FIGURE 7.

Vesicular transport of an N-acetylated dipeptide library shows that ABCC5 is a general C-terminal glutamate dipeptide transporter. Inside-out membrane vesicles with or without ABCC5 were incubated (10 min, 37 °C) with a library of 20 N-acetylated, C-terminal glutamate dipeptides (∼10 μm per peptide) in the presence and absence of 5 mm ATP. The relative amount of each peptide in the vesicles was determined using LC-MS and normalized on the peptide signal in the original peptide library. Poor LC-MS sensitivity for (Ac)Lys-Glu resulted in a low signal in the input library and undetectable levels in vesicles. We were unable to discriminate (Ac)Ile-Glu and (Ac)Leu-Glu because of their identical mass. Hence the uptakes of both of these dipeptides are labeled (Ac)(iso)Leu-Glu. The data are presented as means plus S.D. (n = 4). AU, arbitrary units.