Fig. 1

Schematic overview of reagents and products of relevance in the present work. a Illustration of the generally accepted reaction paths for cellulose-specific LPMOs. The reaction is preceded by the reduction of the active site copper by an electron donor, here exemplified by ascorbate. (i) When no substrate is present, the cuprous LPMO is reoxidised by the electron acceptor O₂ and produces H₂O₂ which can be quantified, e.g., using the peroxidase-based Amplex® Red fluorescence assay. (ii) When cellulose substrate is present, O₂ or H₂O₂ is used as the electron acceptor to oxygenate and ultimately cleave the cellulose to produce a mixture of un-, C1- or C4-oxidised sugars of various lengths. Soluble products can be separated by HPLC. (iii) In the presence of DMP or the related hydrocoerulignone, H₂O₂ is the preferred electron acceptor to oxidise the substrate to the colorimetric coerulignone, which can be measured by absorption at 469 nm. b Illustration of the interconversion between PHP and rPHP as utilised for the Kastle–Meyer presumptive blood test in forensic science. The Kastle–Meyer reagent is first prepared by reducing PHP with zinc dust, and it is then applied to, for instance a textile swab with 0.1 M H₂O₂ at pH 12. An immediate pink colour indicates the presence of blood