In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 118, No. 21 ( 2021-05-25)
Abstract:
Nitric oxide (NO) reductase from the fungus Fusarium oxysporum is a P450-type enzyme (P450nor) that catalyzes the reduction of NO to nitrous oxide (N 2 O) in the global nitrogen cycle. In this enzymatic reaction, the heme-bound NO is activated by the direct hydride transfer from NADH to generate a short-lived intermediate ( I ), a key state to promote N–N bond formation and N–O bond cleavage. This study applied time-resolved (TR) techniques in conjunction with photolabile-caged NO to gain direct experimental results for the characterization of the coordination and electronic structures of I . TR freeze-trap crystallography using an X-ray free electron laser (XFEL) reveals highly bent Fe–NO coordination in I , with an elongated Fe–NO bond length (Fe–NO = 1.91 Å, Fe–N–O = 138°) in the absence of NAD + . TR-infrared (IR) spectroscopy detects the formation of I with an N–O stretching frequency of 1,290 cm −1 upon hydride transfer from NADH to the Fe 3+ –NO enzyme via the dissociation of NAD + from a transient state, with an N–O stretching of 1,330 cm −1 and a lifetime of ca. 16 ms. Quantum mechanics/molecular mechanics calculations, based on these crystallographic and IR spectroscopic results, demonstrate that the electronic structure of I is characterized by a singly protonated Fe 3+ –NHO •− radical. The current findings provide conclusive evidence for the N 2 O generation mechanism via a radical–radical coupling of the heme nitroxyl complex with the second NO molecule.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.2101481118
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2021
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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