Fig. 4.

Functional rescue of AOAA-inhibited CBS by Ser. A, B Determination of IC₅₀ of AOAA in both tScCBS (A) and HsCBS in the absence and presence of 500 µM SAM (B). The determined IC₅₀ values from the best fit are shown. C–E Rescue of CBS activity by preincubation with 1 mM Ser (green) followed by AzMC assay (C–E) and CBL-LDH coupled-coupled assay in the presence of 5 mM Cys (or 5 mM Ser) and 2 mM Hcy from the enzyme inhibited by 200 µM AOAA (cyan) compared to untreated enzyme (black) or enzyme pretreated with 1 mM Ser (magenta). Panels C, D and E show the results for tScCBS, HsCBS in the absence and in the presence of 500 µM SAM, respectively. (F, G) Ser, but not Cys as a substrate rescued enzymatic activity of AOAA-inhibited tScCBS, HsCBS in the absence and in the presence of 500 µM SAM using the CBL-LDH coupled-coupled assay for both the canonical (5 mM Ser + 2 mM Hcy; F) and alternative reactivities (5 mM Ser + 2 mM Hcy; G)