Figure 4.

(A) Rates of ¹³CO₂ production (●) and O₂ consumption (■) when the DASN OxDC variant is incubated with varying concentrations of [1,2-¹³C₂]oxalate in 50 mM succinate buffer (pH 4.0), as determined by the MIMS-based assay. Independent measurements of the rates of formate (▼) and H₂O₂ (▲) production under identical reaction conditions were performed using standard assays. (B) Ratio of ¹³CO₂ production and O₂ consumption as a function of oxalate concentration at pH 4.0, as calculated from the MIMS-based rate measurements (●). The solid line represents the theoretical stoichiometry calculated from eq 4 (Discussion) assuming that the fraction of enzyme exhibiting oxidase activity is 0.09.