Studies on the bacterial hemoglobin from Vitreoscilla. Redox properties and spectroscopic characterization of the different forms of the hemoprotein.
Vitreoscilla contained a homodimeric bacterial hemoglobin (VtHb). The purification of this protein yielded VtmetHb which exhibited electronic and electron paramagnetic resonance (EPR) spectra, showing that it existed predominantly in a high-spin ferric form, both axial and rhombic components being present. The preparations also contained variable amounts of low-spin components. There was no evidence that these high-spin and low-spin forms were in equilibrium. The former were reducible by NADH catalyzed by the NADH-metVtHb reductase, and the latter were not. High ionic strength and high pH led to the formation of low-spin metVtHb; both treatments were reversible. Cyanide and imidazole liganded to VtHb resulted in the conversion of high-spin to low-spin ferric heme centers, each with characteristic electronic and EPR spectra. Some preparations of VtHb exhibited EPR signals consistent with a sulfur ligand bound to the ferric site. When VtHb was treated with NADH plus the reductase in the presence of oxygen, the intensity of the high-spin EPR signals decreased significantly. No reduction occurred in the absence of oxygen, suggesting a possible role for the superoxide anion. Dithionite treatment of VtHb resulted in a slow reduction, but the main product of the reaction of dithionite-reduced VtHb with oxygen was VtmetHb, not VtHbO2. EPR spectra of whole cells of Vitreoscilla exhibited a variety of intense signals at low and high magnetic field, the g-values being consistent with the presence of high-spin ferric heme proteins, in addition to an iron-containing superoxide dismutase (FeSOD) and iron-sulfur proteins. EPR spectra of the cytosol fraction of Vitreoscilla showed the expected resonances for VtmetHb and FeSOD.
Kroneck
P M
PM
Fakultät für Biologie, Universität Konstanz, Federal Republic of Germany.
Jakob
W
W
Webster
D A
DA
DeMaio
R
R
D001426:Bacterial Proteins / Q000032:analysis*; D002462:Cell Membrane / Q000502:physiology; D003593:Cytoplasm / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D006454:Hemoglobins / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D041962:Thiotrichaceae / Q000032:analysis*
D001426:Bacterial Proteins; D006454:Hemoglobins; D008024:Ligands