CYSTEINE RESIDUES ARE NOT ESSENTIAL FOR UNCOUPLING PROTEIN FUNCTION

The uncoupling protein (UCP) of brown adipose tissue is a regulated pr oton carrier which allows uncoupling of mitochondrial respiration from ATP synthesis and, therefore, dissipation of metabolic energy as heat . In this article we demonstrate that, when UCP is expressed in Saccha romyces cerevisiae, it retains all its functional properties: proton a nd chloride transport, high-affinity binding of nucleotides and regula tion of proton conductance by nucleotides and fatty acids. Site-direct ed mutagenesis demonstrates that sequential replacement by serine of c ysteine residues in the UCP does not affect either its uncoupling acti vity or its regulation by nucleotides and fatty acids, and therefore e stablishes that none of the seven cysteine residues present in the wil d-type UCP is critical for its activity. These data indicate that tran sport models involving essential thiol groups can be discounted and th at chemical modification data require critical re-evaluation.