Amino Acid Catabolism

Amino acids have 2 paths

NH4+ or C-skeleton

What happens to NH4+ ?

Turns into carbamoyl phosphate, and excreted through urea cycle

What happens to C skeleton

Turns into alpha-keto acid

What can happen to alpha-keto acid?

Turned into OAA goes through TCA —> gluconeogenesis —> glucose

what can the carbon skeleton be degraded to

• acetyl coa

• acetoactetyl coa

• pyuvate

• succinyl coa

• fumarate

• OAA

• A-Kg

Which TCA intermediates can the carbon skeleton be degraded to?

• OAA

• Succinyl CoA

• Fumarate

• A-KG

To remove nitrogen from an amino acid, carry out these two reactions

1. transamination

2. oxidative deamination

What happens to NH3 used for removing N?

Excreted

Transamination

AA —> alpha keto acid

A-KG —> glutamic acid

What amino acid is responsible for transamination

Amino transferase

Alanine transferase

Alanine —> pyruvate

A-KG —> Glutamic acid

Aspartic acid transferase

Aspartic acid —> OAA

A-KG —> Glutamic acid

What coenzyme used to break the phi (NH3/C) bond to allow for a transamination?

PLP coenzyme

What is the purpose of oxidative deamination?

To transfer NH4 to the liver to be excreted

Steps of an oxidative deamination

1. Use NAD+ to turn amino acid NH3+ into amino acid w/ C=O + NH4+

2. Use that NH4+ to turn glutamic acid into glutamine (requires ATP)

3. Glutamine can bring NH4 to liver

What two amino acids can NH4+ be transferred via to be in the liver?

Gln

Ala

Urea cycle net reaction

CO2 + NH4+ + Aspartic Acid + 3 ATP + H2O —> urea + fumarate + 2 ADP + 2Pi + AMP + Ppi

Cost of urea cycle

Because of AMP, cost is 4 ATP

First step of urea cycle

N becomes carbamoyl phosphate

How many ATP are redeemed by TCA ?

2.5, bringing cost to 1.5 T

The fumarate product of urea synthesis can do what?

turned into malate

turned into OAA (making NADH)

OAA —> Asp (Glu —> alpha-KG)

Ketogenic AA

Degraded to acetyl coA or acetoacetyl coA (FA path)

Glucogenic

TCA product or pyruvate

There is no net _____ in ___ from acetyl coA being formed

gain; C

Amino acids that break down to acetyl coA with pyruvate as intermediate

And are ketogenic (and glucogenic)

Ala

Ser

Gly

Cys

Trp

Thr

Amino acids that break down to acetyl coA with pyruvate as intermediate

Lys

Leu

Ketogenic only AAs

Lys

Leu

Glucogenic Only AAS

Met

Ile

Val

Glu

Gln

Arg

Pro

His

Asp

Asn

Glucogenic and Ketogenic AAs

Ala
Ser

Gly

Cys

Trp

Thr

Tyr

Phe

Tyr and Phe are special ketogenic and glucogenic AAs in that…

They break down to acetyl CoA (ketogenic) but have a non-pyruvate intermediate