Peroxisomes Flashcards
What do peroxisomes do?
fatty acid degradation and reactive oxygen metabolism (common)
What are specialised functions of peroxisomes?
part of photorespiration
part of penicillin biosynthesis
glycolysis of trypansomes
Which human tissues are peroxisomes present in?
Liver
Brain
Kidney
What are the 4 metabolic functions of peroxisomes?
- branched chain fatty acid shortening
- Ether lipid (plasmalogen) biosynthesis
- Bile acid synthesis
- Glyoxylate detoxification
What does B-oxidation result in the removal of?
2 carbon units as acetyl CoA
Where does B-oxidation take place?
plants - ONLY peroxisomes
Mammals - mitochondria AND peroxisomes
What are the 2 consequences of peroxisome malfunction?
- Peroxisome Biogenesis Disorder
- Single Gene deficiency
What are Peroxisome Biogenesis Disorders?
failure to assemble the organelle
Zellweger Syndrome spectrum
What happens during peroxisomal protein import?
protein binds to PEX5 receptor by PTS1 signal
receptor docks to protein complex on peroxisome membrane
protein transported in
receptor recycled
What happens during ZS so that peroxisomal protein import doesn’t happen?
receptor or component of docking/recycling complexes are defective
What are the 4 disorders of the Zellweger spectrum?
Zellweger syndrome
Neonatal adrenoleukodystrophy
Infantile Refsum Disease
RCDP
How are disorders of the Zellweger spectrum diagnosed?
look at biochemical pathways affected
defective gene undergoes molecular testing
treatment primarily support symptoms
What are 2 disorders that arise from mutation in specific enzyme activity within peroxisomes?
X-ALD
PH1
What is X-ALD
affect boys - inherit from mother
disorder of peroxisomal beta oxidation
What gene is involved in X-ALD?
ABCD1 gene
encodes membrane protein ALDP which belonds to ATP binding Cassette - transports long fatty acid chains into peroxisomes
How can X-ALD be diagnosed?
accumulation of very long chain fatty acids
What are the symptoms of CCALD (X-ALD)?
inflammatory demyelination of neurones in brain
death within 3 years
What are the symptoms of AMN (X-ALD)?
slower progressing
muscle weakness
impaired adrenocortical function
What are treatments of X-ALD?
adrenal hormone therapy
diet - restricted fat
Bone marrow transplant (high risk)
Gene therapy
What is PH1?
single gene disorder
autosomal recessive condition
defects in Alanine Glyoxylate Transferase (peroxisomal liver enzyme)
What does AGT enzyme in the peroxisome do?
converts glyoxylate to glycine
What can PH1 be caused by?
No AGT at all
OR
AGT mis-targeting to mitochondria by 2 mutations changing the aa’s
What are treatments of PH1?
high dose vitamin B6
avoid foods with high oxalate
liver transplant
kidney transplant
What plant fungi diseases are peroxisomes essential for?
rice blast fungus
Anthracnose fungi
produce appressoria with melanised walls
