Electron paramagnetic resonance spectra of catalase in mammalian tissues

Classical catalase: ancient and modern

This review describes the historical difficulties in devising a kinetically satisfactory mechanism for the classical catalase after its identification as a unique catalytic entity in 1902 and prior to the breakthrough 1947 analysis by Chance and co-workers which led to the identification of peroxide compounds I and II. The role of protons in the formation of these two ferryl complexes is discussed and current problems of inhibitory ligand and hydrogen donor binding at the active site are outlined, especially the multiple roles involving formate or formic acid. A previous mechanism of NADPH-dependent catalase protection against substrate inhibition is defended. A revised model linking the catalytic ('catalatic') action and the one-electron side reactions involving compound II is suggested. And it is concluded that, contrary to an idea proposed in 1963 that eukaryotic catalase might be a 'fossil enzyme', current thinking gives it a central role in the redox protective processes of long term importance for human and other eukaryotic and prokaryotic life.

Mitochondrial dysfunction in patients with severe sepsis: An EPR interrogation of individual respiratory chain components

Electron paramagnetic resonance (EPR) spectra of complex biological systems contain information about the paramagnetic centres present. Retrieving such information is important since paramagnetic species are common intermediates of all redox reactions in both normal and abnormal metabolism. However, it is often difficult to determine the nature and content of all paramagnetic species present because the EPR signals from individual centres overlap. Here, we apply our deconvolution method based on spectra subtraction with variable coefficient to quantify individual paramagnetic components of human muscle biopsies taken from critically ill patients with severe sepsis. We use low temperature EPR spectroscopy to identify and quantify nine different paramagnetic species in the tissue. These include the majority of the mitochondrial iron-sulfur centres and the first in vivo report of a mitochondrial radical assigned to a spin-coupled pair of semiquinones (SQ*-SQ*). We have previously demonstrated in these same muscle biopsies that biochemical assays of mitochondrial dysfunction correlate with clinical outcomes (D. Brealey, M. Brand, I. Hargreaves, S. Heales, J. Land, R. Smolenski, N.A. Davies, C.E. Cooper, M. Singer, Association between mitochondrial dysfunction and severity and outcome of septic shock. Lancet 360 (2002) 219-223.). Analysis of the paramagnetic centres in the muscle confirms and extends these findings: the (SQ*-SQ*) radical species negatively correlates with the illness severity of the patient (APACHE II score) and a decreased concentration of mitochondrial Complex I iron-sulfur redox centres is linked to mortality.

Catalase depression in malignant liver from chickens with myeloblastosis and Marek's disease

In rapidly frozen livers from chickens affected with myeloblastosis and Marek's disease and from unaffected control birds there exists a strong correlation between catalase activity and catalase Electron Paramagnetic Resonance (EPR) signal intensities. The diseased chickens had activities and signals reduced to as little as 10% of control values. There were no changes in the EPR parameters in diseased liver and the data support the hypothesis that the lowering in activity is due to lowered catalase levels rather than to catalase inhibition. The rate of transformation of catalase to catalase-formate in liver was studied by freeze-clamping liver in anaesthetised chickens, then warming to 37 degrees for 1 or 2 minutes anaerobiosis, and then refreezing. The only difference of significance in this transformation between diseased and normal livers was the greater percentage of total catalase present as catalase-formate (approximately + 15%) in aerobic diseased liver, which may indicate a lowered production of hydrogen peroxide, relative to formate, in these livers. The rate of transformation was far faster in chickens (t1/2 less than 1 min) than in the rat (t1/2 = 7.7 min).

Characterization of the peroxidase in human eosinophils

1. Human eosinophils contain a peroxidase that appears to be of the same type as horseradish peroxidase, lactoperoxidase and intestine peroxidase. 2. Electron paramagnetic resonance spectra of human eosinophils show high-spin ferric heme signals with rhombic symmetry (gx = 6.56, gy = 5.31 and gx = 6.33, gy = 5.59) for the heme group. Part of the more rhombic signal is due to catalase, whereas the other part is completely due to the peroxidase. In addition to these high-spin heme compounds a low-spin heme compound is detectable with g values (gx = 3.09, gy = 2.22 and gz = 1.48) characteristic of a bisimidazole heme iron complex. 3. The amount of heme iron derived from the eosinophil peroxidase, determined from electron paramagnetic spectra, is 13.2 X 10(-17) mol/eosinophil. This is in good agreement with the pyridine hemochrome spectra which yield a value of 13.5 X 20(-17) mol heme iron/eosinophil.

Magnetic circular dichroism studies of bovine liver catalase

Absorption, circular dichroism (CD) and magnetic circular dichroism (MCD) spectra of beef liver catalase at pH 5.0 and 6.9, and its complexes with NaF, KCNO, NaCNS, NaN3 and NaCN, have been measured between 250 nm and 700 nm at room temperature. The pH 6.9 native catalase MCD shows the presence of several additional transitions not resolved in the absorption spectrum. While these bands can be seen in the spectra of all the derivatives, with the exception of the cyanide, their relative intensities changes considerably between complexes. Of special interest in the MCD of ferric hemes is the signal intensity at about 400 nm and 620 nm. The data indicate that the MCD intensity at 620 nm increases as the high spin iron porphyrin fraction increases, reaching a maximum with the fluoride complex. The 430 nm band intensity increases as the proportion of low spin iron increases, reaching a maximum with the cyanide complex. The MCD spectra also indicate clearly the existence of spin mixtures in the complexes with CNO-, CNS-, and N3-, where both the 430 nm and 620 nm bands have appreciable intensity. It is significant that despite almost identical absorption spectra the CNS- complex has higher fraction of low spin iron than either the CNO- or the N3- species. The differences between the pH 5 and 6.9 MCD spectra of the native catalase suggest that the environment of the heme centre is sensitive to protonation.

Effect of pH on bovine liver catalase as determined by electron paramagnetic resonance

Two major rhombic high-spin ferric heme signals are observed during the pH titration of bovine liver catalase. The less rhombic signal if dominant above pH 6.0 and the more rhombic signal below pH 6.0. Ethanol in high concentration enhances the relative intensity of the less rhombic signal. These data demonstrate the sensitivitiy of the ligand field to changes in catalase solvent and, furthermore, suggest that both rhombic configuration posses identical spectral and catalytic properties.