The Structure of the Hyponitrite Species in a Heme Fe-Cu Binuclear Center

摘要

The formation of the hyponitrite species from two NO molecules is the key intermediate in the reduction of NO to N2O in denitrification. The reaction is used by bacteria as an alternative to oxygen-based respiration. The bacterial nitric oxide reductase (Nor) and the ba3-oxidoreductase from Thermus thermophilus catalyze the reaction: 2 NO + 2 e- + 2 H+→N2O + H2O. The latter enzyme contains a homodinuclear copper complex (CuA), one low-spin, six-coordinate heme b, and a binuclear center that consists of CuB and a high-spin heme a3 in which the catalytic reactions take place. A full elucidation of the structure and the electronic configuration of various intermediates are of profound importance for understanding the mechanism by which the enzymes form and cleave the N-N and N-O bonds, respectively.