| Assay Method Information | |
| | Biochemical QPCT and QPCTL Activity Assay |
| Description: | QPCT or QPCTL dependent conversion of N-terminal glutamine to pyroglutamate of CD47 was monitored via MALDI-TOF MS. Test compounds were dissolved in 100% DMSO and serially diluted into clear 1,536-well microtiter plates. Enzymatic reactions were set up in assay buffer containing 20 mM Tris pH 7.5, 0.1 mM TCEP, 0.01% BSA, and 0.001% Tween20. 2.5 μL of 2× concentrated QPCTL (in-house) or QPCT (Origine #TP700028) enzyme in assay buffer (0.5 nM final concentration, columns 1-23) or plain assay buffer (columns 24) were added to each well. The plates were incubated for 10 min in a humidified incubator at 24° C. Subsequently, 2.5 μL of CD47 peptide substrate surrogate (19QLLFNKTKSVEFTFC33) was added to each well (final concentration: 10 μM for QPCTL/20 μM for QPCT). The plates were mixed for 30 sec at 1,000 rpm and subsequently incubated for 40 min in a humidified incubator at 24° C. After incubation, the enzymatic reaction was stopped by adding 1 μL containing stable isotope labeled internal standard peptide 19[Pyr]LLFN(K)TKSVEFTFC33 (final concentration 4.0 μM) as well as SEN177 (final concentration 10 μM). The plates were sealed with an adhesive foil, mixed for 30 s at 1,000 rpm and stored at room temperature until preparation of the MALDI target plates. MALDI target plates were prepared as described previously. |
| Affinity data for this assay | |
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