DIRECT ELECTRON-TRANSFER REACTION OF HEMEPROTEINS PROMOTED BY METHYLENE-BLUE MODIFIED ELECTRODE

The heterogeneous electron transfer reaction of hemeproteins including hemoglobin, myoglobin and cytochrome C at Pt mesh electrode adsorbed methylene blue has been investigated. Thin-layer spectroelectrochemical technique was used for observing the electron transfer processes of three kinds of proteins, and the corresponding electrode rate constants were measured.

ELECTROCATALYSIS OF POLYPYRROLE-METHYLENE BLUE FILM MODIFIED ELECTRODE FOR DIRECT REDOX REACTION OF CYTOCHROME-C

The electron transfer process of hemeproteins on the electrode surface is considered a promising subject in the area of bioelectrochemistry. Electrochemists believe that electron transfer between electroactive proteins and electrode surface might be expected to simulate the electron transfer between proteins. This research provides information about the electron transfer mechanism in biological system. Cytochrome c is a typical electron transferring protein,

Heme oxygenase-1: a metabolic nike

SIGNIFICANCE: Heme degradation, which was described more than 30 years ago, is still very actively explored with many novel discoveries on its role in various disease models every year.

RECENT ADVANCES: The heme oxygenases (HO) are metabolic enzymes that utilize NADPH and oxygen to break apart the heme moiety liberating biliverdin (BV), carbon monoxide (CO), and iron. Heme that is derived from hemoproteins can be toxic to the cells and if not removed immediately, it causes cell apoptosis and local inflammation. Elimination of heme from the milieu enables generation of three products that influences numerous metabolic changes in the cell.

CRITICAL ISSUES: CO has profound effects on mitochondria and cellular respiration and other hemoproteins to which it can bind and affect their function, while BV and bilirubin (BR), the substrate and product of BV, reductase, respectively, are potent antioxidants. Sequestration of iron into ferritin and its recycling in the tissues is a part of the homeodynamic processes that control oxidation-reduction in cellular metabolism. Further, heme is an important component of a number of metabolic enzymes, and, therefore, HO-1 plays an important role in the modulation of cellular bioenergetics.

FUTURE DIRECTIONS: In this review, we describe the cross-talk between heme oxygenase-1 (HO-1) and its products with other metabolic pathways. HO-1, which we have labeled Nike, the goddess who personified victory, dictates triumph over pathophysiologic conditions, including diabetes, ischemia, and cancer.

Hydration-dependent conformational states of hemoglobin. Equilibrium and kinetic behavior

The equilibrium and kinetics of methemoglobin conversion to hemichrome induced by dehydration were investigated by visible absorption spectroscopy. Below about 0.20 g water per g hemoglobin only hemichrome was present in the sample; above this value, an increasing proportion of methemoglobin appeared with the increase in hydration. The transition between the two derivatives showed a time-dependent biphasic behavior and was observed to be reversible. The rates obtained for the transition of methemoglobin to hemichrome were 0.31 and 1.93 min-1 and for hemichrome to methemoglobin 0.05 and 0.47 min-1. We suggest that hemichrome is a reversible conformational state of hemoglobin and that the two rates observed for the transition between the two derivatives reflect the α- and β-chains of hemoglobin.

Alpha-glucosidase promotes hemozoin formation in a blood-sucking bug: An evolutionary history

Background: Hematophagous insects digest large amounts of host hemoglobin and release heme inside their guts. In Rhodnius prolixus, hemoglobin-derived heme is detoxified by biomineralization, forming hemozoin (Hz). Recently, the involvement of the R. prolixus perimicrovillar membranes in Hz formation was demonstrated. Methodology/Principal Findings: Hz formation activity of an α-glucosidase was investigated. Hz formation was inhibited by specific α-glucosidase inhibitors. Moreover, Hz formation was sensitive to inhibition by Diethypyrocarbonate, suggesting a critical role of histidine residues in enzyme activity. Additionally, a polyclonal antibody raised against a phytophagous insect α-glucosidase was able to inhibit Hz formation. The α-glucosidase inhibitors have had no effects when used 10 h after the start of reaction, suggesting that α-glucosidase should act in the nucleation step of Hz formation. Hz formation was seen to be dependent on the substrate-binding site of enzyme, in a way that maltose, an enzyme substrate, blocks such activity. dsRNA, constructed using the sequence of α-glucosidase gene, was injected into R. prolixus females' hemocoel. Gene silencing was accomplished by reduction of both α-glucosidase and Hz formation activities. Insects were fed on plasma or hemin-enriched plasma and gene expression and activity of α-glucosidase were higher in the plasma plus hemin-fed insects. The deduced amino acid sequence of α-glucosidase shows a high similarity to the insect α-glucosidases, with critical histidine and aspartic residues conserved among the enzymes. Conclusions/Significance: Herein the Hz formation is shown to be associated to an a-glucosidase, the biochemical marker from Hemipteran perimicrovillar membranes. Usually, these enzymes catalyze the hydrolysis of glycosidic bond. The results strongly suggest that α-glucosidase is responsible for Hz nucleation in the R. prolixus midgut, indicating that the plasticity of this enzyme may play an important role in conferring fitness to hemipteran hematophagy, for instance. © 2009 Mury et al.

Estudos bioquímicos de tegumento de soja brasileira: isolamento, purificação e caracterização de peroxidase com guaiacol como substrato

Pós-graduação em Biotecnologia - IQ

Identification of the overtone of the Fe-CO stretching mode in heme proteins: a probe of the heme active site.

Two CO-isotope sensitive lines have been detected in the overtone region of the resonance Raman spectra of CO-bound hemeproteins. One line is assigned as the overtone of the Fe-CO stretching mode and is located in the 1000- to 1070-cm-1 region. The other line is found in the 1180- to 1210-cm-1 region and is assigned as a combination between a porphyrin mode, nu 7, and the Fe-CO stretching mode. The high intensities of these lines, which in the terminal oxidase class of proteins are of the same order as those of the fundamental stretching mode, indicate that the mechanism of enhancement for modes involving the Fe-CO moiety is different from that for the modes of the porphyrin macrocycle and call for reexamination of Raman theory of porphyrins as applied to axial ligands. The anharmonicity of the electronic potential function was evaluated, revealing that in the terminal oxidases the anharmonicity is greater than in the other heme proteins that were examined, suggesting a distinctive interaction of the bound CO with its distal environment in this family. Furthermore, the anharmonicity correlates with the frequency of the C-O stretching mode, demonstrating that both of these parameters are sensitive to the Fe-CO bond energy. The overtone and combination lines involving the bound CO promise to be additional probes of heme protein structural properties.