intracellular organelle found in all nucleated cells; have a single membrane, same size as mitochondria, abundant in liver
rich in oxidative enzymes – use hydrogens from hydrated substrate to form hydrogen peroxide which is changed into water
O2 becomes H2O2 (hydrogen peroxide) via oxidases; H2O2 becomes 2H2O via catalase with peroxidase reaction substrate (methanol, nitrites, etc) or gives off an O2
interest in the context of protein targeting
proteins synthesized on free ribosomes in cytosol and imported post-translationally into the peroxisomes
peroxisomes arise from pre-existing peroxisomes: ½ life is ½ to 2 days, turnover by microautophagy
way proteins are imported into the peroxisome
3 signals – PTS1, PTS2, unknown
pex5 finds PTS1 signal; pex7 finds PTS2 signal
after all 3 receptors bind with signal, they all import together through a receptor (docking site) – requires ATP
Functions of Peroxisomes
(1) Anabolic:
Plasmalogen biosynthesis (25% of plasma membrane), bile acid synthesis, glyoxalate transamination, gluconeogenesis, deamination of amino acids
(2) Catabolic:
b oxidation of FA (catabolize FA of chain lengths of 12 carbons or more to acetyl CoA and short acyl CoA, or acyl carnitine end products); substrate oxidation using O2 to generate H2O2 which is decomposed by catalase; purine and polyamine catabolism
Biogenesis and Turnover of Peroxisomes
peroxisomal membrane lipids are synthesized in the ER and carried by phospholipid carrier proteins
both matrix and membrane proteins are imported post-translationally into pre-existing peroxisomes through specific targeting signals and receptors
new peroxisomes form by budding or division of pre-existing peroxisomes
peroxisomes are believed to turnover by autophagy
Human Peroxisomal Disorders
disorders of peroxisomal biogenesis
(1)
Zellweger Syndrome: contains peroxisome ghosts with membrane proteins but lack matrix proteins; complementation analysis (genes a- and b-, fuse a- x b- Þ cured (works normally))