Branched-chain lipids are important components of the human diet and are used as drug molecules, . ibuprofen. Owing to the presence of methyl groups on their carbon chains, they cannot be metabolized in mitochon-dria, and instead are processed and degraded in peroxisomes. Several dif-ferent oxidative degradation pathways for these lipids are known, including a-oxidation, b-oxidation, and x-oxidation.