Fig. 3: FTIR analysis of PVC samples after treatment with the catalase-peroxidase KlebCP.

The figure shows FTIR spectra of high molar mass (panel A) and low molar mass (panel B) PVC powders (100 mg/mL) after 96 h of incubation at 30 °C with or without 10 µM KlebCP in 50 mM Tris-HCl buffer, pH 8.0, containing 300 mM NaCl. Each FTIR trace represents the average of spectra obtained for 3 independently prepared reactions. The samples were first analyzed without removing the residual enzyme (orange trace) and then subjected to additional washing with Milli-Q water, as indicated in the figure (green trace). The light orange trace (superposed on the orange trace, no offset) represents FTIR spectra obtained for the control reactions lacking the enzyme. The FTIR data obtained for KlebCP in the absence of any plastics is shown as a purple trace (“KlebCP alone”), whereas the FTIR spectra of KlebCP-treated PVC and buffer-treated PVC that were reported by Zhang et al. are shown in red and light red, respectively (superposed spectra; no offset between these two). These previously published spectra were plotted using the source data file provided with the original paper²³ and normalized as described below. Comparison of the traces clearly shows that the peaks previously claimed to indicate enzymatic oxidation of PVC (marked with black arrows) result from the adsorbed residual protein and not from true reaction products. The data were acquired with 8 cm⁻¹ resolution. The absorbance signals were normalized using the C–H bend peak ( ≈ 1250 cm⁻¹) as the reference in PVC-containing samples and the amide I peak ( ≈ 1650 cm⁻¹) in the protein-only sample. Note that quantitative comparison between the data obtained for KlebCP alone and for the samples containing PVC is not possible due to the difference in normalization. Source data are provided as a Source Data file.