... of the trypsin-sensitiveregion situated in the linker domain of Abcb1a. Fol-lowing trapping in the absence or presence of Vi and mild-trypsin treatment, the trypsin degradation pro-ducts of ... E552 in NBD1 and E1197 in NBD2. Tofurther characterize the role of these residues in catalysis, we created in Abcb1a the single-site mutants E552D, N and A in NBD1, and E1197D,N and A in NBD2, ... trapping isalmost normal. By contrast, when the charge isremoved, as in the glutamine (length of the side chainmaintained) and asparagine (shorter side chain)mutants, then trapping in the...