A new use of β-Ala-Lys (AMCA) as a transport reporter for PEPT1 and PEPT2 in renal brush border membrane vesicles from the outer cortex and outer medulla.

Integral membrane proteins PEPT1 and PEPT2 are essential for reabsorbing almost all hydrolysed or filtered di- and tripeptides alongside a wide range of peptidomimetic drugs in the kidney. The aim of this study was to investigate the potential use of the fluorophore-conjugated dipeptide β-Ala-Lys (AMCA) as a biosensor for measuring peptide transport activity in brush border membrane vesicles isolated from the outer cortex (BBMV-OC) and outer medulla (BBMV-OM) (representing PEPT1 and PEPT2 respectively). The vesicles were isolated using a dual magnesium precipitation and centrifugation technique. Intravesicular fluorescence accumulation was measured after incubating extra-vesicular media at pH6.6 and different concentrations of β-Ala-Lys (AMCA) with vesicles pre-equilibrated at pH7.4. Both BBMV-OC and BMMV-OM showed accumulation of an intravesicular fluorescence signal after 20min incubation. Changing the extra-vesicular pH to 7.4 caused a significant reduction in the β-Ala-Lys (AMCA) uptake into BBMV-OC at concentrations >100μM. When different concentrations of dipeptide, Gly-Gln was added, there was a significant inhibition of 100μM β-Ala-Lys (AMCA) uptake into BBMV-OC and BMMV-OM, reaching 69% and 80%, respectively. Kinetic analysis of β-Ala-Lys (AMCA) at 20min showed that the Km and Vmax were 783.7±115.7μM and 2191.2±133.9ΔF/min/mg for BBMV-OC, while BMMV-OM showed significantly higher affinity, but lower capacity at Km=93.6±21.9μM and Vmax=935.8±50.2ΔF/min/mg. These findings demonstrate the applicability of β-Ala-Lys (AMCA) as a biosensor to measure the transport activity of the renal-type PEPT1 and PEPT2 in BBMV-OC and BMMV-OM respectively.