Abstract
In mammalian brown adipose tissue, uncoupling protein 1 (UCP1), triggers a proton leak and converts the energy into heat. Although the recent finding of plant UCPs in non-thermogenic tissues has precluded their involvement in thermogenesis, there are few studies of them in thermogenic tissues. Therefore, we analyzed two cloned UCP cDNAs, SfUCPa and SfUCPb, isolated from the thermogenic spadix of skunk cabbage. We show that SfUCPA, not SfUCPB, is the major uncoupling protein and that it is integrated into the inner mitochondrial membrane. Using spadix mitochondria, we examined the uncoupling activity of SfUCPA. Although SfUCPa transcripts were constitutively expressed in various tissues irrespective of thermogenic stages, SfUCPA protein existed only in the thermogenic tissue or stage. Quantitative immunoblot analysis revealed that SfUCPA was an abundant protein in spadix mitochondria. Our results suggest that SfUCPA may be involved in the heat production of skunk cabbage.
