Ferroheme/Ferriheme Directly Involved in the Synthesis and Decomposition of Hydrazine as an Electron Carrier during Anammox
Zhenxin Wang, Qilin Yu, Zhiqiang Zhao, Yaobin Zhang
Abstract
Anammox bacteria performed the reaction of NH 4 + and NO with hydrazine synthase to produce N 2 H 4, followed by the decomposition of N 2 H 4 with hydrazine dehydrogenase to generate N 2 . Ferroheme/ferriheme, which serves as the active center of both hydrazine synthase and hydrazine dehydrogenase, is thought to play a crucial role in the synthesis and decomposition of N 2 H 4 during Anammox due to its high redox activity. However, this has yet to be proven and the exact mechanisms by which ferroheme/ferriheme is involved in the Anammox process remain unclear. In this study, abiotic and biological assays confirmed that ferroheme participated in NH 4 + and NO reactions to generate N 2 H 4 and ferriheme, and the produced N 2 H 4 reacted with ferriheme to generate N 2 and ferroheme. In other words, the ferroheme/ferriheme cycle drove the continuous reaction between NH 4 + and NO. Raman, ultraviolet–visible spectroscopy, and X-ray absorption fine structure spectroscopy confirmed that ferroheme/ferriheme is involved in the synthesis and decomposition of N 2 H 4 via the core Fe II /Fe III cycle. The mechanism of ferroheme/ferriheme participation in the synthesis and decomposition of N 2 H 4 was proposed by density functional theory calculations. These findings revealed for the first time the heme electron transfer mechanisms, which are of great significance for deepening the understanding of Anammox.