Fatty acid utilization and purine nucleotide binding in brown adipose tissue of genetically obese (ob/ob) mice

The activities of the main enzymes involved in fatty acid utilization i.e. palmitoyl CoA synthetase as well as peroxisomal and mitochondrial beta-oxidation were measured in brown adipose tissue homogenates of lean and ob/ob mice kept at 23 degrees C or acclimated at 4 degrees C. The proton conductance pathway, i.e. the number of purine nucleotide (GDP) binding sites and the percentage of 32,000 polypeptide in brown adipose tissue mitochondria were also measured. In the ob/ob mice at 23 degrees C, the specific activities of the palmitoyl CoA synthetase and of the beta-oxidation as well as the number of GDB binding sites were lower than in the lean mice by 26%, 43% and 37%, respectively. The percentage of 32,000 polypeptide, however, was the same in both groups. In the ob/ob mice at 23 degrees C, the lower homogenate beta-oxidation specific activity was due to the fact that the peroxisomal and mitochondrial specific activities were 44% and 37% lower, respectively. Cold acclimation at 4 degrees C was found to cause an increase of the palmitoyl CoA synthetase specific activity, of the palmitoyl CoA synthetase and peroxisomal beta-oxidation total activities and of the number of GDP binding sites, in both lean and ob/ob mice. Cold acclimation increased the percentage of 32,000 polypeptide in the ob/ob mice only.