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.