... substrate-binding and substrate-releasing conform-ational states. The consecutive steps of the catalytic cycleappear to be discriminated by the changing affinity of Pgpto the UIC2 mAb [18,30]. Reactivity of ... nonsubstrate agents interfering with theATPase cycle. To study this question, we compared theeffects of Pianalogues (Vi,BeFx,AlF4), trapping nucleotidesat the catalytic site of Pgp, and of ... Viintermediate occurs randomly at one of the two nucleotide-binding sites of Pgp, but not simulta-neously [14–16]. It has been demonstrated in photoaffinitylabeling experiments that the affinity...