Biochemical reactions in peroxisomes

The electron micrograph (1) shows peroxisomes
in a section of rat liver. The dark striated
structures within the organelles consist of
urates (peroxisomes contain an enzyme that
oxidizes uric acid). Peroxisomes have both catabolic
(substances are degraded) and anabolic
(substances are synthesized) functions (2). Two
biochemical reactions are especially important:
a peroxisomal respiratory chain and the !-oxidation
of very long-chain fatty acids. In the peroxisomal
respiratory chain (3), certain oxidases
and catalases act together. Specific substrates of
the oxidases are organic metabolites of intermediary
metabolism. Very long-chain fatty
acids are broken down by !-oxidation (4) in a
cycle with four enzymatic reactions. Energy
production in peroxisomes is relatively inefficient
compared with that of mitochondria.
While free energy in mitochondria is mainly
preserved in the form of ATP (adenosine triphosphate),
in peroxisomes it is mostly converted
into heat. Peroxisomes are probably a
very early adaption of living organisms to oxygen.