As summarized in Scheme 1, the whole catalytic cycle of LiP can be divided into three main stages. Among these stages, the activation of H2O2 (stage I), en route to the formation of Cpd I, can proceed via the well-established "Poulos-Kraut mechanism". Such mechanism via the heterolytic cleavage of the O-O bond has been extensively studied in heme-dependent metalloenzymes. As such, our study would focus on the stage II in Scheme 1, which is comprised of two consecutive ET steps. The first one involves the longrange ET from Trp171 to Cpd I, generating the Trp radical and Cpd II. Due to the basicity of Cpd II and the acidic pH environment, Cpd II would undergo the fast protonation to form the Fe(IV)-OH species, i. e. the protonated Cpd II. The formation of the protonated Cpd II could inhibit the back ET from Cpd II to the Trp radical. The second ET step involves the long-range ET from the lignin substrate to the Trp171 radical, leading to the intact Trp171 residue and the lignin cation radical species. In the stage III, the protonated Cpd II would be responsible for the second-round substrate oxidation. As the electron transfer mechanism in the stage III is expected to be similar to that in the stage II, the present study focuses on the electron transfer in the stage II (Figure ), with the obtained insights can be transferred to the stage III straightforwardly. In the following sections, we first performed QM/MM MD simulations to track the plausible ET mechanism with/without tartaric acid. In particular, the state-of-the-art QM/MM MD simulations can enable us to obtain equilibrated structures before/after the ET/PCET processes, as well as to capture the H-bonding fluctuation during the ET/PCET process. Afterwards, the nonadiabatic ET and PCET theories have been employed to estimate the ET and PCET rates.