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. Author manuscript; available in PMC: 2020 Dec 31.
Published in final edited form as: Biochemistry. 2019 Jun 26;58(52):5259–5270. doi: 10.1021/acs.biochem.9b00140

Figure 3.

Figure 3.

Affinity of the CpfC–ChdC complex that is consistent with a transient protein–protein interaction. A preformed coproporphyrin–CpfC complex was generated by equilibrating 5 μM coproporphyrin with 20 μM CpfC (red). ChdC was added titrimetrically (gray spectra, representing additions leading to final pre-equilibrated concentrations of 40, 80, 100, 200 and μM ChdC) until the spectral changes ceased and a final spectrum was obtained (black). The top inset shows the change in absorbance at 418 nm as a function of the titrated concentration of ChdC (red). This was fit to the Langmuir–Hill equation to determine a KD for the coproporphyrin–CpfC complex with ChdC. In blue, similar data and a curve fit showing CpfC complexation with a preformed coproporphyrin–ChdC complex are shown (bottom inset, blue). These data were used to compute a dissociation constant for the two proteins, ChdC and CpfC.