... P-glycoprotein ⁄ Mdr3 ⁄ Mdr1a; IC, invariant carboxylate; MDR, multidrug resistance; NBD,nucleotide-binding domain; NBD1, N-terminal nucleotide-binding site; NBD2, C-terminal nucleotide-binding ... ⁄ D) in the nucleotide-binding domains (NBDs) of ATP-bindingcassette transporters is thought to be involved in the hydrolysis of thec-phosphate of MgATP, either by activating the attacking water ... showsalmost no labeling at all. Again, major changes in affinity for 8-azido-ATP cannot account for the differ-ences in labeling with 8-azido-nucleotide (Fig. 2) andas in the single-site mutants,...