OBSERVATIONS ON PEROXISOMES IN BROWN ADIPOSE TISSUE OF THE RAT

During cytochemical studies of brown adipose tissue from rat, cytoplasmic organelles that apparently show peroxidative activity have been observed. The majority of the organelles have a diameter of 0.1-0.8 µ and a finely granular homogeneous matrix and are delimited by a single unit membrane. No sign of a "crystalloid" was seen. In order to demonstrate the peroxidative activity of the peroxisomal enzyme catalase in the organelles, brown adipose tissue was incubated in a medium containing 3,3'-diaminobenzidine tetrahydrochloride, after prefixation in 3% glutaraldehyde. The activity was blocked by 3-amino-l,2,4-triazole (an inhibitor of catalase) but not by KCN. Omission of exogenous hydrogen peroxide did not inhibit the reaction in the organelles. It is concluded that rat brown adipose tissue contains peroxisomes and, since the abundance of these organelles varies according to the physiologic activity of the tissue, peroxisomes may have a role in the thermogenic metabolism of brown fat.