Cytochrome P460 Cofactor Maturation Involves a Peroxide- Dependent Post-Translational Modification

Cytochrome P460s are heme enzymes that oxidize hydroxylamine to nitrous oxide as part of the biogeochemical nitrogen cycle. They bear unique “heme P460” cofactors that are cross-linked to their host polypeptides by a post-translationally modified lysine residue. Wild-type N. europaea cytochrome P460 may be isolated as a cross-link deficient proenzyme following anaerobic overexpression in E. coli. When treated with peroxide, This proenzyme undergoes complete maturation to active enzyme with spectroscopic properties that match wild-type cyt P460. Together, these data indicate that the cofactor is primed to undergo this covalent modification by virtue of the protein fold. A putative mechanism analogous to that used by heme oxygenases to degrade hemes is proposed.

Non-enzymatic degradation of carbon nanotubes in the presence of bacterial enzymes

The enzymatic degradation of carbon nanotubes (CNTs) by several enzymes has been reported. However, because organisms that possess these enzymes have limited habitats and distribution areas, it is unclear whether CNTs can be degraded in the general environment. The investigation of CNTs degradation by enzymes derived from bacteria, which inhabit a wide range of environments and have diverse metabolic systems, is inevitable for predicting the environmental fate of CNTs. In this study, the degradation of oxidized (carboxylated) single-walled CNTs (O-SWCNTs) by mt2DyP, a dye-decolorizing peroxidase of Pseudomonas putida mt-2, a common soil bacterium, was investigated. Suspensions of O-SWCNTs gradually became transparent and their optical absorbance decreased during 30 d of incubation in the presence of mt2DyP produced by a recombinant Brevibacillus choshinensis strain and its substrate, H2O2. The degradation was enhanced by higher H2O2 concentrations. The measurement of Raman spectra revealed the complete degradation of O-SWCNTs after 30 d of incubation with 100 mM H2O2. However, surprisingly, this heme enzyme was inactivated within 60 min of the incubation with O-SWCNTs, which suggested that the degradation of O-SWCNTs was not catalyzed by the enzyme. The inactivation of mt2DyP was accompanied by the release of iron, which suggested that the degradation of the O-SWCNTs was owing to the Fenton reaction caused by the iron released from mt2DyP and the supplied H2O2. A chelating agent, diethylenetriaminepentaacetic acid, significantly inhibited the O-SWCNTs degradation, proving the degradation by the Fenton reaction. These phenomena were also observed with another heme enzyme, Cytochrome P450. These results are important for predicting the fate of CNTs in a wide range of environments, as heme enzymes are secreted by many bacteria in the environment. This study also shows that the effect of the Fenton reaction should be considered to validate the degradation of CNTs by heme enzymes.

Electrocatalysis by Heme Enzymes—Applications in Biosensing

Heme proteins take part in a number of fundamental biological processes, including oxygen transport and storage, electron transfer, catalysis and signal transduction. The redox chemistry of the heme iron and the biochemical diversity of heme proteins have led to the development of a plethora of biotechnological applications. This work focuses on biosensing devices based on heme proteins, in which they are electronically coupled to an electrode and their activity is determined through the measurement of catalytic currents in the presence of substrate, i.e., the target analyte of the biosensor. After an overview of the main concepts of amperometric biosensors, we address transduction schemes, protein immobilization strategies, and the performance of devices that explore reactions of heme biocatalysts, including peroxidase, cytochrome P450, catalase, nitrite reductase, cytochrome c oxidase, cytochrome c and derived microperoxidases, hemoglobin, and myoglobin. We further discuss how structural information about immobilized heme proteins can lead to rational design of biosensing devices, ensuring insights into their efficiency and long-term stability.

A Computational Approach to Understand the Role of Metals and Axial Ligands in Artificial Heme Enzymes Catalyzed C-H Insertion

Engineered heme enzymes such as myoglobin and cytochrome P450s metalloproteins are gaining widespread importance due to their efficiency in catalyzing non-natural reactions. In a recent strategy, the naturally occurring Fe...

Single Gold Nanoparticle-driven Heme Cofactor Nanozyme as Unprecedented Oxidase Mimetic

The catalytic diversity of heme enzymes is a perpetuating pursuit for biomimetic chemistry, but heme nanozymes exhibit catalytic activity only reminiscent of peroxidases. Miraculously, the oxidase-like catalytic function of heme...