Bacterial nitric oxide reductase (NorBC) models employing click chemistry

Jill B Harland; Subhra Samanta; Nicolai Lehnert

doi:10.1016/j.jinorgbio.2023.112280

Bacterial nitric oxide reductase (NorBC) models employing click chemistry

J Inorg Biochem. 2023 Sep:246:112280. doi: 10.1016/j.jinorgbio.2023.112280. Epub 2023 Jun 8.

Authors

Jill B Harland¹, Subhra Samanta¹, Nicolai Lehnert²

Affiliations

¹ Department of Chemistry, The University of Michigan, Ann Arbor, MI 48109-1055, United States.
² Department of Chemistry, The University of Michigan, Ann Arbor, MI 48109-1055, United States. Electronic address: lehnertn@umich.edu.

PMID: 37352656
DOI: 10.1016/j.jinorgbio.2023.112280

Abstract

Bacterial NO Reductase (NorBC or cNOR) is a membrane-bound enzyme found in denitrifying bacteria that catalyzes the two-electron reduction of NO to N₂O and water. The mechanism by which NorBC operates is highly debated, due to the fact that this enzyme is difficult to work with, and no intermediates of the NO reduction reaction could have been identified so far. The unique active site of NorBC consists of a heme b₃/non-heme Fe_B diiron center. Synthetic model complexes provide the opportunity to obtain insight into possible mechanistic alternatives for this enzyme. In this paper, we present three new synthetic model systems for NorBC, consisting of a tetraphenylporphyrin-derivative clicked to modified BMPA-based ligands (BMPA = bis(methylpyridyl)amine) that model the non-heme site in the enzyme. These complexes have been characterized by EPR, IR and UV-Vis spectroscopy. The reactivity with NO was then investigated, and it was found that the complex with the BMPA-carboxylate ligand as the non-heme component has a very low affinity for NO at the non-heme iron site. If the carboxylate functional group is replaced with a phenolate or pyridine group, reactivity is restored and formation of a diiron dinitrosyl complex was observed. Upon one-electron reduction of the nitrosylated complexes, following the semireduced pathway for NO reduction, formation of dinitrosyl iron complexes (DNICs) was observed in all three cases, but no N₂O could be detected.

Keywords: Bacterial nitric oxide reductase; Click chemistry; Dinitrosyl iron complexes; Model complexes; Nitric oxide; Spectroscopy.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Bacteria / metabolism
Click Chemistry*
Heme / chemistry
Iron / chemistry
Nitric Oxide* / metabolism
Oxidation-Reduction

Substances

nitric-oxide reductase
Nitric Oxide
Iron
Heme