AA catabolism -Brar

Question 1

What is required for ubiquitin tagging of proteins?

Answer 1

E1: ubiquitin activating enzyme
E2: ubiquitin-conjugating enzyme
E3: Ubiquitin-protein ligase

ATP is also required

Question 2

Steps of AA degradation

Answer 2

1. removal of nitrogen (liver is major site of protein degradation in mammals)–> producing alpha-keto-acids
2. alpha-amino groups are converted to ammonium ions by the oxidative deamination of glutamate
   * ammonium=toxic, most urea in blood is in the form of non-toxic glutamate
3. amino groups funneled into alpha-ketoglutarate via aspartate transaminase and alpine transaminase (ALT and AST)
   * elevation in these enzymes=hepatic damage = in LFT’s (liver functioning test) and are easily elevated
4. deamination : takes place in the mitochondria via glutamate dehydrogenase (uses NAD or NADP)

• carbon of degraded AA emerge as major metabolic intermediated
  5. ammonium is converted to urea, creating NADH–> urea=water soluble =excreted in urine

urea H2N-C=O-NH2

Question 3

Which AA are degraded to pyruvate?

Answer 3

Serine and threonine degradation can be directly deaminated to pyruvate –>glucagonic AAs enter the TCA cycle

glycine–> serine–> pyruvate
tryptophan–> alanine–> pyruvate
cysteine–> pyruvate
threonine–> amino acetone–>pyruvate

Question 4

7 major metabolic intermediates created by degradation of AA

Answer 4

Acetyl–CoA
Acetoacetyl–CoA
Pyruvate
α-Ketoglutarate
Succinyl–CoA
Fumarate
Oxaoloacetate

Question 5

Which AA are degraded to oxaloacetate?

Answer 5

aspartate

asparagine: hydrolysis to aspartate + NH4+ –>oxaloacetate

Question 6

Which AA are degraded to alpha-ketoglutarate?

Answer 6

glutamine + proline + arginine + histidine

all form glutamate –> alpha-ketoglutarate

*histidine has two pathways to get here–> many steps

Question 7

Which AA are degraded to succinyl-CoA?

Answer 7

Methionine, Valine, and Isoleucine
form propionyl CoA–> methylmalonyl CoA–> succinyl CoA

*methionine forms S-adenosylmethionine (SAM) –>

Question 8

Which AA are degraded to fumarate?

Answer 8

phenylalanine, tyrosine

phenylalanine (requires tetrahydrobiopterin)–> tyrosine–> fumarate and acetoacetate