine deaminated in liver into NH2 and pyruvate
3. NH2 used to make urea and pyruvate used to make glucose

Question 8

Cahill cycle

Answer 8

-occurs in post-absorptive state
-free AAs (especially alanine and glutamine) are released from muscle into circulation
>Alanine is key gluconeogenic AA, and NH2 is converted to urea

Question 9

AA extraction and release

Answer 9

Occurs post meal

-Release AA- splanchnic tissues

-extract AA- peripheral muscles

Question 10

Urea

Answer 10

-water soluble
-non-toxic
-synthesized in liver (mammals) but requires energy
-not ionized at physiological pH meaning it is easily transported

Question 11

Biosynthesis of urea

Answer 11

1.Transmination
2. Oxidative deamination of glutamate
3. Ammonia transport
4. Urea cycle

Question 12

Transamination

Answer 12

-freely reversible
-Requires pyridoxal phosphate (derivative of vit B6)
-All of the amino Nitrogen can be concentrated in L-glutamate for transport

Question 13

Oxidative deamination

Answer 13

Glutamate undergoes oxidative deamination
-Transfer amino nitrogen to alpha-ketoglutarate catalyzed by hepatic L-glutamate dehydrogenase (GDH)
-release nitrogen as NH3

**freely reversible

Question 14

Liver GDH

Answer 14

-inhibited by ATP, GTP, and NADH

-activated by ADP

Question 15

Ammonia Transport

Answer 15

Ammonia can be produced by enteric bacteria and extra-hepatic tissues.

Glutamine synthetase fixes NH4 as glutamine. Glutamine holds ammonia in a non-toxic form

Question 16

Glutamine to Glutamate reaction

Answer 16

Irreversible in the direction of glutamate and NH4 formation

> allows for ammonia to be free in the liver so that it can be synthesized into urea

Question 17

Urea cycle

Answer 17

1.Condensation of CO2 ammonia and ATP into carbomyl phosphate
2.Carbomyl phosphate and ornithine= citrulline
3. citrulline and aspartate into arginosuccinate
4.cleavage of arginosuccinate into arginine and fumarate
5. cleavage of arginine into urea and ornithine

Question 18

Rate limiting step of urea cycle

Answer 18

Condensation of CO2 ammonia and ATP into carbomyl phosphate
>occurs by carbomyl phosphate synthase I in mitochondria

Question 19

Blood urea nitrogen

Answer 19

-BUN, PUN, MUN- indicate liver and kidney health
-urea travels from the liver to the kidneys to be excreted

Question 20

Decreased BUN

Answer 20

-chronic, severe liver disease
-low protein diets
-drugs causing diuresis
-overhydration
-increased protein synthesis

Question 21

Increased BUN

Answer 21

-blood loss
-dehydration
-recent high protein meal
-kidney infection or inflammation
-bladder or urethral obstruction

Question 22

BUN and AA adequacy

Answer 22

-There is an AA threshold, which is the max amount of AA needed. If above this threshold, then would expect there to be an increased level of urea in the blood

Question 23

Energy cost of urea synthesis

Answer 23

6.5 ATP/mol of urea

**takes a lot of energy to get rid of excess protein

Question 24

Gross energy

Answer 24

-total possible energy from 100% combustion of feed

Question 25

Digestible energy

Answer 25

-Energy when taking into account the energy lost in feces

Question 26

Metabolizable energy

Answer 26

Energy left after accounting for loss in feces, urine, gas

**energy actually available for use

Question 27

Net energy

Answer 27

the total energy left after removing energy lost to feces, urine, gas, and heat (from metabolic processes)

Question 28

Urea cycles role in heat increment

Answer 28

-urea cycle plays a large role in het increment therefore high crude protein ingredients will result in increased urea cycle and therefore less energy available from the original food intake

Question 29

Pet food energy use

Answer 29

Use metabolizable energy adjusted for N