Unraveling the roles of the reductant and free copper ions in LPMO kinetics

The strong impact of low amounts of free copper on LPMO reactions with ascorbic acid and O₂, i.e. the most commonly used conditions when assessing LPMO activity, likely explains reported variations in LPMO rates. The observed differences between ascorbic acid and gallic acid show a way of making LPMO reactions less copper-dependent and illustrate that reductant effects on LPMO action need to be interpreted with great caution. In clean reactions, with minimized generation of H₂O₂, the (O₂-driven) LPMO reaction is exceedingly slow, compared to the much faster peroxygenase reaction that occurs when adding H₂O₂.