Copper and manganese electron spin resonance studies of cytochrome c oxidase from Paracoccus denitrificans

The two-subunit cytochrome c oxidase from Paracoccus denitrificans contains two heme a groups and two copper atoms. However, when the enzyme is isolated from cells grown on a commonly employed medium, its electron paramagnetic resonance (EPR) spectrum reveals not only a Cu(II) powder pattern, but also a hyperfine pattern from tightly bound Mn(II). The pure Mn(II) spectrum is observed at ?40°C; the pure Cu(II) spectrum can be seen with cytochrome c oxidase from P. denitrificans cells that had been grown in a Mn(II)-depleted medium. This Cu(II) spectrum is very similar to that of cytochrome c oxidase from yeast or bovine heart. Manganese is apparently not an essential component of P. denitrificans cytochrome c oxidase since it is present in substoichiometric amounts relative to copper or heme a and since the manganese-free enzyme retains essentially full activity in oxidizing ferrocytochrome c. However, the manganese is not removed by EDTA and its EPR spectrum responds to the oxidation state of the oxidase. In contrast, manganese added to the yeast oxidase or to the manganese-free P. denitrificans enzyme can be removed by EDTA and does not respond to the oxidation state of the enzyme. This suggests that the manganese normally associated with P. denitrificans cytochrome c oxidase is incorporated into one or more internal sites during the biogenesis of the enzyme.     

Mitochondrial biogenesis during fungal spore germination. Development of cytochrome c oxidase activity.

Mitochondria from dormant spores of the fungus Botryodiplodia theobromae did not contain extractable cyctochrome c oxidase (EC 1.9.3.1) activity; however, this enzyme activity was elaborated rapidly after 150 min of the 240-min germination sequence. The absence of cytochrome c oxidase activity in the dormant spores apparently is not an artifact caused by spore disruption and fractionation procedures, transient enzyme instability, or insensitivity of the enzyme assay. Mitochondria from dormant spores of three other phylogenetically diverse genera of fungi were observed to contain readily detectable quantities of cytochrome c oxidase, suggesting that the absence of the enzyme in B. theobromae may be relatively novel. The elaboration of cytochrome c oxidase activity in germinating spores was abolished by cycloheximide if the drug was added at or before 95 min of germination, but development of enzyme activity was initially insensitive to inhibitors of the mitochondrial genetic system, chloramphenicol or ethidium bromide. Incubation of spores in both ethionine and S-2-aminoethyl-l-cysteine reduced the amount of extracted cytochrome c oxidase activity. Elaboration of enzyme activity was severely retarded by cerulenin, an inhibitor of fatty acid biosynthesis and of spore germination. This enzyme activity developed in water-incubated or 1% Tween 80-incubated spores in which only the cytoplasmic ribosomes are functional in translation of a stored nuclear messenger RNA. The results of this study show that cytoplasmic (but not mitochondrial) ribosome function is required for development of this enzyme activity during spore germination, and they suggest that a portion of the cytochrome c oxidase enzyme or some other protein required for its activity is synthesized de novo upon germination.     

Nucleotide sequence of the gene for monoamine oxidase (maoA) from Escherichia coli

We found that the structural gene for monoamine oxidase was located at 30.9 min on the Escherichia coli chromosome. Deletion analysis showed that two amine oxidase genes are located in this region. The nucleotide sequence of one of the two genes was determined. The peptide sequence of the first 40 amino acids from the N terminus of monoamine oxidase purified from E. coli agrees with that deduced from the nucleotide sequence of the gene. The leader peptide extends over 30 amino acids. The nucleotide sequence of the gene and amino acid sequence of the predicted mature enzyme (M.W. 81,295) were highly homologous to those of the maoA_K gene and monoamine oxidase from Klebsiella aerogenes, respectively. From these results and analysis of the enzyme activity, we concluded that the gene encodes for monoamine oxidase (maoA_E). The tyrosyl residue, which may be converted to topa quinone in the E. coli enzyme, was located by comparison with amino acid sequences at the cofactor sites in other copper/topa quinone-containing amine oxidases.     

Molecular structure and subcellular localization of spinach leaf glycolate oxidase

Glycolate oxidase (E.C. 1.1.3.1) was purified from spinach leaves (Spinacia oleracea). The molecular weight of the native protein was determined by sucrose density gradient centrifugation to be 290,000 daltons (13S), whereas that of the monomeric form was 37,000 daltons. The quaternary structure of the holoenzyme is likely to be octameric, analogous to pumpkin cotyledon glycolate oxidase [Nishimura et al, 1982]. The subcellular localization of the enzyme was studied using linear sucrose density gradient centrifugation, and it was found that glycolate oxidase activity is detectable in both leaf peroxisomal and supernatant fractions, but not in chloroplasts and mitochondria; the activity distribution pattern is essentially similar to that for catalase, a known leaf peroxisomal enzyme. Ouchterlony double diffusion and immunotitration analyses, demontrated that the rabbit antiserum against purified spinach leaf glycolate oxidase cross-reacted, identically, with the enzyme molecules present in two different subcellular fractions, i.e, the leaf peroxisome and supernatant fractions. It is thus concluded that the enzyme present in the supernatant is due to the disruption of leaf peroxisomes during the isolation, and hence glycolate oxidase is exclusively localized in leaf peroxisomes in spinach leaves.     

Molecular structure and subcellular localization of spinach leaf glycolate oxidase

Glycolate oxidase (E.C. 1.1.3.1) was purified from spinach leaves (Spinacia oleracea). The molecular weight of the native protein was determined by sucrose density gradient centrifugation to be 290,000 daltons (13S), whereas that of the monomeric form was 37,000 daltons. The quaternary structure of the holoenzyme is likely to be octameric, analogous to pumpkin cotyledon glycolate oxidase [Nishimura et al, 1982]. The subcellular localization of the enzyme was studied using linear sucrose density gradient centrifugation, and it was found that glycolate oxidase activity is detectable in both leaf peroxisomal and supernatant fractions, but not in chloroplasts and mitochondria; the activity distribution pattern is essentially similar to that for catalase, a known leaf peroxisomal enzyme. Ouchterlony double diffusion and immunotitration analyses, demonstrated that the rabbit antiserum against purified spinach leaf glycolate oxidase cross-reacted, identically, with the enzyme molecules present in two different subcellular fractions, i.e, the leaf peroxisome and supernatant fractions. It is thus concluded that the enzyme present in the supernatant is due to the disruption of leaf peroxisomes during the isolation, and hence glycolate oxidase is exclusively localized in leaf peroxisomes in spinach leaves.     

Transient Binding of CO to CuB in Cytochrome c Oxidase Is Dynamically Linked to Structural Changes around a Carboxyl Group: A Time-Resolved Step-Scan Fourier Transform Infrared Investigation

The redox-driven proton pump cytochrome c oxidase is that enzymatic machinery of the respiratory chain that transfers electrons from cytochrome c to molecular oxygen and thereby splits molecular oxygen to form water. To investigate the reaction mechanism of cytochrome c oxidase on the single vibrational level, we used time-resolved step-scan Fourier transform infrared spectroscopy and studied the dynamics of the reduced enzyme after photodissociation of bound carbon monoxide across the midinfrared range (2300-950 cm⁻¹). Difference spectra of the bovine complex were obtained at -20°C with 5 μs time resolution. The data demonstrate a dynamic link between the transient binding of CO to Cu_B and changes in hydrogen bonding at the functionally important residue E(I-286). Variation of the pH revealed that the pK_a of E(I-286) is >9.3 in the fully reduced CO-bound oxidase. Difference spectra of cytochrome c oxidase from beef heart are compared with those of the oxidase isolated from Rhodobacter sphaeroides. The bacterial enzyme does not show the environmental change in the vicinity of E(I-286) upon CO dissociation. The characteristic band shape appears, however, in redox-induced difference spectra of the bacterial enzyme but is absent in redox-induced difference spectra of mammalian enzyme. In conclusion, it is demonstrated that the dynamics of a large protein complex such as cytochrome c oxidase can be resolved on the single vibrational level with microsecond Fourier transform infrared spectroscopy. The applied methodology provides the basis for future investigations of the physiological reaction steps of this important enzyme.     

Abscisic Aldehyde Is an Intermediate in the Enzymatic Conversion of Xanthoxin to Abscisic Acid in Phaseolus vulgaris L. Leaves

The enzymatic conversion of xanthoxin to abscisic acid by cell-free extracts of Phaseolus vulgaris L. leaves has been found to be a two-step reaction catalyzed by two different enzymes. Xanthoxin was first converted to abscisic aldehyde followed by conversion of the latter to abscisic acid. The enzyme activity catalyzing the synthesis of abscisic aldehyde from xanthoxin (xanthoxin oxidase) was present in cell-free leaf extracts from both wild type and the abscisic acid-deficient molybdopterin cofactor mutant, Az34 (nar2a) of Hordeum vulgare L. However, the enzyme activity catalyzing the synthesis of abscisic acid from abscisic aldehyde (abscisic aldehyde oxidase) was present only in extracts of the wild type and no activity could be detected in either turgid or water stressed leaf extracts of the Az34 mutant. Furthermore, the wilty tomato mutants, sitiens and flacca, which do not accumulate abscisic acid in response to water stress, have been shown to lack abscisic aldehyde oxidase activity. When this enzyme fraction was isolated from leaf extracts of P. vulgaris L. and added to extracts prepared from sitiens and flacca, xanthoxin was converted to abscisic acid. Abscisic aldehyde oxidase has been purified about 145-fold from P. vulgaris L. leaves. It exhibited optimum catalytic activity at pH 7.25 in potassium phosphate buffer.     

The biochemistry of HEXA and HEXB gene mutations causing GM2 gangliosidosis

Immuno-flow cytometry was tested as a tool to estimate the cellular concentration of mitochondrial proteins in cultured cells, using cytochrome c oxidase as a model enzyme. Cells labelled with antibodies against cytochrome c oxidase, in which the amount of the enzyme was reduced by various extents, showed a linear relationship between the size of the signal obtained by immuno-flow cytometry and the amount of the enzyme. The determination by immuno-flow cytometry resulted in data comparable to the results obtained by immunoprecipitation and activity measurement. Since immuno-flow cytometry requires only limited numbers of cells, the method could especially be of value for diagnostic purposes. This is illustrated by the results obtained by comparing activity measurements and immuno-flow cytometry in the initial screening of cell lines derived from patients with deficiencies in the activity of cytochrome c oxidase.     

Characterization of cholesterol oxidase from a marine Streptomyces sp. and its cytotoxicity

A marine actinobacterial strain (designated as AKHSS) capable of producing cholesterol oxidase on the enzyme indicator plates was identified as Streptomyces sp. The cell-free lysate of the strain was used for monitoring the production of cholesterol oxidase and the maximal enzyme yields were recorded at 72 h post inoculation. The cholesterol oxidase was purified using polyethylene glycol 4000 precipitation, diethylaminoethyl Sephacel anionic column chromatography and Superdex-200 gel filtration to near homogeneity. Through electron-spray ionization mass spectrometry, molecular mass of the purified enzyme was recorded as 42.84 kDa. The optimum pH of the enzyme was found to be 9 and it was stable up to 60 °C. Metal salts like MgSO₄ and ZnSO₄ stimulated the enzyme activity. The V_max and K_m of the purified enzyme with cholesterol as substrate were found to be 1.22 μmoles/min/mL and 0.54 mM respectively. The enzyme showed significant cytotoxicity on breast (MCF-7), nasopharyngeal (KB) and ovarian (OVCAR) cancer cell lines at very low concentrations ranging from 0.093 to 0.14 μM, as evident from MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] cell viability assay. Besides, the enzyme exhibited relatively less cytotoxicity on primary mouse embryonic fibroblast (3T3) cells. Thus, cholesterol oxidase of Streptomyces sp. AKHSS could be a potential anticancer agent.     

Separate monophenolase and o-diphenolase enzymes in Triticum aestivum

Monophenolase and o-diphenolase activities of polyphenol oxidase are usually thought to be a part of the same enzyme complex. It has now been demonstrated that the two catalytic activities of the polyphenol oxidase of wheat grains are separable and reside in different enzymes. The electrophoretically separated monophenolase enzyme showed specificity only for monophenol (l-tyrosine) after its elution from acrylamide gels. Further, this enzyme is confined to the endosperm tissue and is undetectable in the embryonic region of the seedling.     

IAA Oxidase Inhibitors from Normal and Mutant Maize Plants

Extracts of maize (Zea mays L.) plants contain substances which, in vitro, inhibit an indoleacetic acid (IAA) oxidase enzyme from maize. The extracts can be freed of inhibitors by dialysis or by passage through columns of polyvinylpyrrolidone powder. Inhibitor-free extracts contain an IAA oxidase enzyme which requires a phenolic co-factor and is stimulated by Mn²⁺.     

Marked increase in ascorbate oxidase protein in pumpkin callus by adding copper

Ascorbate oxidase from pumpkin (Cucurbita sp.) was purified from a commercially available preparation. A single polypeptide band with M_r 64,000 was detected after sodium dodecylsulfate-polyacrylamide gel electrophoresis of the purified enzyme. In double immunodiffusion tests, antiserum against the purified preparation formed a single precipitin line with the crude extract from pumpkin fruit tissue or the callus as well as with the purified preparation. Immunological blotting method showed that mol wt of ascorbate oxidase subunit in pumpkin callus was the same as that of the purified preparation. Analysis with the single radial immunodiffusion method showed that the increase in ascorbate oxidase activity during the growth of pumpkin callus correlated with an increase in the enzyme protein. Furthermore, enzyme protein in the callus grown in the presence of 10 micromolar CuSO₄ for 2 weeks was about eight times that grown in the presence of 0.1 micromolar CuSO₄. The synthesis of ascorbate oxidase in pumpkin callus may be induced by copper, a prosthetic metal of the enzyme, or copper may help stabilize the enzyme against proteolytic breakdown.     

Particulate and soluble forms of o-diphenol oxidase from potato tubers

A soluble and two different particulate forms of o-diphenol oxidase have been obtained from aged or fresh potato slices by differential and density gradient centrifugation. The particulate enzymes were shown to sediment with microsomes and peroxisomes, respectively. Over half the enzyme activity of aged slices was found to be particle bound, with approximately twice as much enzyme in the microsomes as in the peroxisomal fraction. Very similar distribution patterns have been obtained with fresh potatoes, which have an o-diphenol oxidase activity approximately one-third that of aged slices.     

Early changes in mitochondrial monoamine oxidase activity of rat liver during 2-acetylaminofluorene feeding

The activities of mitochondrial type A and B monoamine oxidase were determined in the liver of rats fed a diet containing 2-acetylaminofluorene (AAF). Three days after the initiation of AAF-feeding, there was a significant decrease of type B monoamine oxidase activity without affect on type A enzyme. The decreased activity of type B monoamine oxidase, which reached a minimum after three weeks, was sustained for as long as AAF-feeding was continued. Sex-related difference in response to AAF was seen in the rat with respect to the onset and the intensity of the decreased type B monoamine oxidase activity, male rats being more sensitive to the carcinogen than female rats. In contrast to the in vivo effect, AAF showed a potent inhibitory effect on type A monoamine oxidase, rather than on type B enzyme, when added in vitro. The pI₅₀ values were estimated to be 7.5 against type A monoamine oxidase and 4.1 against type B enzyme, respectively. The in vitro inhibition of both types of monoamine oxidase by AAF was competitive. The K_i values for AAF were calculated to be 9.51 · 10^?9 M for type A monoamine oxidase and 1.30 · 10^?5 M for type B enzyme, respectively. In accordance with the potent inhibitory effect of AAF on type A monoamine oxidase in vitro, a single administration of the carcinogen, at a dose of 50 mg/kg, resulted in a marked and temporal decrease of the enzyme activity in the mitochondria of male rat liver. Recovery of the decreased type B monoamine oxidase activity was slow, and the enzyme activity did not return to control levels, even if rats were fed the basal diet for 2 or 4 weeks after the cessation of AAF-feeding.     

Phenol oxidase in the blood cells of millipedes

The nature and properties of the phenol oxidase present in the blood cells and plasma of three species of millipedes, Thyropygus poseidon, Polydesmus species, and Spirostreptus asthenus, have been investigated using a number of substrates as well as activators and inhibitors. The enzyme is located in the granular haemocytes. In the in situ condition it oxidizes diphenols, polyphenols, and also tyrosine. But when extracted from the homogenate of blood cells it showed only diphenolase activity. There is evidence of phenol oxidase activity in the plasma, but it did not act on tyrosine. The results obtained have been discussed in the light of previous work. It is suggested that the cell enzyme may have two sites of activity responsible for the oxidation of diphenol and also tyrosine. The observation that the monophenol oxidase activity is absent when the enzyme is extracted and isolated suggests that one of the sites of activity of the enzyme may be destroyed in the process of extraction.     

Indoleacetic Acid Oxidase: A Dual Catalytic Enzyme?

The isolation of a unique enzyme capable of oxidizing indoleacetic acid, but devoid of peroxidase activity, has been reported for preparations from tobacco roots and commercial horseradish peroxidase. Experiments were made to verify these results using enzyme obtained from Betula leaves and commercial horseradish peroxidase. Both indoleacetic acid oxidase and guaiacol peroxidase activity appeared at 2.5 elution volumes from sulfoethyl-Sephadex. These results were obtained with both sources of enzyme. In no case was a separate peak of indoleacetic acid oxidase activity obtained at 5.4 elution volumes as reported for the tobacco enzyme using the same chromatographic system. Both types of activity, from both sources of enzyme, also eluted together during gel filtration. Successful column chromatography of Betula enzyme was dependent upon previous purification by membrane ultrafiltration. These results indicate indoleacetic acid oxidase activity and guaiacol peroxidase activity are dual catalytic functions of a single enzyme.     

A simple purification procedure of D-amino-acid oxidase from <Emphasis Type="Italic">Candida guilliermondii</Emphasis>

D-amino-acid oxidase (EC 1.4.3.3) was purified about 1480-fold from the yeast Candida guilliermondii using chromatofocusing method. The purification procedure gave an enzyme preparation which is greater than 90% homogenous on SDS-polyacrylamide gels with a specific activity of 11.54 U/mg at 30°C with D-proline as substrate with the yield of total activity 9.3%. The molecular weights of subunit and native enzyme were determined to be 38.4 and 78.6 kDa by SDS-polyacrylamide gel electrophoresis and gel-filtration, respectively, suggesting that the native enzyme exists as a homodimer. A single molecular form with an isoelectric point of 6.85 was detected in analytical isoelectrofocusing. The optimum pH and temperature were 8.0 and 33°C. An enzyme shows stability in the pH range from 7.4 to 9.0 and at the temperature no higher than 38°C. Activation energy for D-amino-acid oxidase reaction was calculated to be 60 kJ/mol at 30°C. The strict D-isomer specificity of the enzyme is confirmed, since no reaction could be detected with L-amino acids, and a large number of D-amino acids could be substrates for this enzyme. K _m and V _max values were determined for D-proline and D-alanine, which, among 22 tested, were the best substrates of the enzyme. D-amino-acid oxidase from the yeast C. guilliermondii is a flavoprotein oxidase in which the prosthetic group is tightly, but not covalently, bound FAD. The enzyme is completely inhibited by sodium benzoate, SH-oxidizing agents, but not by sodium azide, toluene or chloroform.     

Heterogeneity of hepatic nicotine oxidase

When rats were pretreated with 3-methylcholanthrene or β-naphthoflavone, hepatic nicotine oxidase activity per cytochrome P-448 molecule decreased, but the specific activity of the enzyme remained unchanged. After phenobarbital pretreatment, the specific activity of nicotine oxidase increased while the activity of the enzyme per cytochrome P-450 molecule decreased. α-Naphthoflavone selectively inhibited the activities of phenobarbital-induced nicotine oxidase and constitutive form(s) of the enzyme. These results show that phenobarbital-induced cytochrome P-450 and constitutive forms(s) of the enzyme may be active in hepatic nicotine oxidation.     

The effects of reversible freezing inactivation and inhibitor binding on redox properties of l-amino-acid oxidase

We measured the redox potentials of frozen inactivated l-amino-acid oxidase (l-amino-acid:oxygen oxidoreductase (deaminating), EC 1.4.3.2) and inhibitor-bound (anthranilic acid) enzyme, and compared these redox properties to those of active l-amino-acid oxidase and benzoate-bound d-amino-acid oxidase (EC 1.4.3.3), respectively. The redox properties of the inactive enzyme are similar to the properties of free flavin; the potential is within 0.015 V of free flavin and no radical stabilization is seen. This corresponds to the loss of most interactions between apoprotein and flavin. In contrast, the anthranilic acid lowers the amount of radical stabilized from 85% to 35%. The potentials are still 0.150 V positive of free flavin, indicating that in the presence of inhibitor, many flavin-protein interactions remain intact. The difference between this behavior and that of d-amino-acid oxidase bound to benzoate, where the amount of radical declined from 95% to 5%, is explained on the basis of the relative tightness of binding of apoprotein to FAD. d-Amino-acid oxidase apoprotein has a relatively low K_a (10⁶) for FAD, and benzoate has a relatively high K_a (10⁵) for the enzyme. Therefore, the binding of benzoate increases the tightness of FAD binding to apo-d-amino-acid oxidase (10¹¹), indicating significant changes in flavin-protein interactions. In contrast, apo-l-amino-acid oxidase binds flavin tightly (the K_a is greater than 10⁷) and the enzyme binds to anthranilate much less tightly, with a K_a of 10³. The l-amino-acid oxidase apoprotein binding to FAD is tight initially, and the binding of anthranilate changes it only slightly. Therefore, redox studies indicate that the ability of a flavoprotein to be regulated may be influenced by the strength of the interaction of flavin with the apoprotein, as well as the strength of interaction of the substrate or activator.     

Aldehyde oxidase activity in the tumorous-head strain of Drosophila melanogaster

Gross aldehyde oxidase activity from the egg-stage through 10-day-old adults and distribution of the enzyme in eye-antennal imaginal discs in third instar larvae were determined for the tumorous-head strain of Drosophila melanogaster. Aldehyde oxidase activity of several laboratory strains was measured for comparative purposes. Aldehyde oxidase activity was 100% higher during embryogenesis in tuh(ASU) eggs than in Oregon-R-C eggs. A second period of elevated aldehyde oxidase activity was observed during metamorphosis where tuh(ASU) pupae averaged 65% more enzyme activity than Oregon-R-C. Therefore, during determination and differentiation of the eye-antennal imaginal disc, the tuh(ASU) strain possesses a high aldehyde oxidase activity. Wild-type Drosophila melanogaster antennal imaginal discs are aldehyde oxidase positive, whereas attached eye imaginal discs are apparently aldehyde oxidase negative. A sample of eye-antennal imaginal discs from tuh(ASU) third instar larvae revealed that either one or both eye discs of 64% of the larvae were aldehyde oxidase positive. Aldehyde oxidase activity may be correlated with the homoeotic transformation in parts of the eye disc.