LOCALIZATION OF CARNITINE ACETYLTRANSFERASE ACTIVITY IN BROWN ADIPOCYTES OF THE RAT

Carnitine acetyltransferase (CAT), an enzyme involved in the beta-oxid ation of fatty acids, was localized in the interscapular brown adipose tissue of the rat. The reaction products were localized on the crista e and surface of the inner mitochondrial membrane. Thin needle-like re action products were abolished in control specimens incubated in eithe r acetyl CoA (substrate)-free medium or inhibitor (HgCl2)-containing m edium. They were also abolished when materials were fixed in a mixture of glutaraldehyde (1%) and paraformaldehyde (4%). Even when cristae w ere disintegrated in certain mitochondria contacting with nearby lipid droplets, the CAT activity was preserved in the rest of the intact cr istae. However, when a mitochondrion was completely engulfed in a lipi d globule, all cristae lost their CAT activity. These findings suggest an influence of lipid on the mitochondrial CAT activity. In the exper imental administration of bezafibrate, a hypolipidemic drug increasing the CAT activity, the CAT activity in the brown adipose tissue was si gnificantly increased (male 6.0-fold, female 2.0-fold) at two weeks of administration of bezafibrate except for castrated male and female ra ts. However, the localization of CAT activity in mitochondria was not altered by the administration of bezafibrate.