Iron-Ligand Structure and Iron Redox Property of Nitric Oxide Reductase Cytochrome P450nor from Fusarium oxysporum: Relevance to Its NO Reduction Activity

Abstract

We studied the nitric oxide reductase, cytochrome P450nor, purified from a denitrifying fungus Fusarium oxysporum with electron paramagnetic resonance spectral and redox potential measurements. The EPR spectral features of P450nor in the ferric resting, the ferric cyanide-bound, and the ferrous NO-bound forms were the same as the corresponding ones of other general P450s such as Pseudomonas putida P450cam. In contrast, the metyrapone complex of ferric P450nor gave an EPR spectrum with significantly different g values from that of P450cam. The EPR results were explained in terms of similarity in the immediate configuration of the S(-)-Fe-ligand (H2O, CN-, NO) structure between P450nor and P450cam but a structural difference at the heme distal pocket, especially in the substrate binding domain; P450cam has a camphor binding domain, while P450nor does not. In spite of the same S(-)-Fe-H2O configuration, the redox potential of P450nor in the ferric/ferrous couple was measured to be -307 mV, which is much lower than those of the camphor-bound (-140 mV) and -free (-250 mV) P450cam. The lower redox potential could be attributable to the different electrostatic interaction of the heme with its surroundings; e.g., the heme environment of P450nor is charged either more negatively or less positively than P450cam.(ABSTRACT TRUNCATED AT 250 WORDS)

Thiolate coordination to Fe(II)–porphyrin NO centers

“…This is further evidenced by comparison with the Fe(II)-NO adducts of P450nor, P450cam and P450 LM from Refs. [15,16]. The obtained g values as well as the observed 14 N hyperfine on g(mid) both resemble the properties of 1-MI as given in Table 1.…”

“…Scheme 1) and tetrahydrothiophene (a thioether) are presented in this study. The obtained data are correlated to the EPR spectra of 1 itself and of the corresponding adduct with 1-methylimidazole (1-MI) [21][22][23][24][25][26] as well as EPR data of NO adducts of ferrous P450 and P450nor [15,16]. Density functional (DFT) calculations on the simplified model [Fe(P)(SMe)(NO)] À (P = simplified Porphyrin ligand) are then used to explore the general properties of Fe(II)-NO complexes with trans S-donor ligands as they occur in the P450 enzymes (bacterial P450cam, liver microsomal P450 LM and P450nor) in detail.…”

“…Nevertheless, these systems are of great biological importance. NO bound heme centers with axial cysteinate coordination are present in fungal nitric oxide reductase (P450nor) [10][11][12][13][14][15][16] and nitric oxide synthase (NOS) [5]. Yoshimura studied the interaction of iron(II)-NO adducts with thiols and thioethers by EPR using protoporphyrin IX dimethylester as the porphyrin ligand [17].…”

Bioinspired electrocatalytic reduction of nitric oxide by immobilized heme groups

“…1). In comparison, the redox potentials at pH 7 of NO reducing enzymes such as cytochrome P450nor and cytochrome c nitrite reductase are À0.31 Vand À0.11 V versus SHE, respectively [36,37].…”

Dissimilatory Nitrite and Nitric Oxide Reductases

“…The redox potential of the enzyme (-307mV) is, however, about 60mV more negative than that of P450 cam . 130 Although the spectroscopic properties are unremarkable, the observed reactivity is quite unusual and offers substantial insight into the mechanism by which the enzyme reduces NO. The reaction catalyzed by P450 nor is shown in The enzyme is absolutely specific for NADH, showing no activity with NADPH.…”