... with the histidine residue of the H-loop, and positions the ‘linchpin’ histidine in the correct orientation such that all atoms are then in position to favor abstraction of a proton from the attacking ... proteins. To answer thisquestion, we took advantage of the trypsin-sensitiveregion situated in the linker domain of Abcb1a. Fol-lowing trapping in the absence or presence of Vi andmild-trypsin treatment, ... 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...