The crystal structure of hydrazine synthase multiprotein complex isolated from the anammox organism Kuenenia stuttgartiensis implies a two-step mechanism for hydrazine synthesis: a three-electron reduction of nitric oxide to hydroxylamine at the active site of the gamma-subunit and its subsequent condensation with ammonia, yielding hydrazine in the active centre of the alpha-subunit. The alpha-subunit consists of three domains: an N-terminal domain which includes a six-bladed beta-propeller, a middle domain binding a pentacoordinated c-type haem (haem alphaI) and a C-terminal domain which harbours a bis-histidine-coordinated c-type haem (haem alphaII). This entry represents the middle domain of subunit alpha of hydrazine synthase (HZS) [1].

1: The inner workings of the hydrazine synthase multiprotein complex. Dietl A, Ferousi C, Maalcke WJ, Menzel A, de Vries S, Keltjens JT, Jetten MS, Kartal B, Barends TR; Nature. 2015;527:394-397. PMID:26479033