Amino Acid Metabolism

Question 0

What are the two key enzymes used in transamination? Where are they found? How can they be used to assess the function of the organ they are found in?

Answer 0

ALT = converts alanine to glutamate

AST = converts glutamate to aspartate

Liver

A high ALT or AST conc. in the blood indicates liver damage (liver function test)

Question 1

How are amino acids metabolised?

Answer 1

Amino group is transferred to a keto acid using alpha-ketoglutarate or oxalocaetate. The glutamate and aspartate that are produced as waste products are disposed of in the urea cycle.

Question 2

Describe deamination.

Answer 2

Amine group removed from amino acid, forming ammonia, which is then converted to urea (non-toxic)

Ammonia + Glutamate ——-> Glutamine ——–> Urea (kidney & liver)

Question 3

What do a complete or partial loss of urea cycle enzymes cause?

Answer 3

Complete loss = DEATH

Partial loss = hyperammonaemia & accumulation of urea cycle intermediates (affects neurotransmitter synthesis -> causes lethargy, irritability, mental retardation, seizures, coma, etc. & reduces TCA cycle -> disrupts energy cycle)

Management: low protein diet, replace amino acids with keto acids in diet

Question 4

Describe the mechanism of phenylketouria.

Answer 4

Autosomal recessive.

Phenyalanine ——–> Tyrosine ———-> Noradrenaline/Adrenaline
(phenylalanine hydroxylase)

Deficiency of phenylalanine hydroxylase so phenylalanine converted to phenylketones

Management: restrict specific amino acids in diet

Question 5

Describe the mechanism of homocystinuria.

Answer 5

Autosomal recessive
(CBS & Vitamin B6)
Homocysteine ———————-> Cysteine

Deficiency in CBS —–> Homocysteine converted methionine (Vitamin B12)

Management: provide Vitamin B

Affects connective tissue, muscles, CNS, & CVS (fibrillin-1 structure affected)