Figure 2.

ATP-dependent peptide transport into proteoliposomes. Peptide translocation into proteoliposomes was assayed at 32°C for 2 min by using 1 μM of the ¹²⁵I-labeled peptide, RRYNASTEL (K_D = 516 nM), in the presence or absence of ATP (3 mM). TAP-bound but not transported peptide was competed out by washing with 9 μM of the unlabeled peptide RRYQKSTEL (K_D = 164 nM). To demonstrate that transport is peptide specific, the assay was performed in the presence of a 400-fold molar excess of unlabeled peptide and ATP. To show TAP-specific transport, the TAP-inhibitor ICP47 (10 μM) was added in the presence of ATP. The background results from peptide bound to but not transported by TAP. Data were obtained from duplicate measurements.