Important amino acid residues of potato plant uncoupling protein (StUCP)

Chemical modifications were used to identify same of the functionally impor tant amino acid residues of the potato plant uncoupling protein (StUCP), Th e proton-dependent swelling of potato mitochondria in K+-acetate in the pre sence of linoleic acid and valinomycin was inhibited by mersalyl (K-i= 5 mu M) and other hydrophilic SH reagents such as Thiolyte MB, iodoacetate and 5 ,5'-dithio-bis-(2-nitrobenzoate), but not by hydrophobic N-ethylmaleimide. This pattern of inhibition by SH reagents was similar to that of brown adip ose tissue uncoupling protein (UCP1). As with UCP1, the arginine reagent 2, 3-butadione, but not N-ethylmaleimide or other hydrophobic SH reagents, pre vented the inhibition of StUCP-mediated transport by ATP in isolated potato mitochondria or with reconstituted StUCP. The results indicate that the mo st reactive amino acid residues in UCP1 and StUCP are similar, with the exc eption of N-ethylmaleimide-reactive cysteines in the purine nucleotide-bind ing site.