Immunocytochemical localization of two peroxisomal enzymes of lipid beta-oxidation in specific granules of rat eosinophils.

Peroxisomes contain a system for beta-oxidation of fatty acids which differs from the mitochondrial system and is associated with hydrogen peroxide formation. We show that two enzymes: enoyl-CoA hydratase and 3-ketoacyl-CoA thiolase of the peroxisomal system are present in specific granules of rat eosinophils. Both enzyme proteins were purified from rat liver and monospecific antibodies were raised in rabbits. Eosinophils from peripheral blood and tissue eosinophils from the wall of intestine, fixed by glutaraldehyde and embedded in Epon were investigated. The postembedding immunocytochemical procedure with protein A-gold technique was used. The gold particles representing the antigenic sites for both enzymes were present only in specific granules of eosinophils with no immune deposits in mitochondria, nucleus and the cytoplasm. Although gold particles were found over the entire domain of the granule, the electron dense paracrystalline inclusions contained more gold than the granule matrix. Control preparations incubated with nonspecific IgG and protein A-gold complex alone were negative. These findings indicate that in specific granules of eosinophils both peroxisomal and lysosomal enzymes share the same intracellular compartment. The peroxisomal lipid beta-oxidation in eosinophils may be involved in generation of hydrogen peroxide, which has a crucial role in killing of metazoon parasites.