Contributions of EPR spectroscopy to our knowledge of oxidative enzymes

Impact of seed color and storage time on the radish seed germination and sprout growth in plasma agriculture

The use of low-temperature plasma for the pre-sowing seed treatment is still in the early stage of research; thus, numerous factors affecting germination percentage, seedling growth, and yield remains unknown. This study aimed to estimate how two critical factors, such as harvest year and seed coat color, affect the percentage of germination and seedling growth after plasma treatment. Radish seeds stored for 2 and 1 year after harvesting (harvested in 2017 and 2018) were sorted into two colors (brown and grey) to investigate the plasma effect on harvest year and seed coat color. We analyzed the amounts of seed phytohormones and antioxidant (γ-tocopherol) were analyzed using mass spectrometry, and physical changes were studied using SEM, EDX, and EPR to understand the mechanism of plasma-induced changes in radish seeds. The obtained results revealed that plasma treatment on seeds affects the germination kinetics, and the maximal germination percentage depends on seed color and the time of seed storage after harvest. Through this study, for the first time, we demonstrated that physical and chemical changes in radish seeds after plasma treatment depends upon the seed color and harvest year. Positive effects of plasma treatment on growth are stronger for sprouts from seeds harvested in 2017 than in 2018. The plasma treatment effect on the sprouts germinated from grey seeds effect was stronger than sprouts from brown radish seeds. The amounts of gibberellin A3 and abscisic acid in control seeds strongly depended on the seed color, and plasma induced changes were better in grey seeds harvested in 2017. Therefore, this study reveals that Air scalar-DBD plasma's reactive oxygen and nitrogen species (RONS) can efficiently accelerate germination and growth in older seeds.

Coordination environment and fluoride binding of type 2 copper in the blue copper protein ascorbate oxidase

The coordination environment of the type 2 (nonblue) copper in native ascorbate oxidase (L-ascorbate:oxygen oxidoreductase, EC 1.10.3.3) and of a derivative of the enzyme having the type 1 (blue) copper reversibly bleached has been examined by electron paramagnetic resonance (EPR) spectroscopy. In the g[unk] region of the spectrum of bleached ascorbate oxidase, a seven-line superhyperfine pattern is seen that is attributed to the presence of three nitrogen-donor ligands to a type 2 copper having tetragonal geometry. The superhyperfine splitting patterns in the g parallel region of the EPR spectra of native and bleached ascorbate oxidase show that as many as two fluorides may bind to type 2 copper. Because fluoride inhibits the enzyme competitively with respect to ascorbic acid, it is proposed that the type 2 copper is part of the ascorbate binding site.

Proton magnetic relaxation dispersion in solutions of the cuproprotein diamine oxidase

Proton nuclear magnetic resonance relaxation measurements were made over the range 4.7--220 MHz for aqueous solutions of hog kidney diamine oxidase. The values of 1/T1 give rise in two distinct dispersions, at 16 and 75 MHz, whereas 1/T2 displays a minimum at 20 MHz. The temperature dependence of relaxation rates in all cases yield apparent activation energies less than 0.6 kcal/mol. These data indicate to us that the two Cu(II) ions of diamine oxidase are intrinsically different in terms of their electronic relaxation characteristics and hence, chemical environments. Low field limits of the two electronic relaxation times are 2 and 10 ns, with one of these correlation times being frequency dependent. The value of the frequency-dependent electronic relaxation time is governed by interactions that are modulated by a process having a correlation time of 5 ps.

Properties of nonheme iron in a cell envelope fraction from Escherichia coli

The reaction with o-phenanthroline of nonheme iron found in cell envelope fractions from Escherichia coli has been investigated. About 20% of the total nonheme iron reacts directly with o-phenanthroline. This iron appears to be in the ferric state but is reducible by protein sulfhydryl groups in the presence of the chelating agent. A further 20% of the nonheme iron will react with o-phenanthroline only in the presence of dithionite. Succinate can replace dithionite but only produces about 35% of the reaction given by dithionite. The reduction of cytochrome b(1) of the respiratory chain by succinate shows similar behavior to the reaction of iron with o-phenanthroline in the presence of succinate. Both of these components react completely only in the presence of 2-heptyl-4-hydroxyquinoline-N-oxide. The remaining 60% of the nonheme iron of the cell envelope will not react with o-phenanthroline even in the presence of dithionite or 6 m urea. Triton X-100 with dithionite will permit a small part (10%) of this iron to react with o-phenanthroline. The iron which does not react with o-phenanthroline is not associated with succinate, reduced nicotinamide adenine dinucleotide, or d-lactate dehydrogenases.

The function of ubiquinone in Escherichia coli

1. The function of ubiquinone in Escherichia coli was studied by using whole cells and membrane preparations of normal E. coli and of a mutant lacking ubiquinone. 2. The mutant lacking ubiquinone, strain AN59 (Ubi(-)), when grown under aerobic conditions, gave an anaerobic type of growth yield and produced large quantities of lactic acid, indicating that ubiquinone plays a vital role in electron transport. 3. NADH and lactate oxidase activities in membranes from strain AN59 (Ubi(-)) were greatly impaired and activity was restored by the addition of ubiquinone (Q-1). 4. Comparison of the percentage reduction of flavin, cytochrome b(1) and cytochrome a(2) in the aerobic steady state in membranes from the normal strain (AN62) and strain AN59 (Ubi(-)) and the effect of respiratory inhibitors on these percentages in membranes from strain AN62 suggest that ubiquinone functions at more than one site in the electron-transport chain. 5. Membranes from strain AN62, in the absence of substrate, showed an electron-spin-resonance signal attributed to ubisemiquinone. The amount of reduced ubiquinone (50%) found after rapid solvent extraction is consistent with the existence of ubiquinone in membranes as a stabilized ubisemiquinone. 6. The effects of piericidin A on membranes from strain AN62 suggest that this inhibitor acts at the ubiquinone sites: thus inhibition of electron transport is reversed by ubiquinone (Q-1); the aerobic steady-state oxidation-reduction levels of flavins and cytochrome b(1) in the presence of the inhibitor are raised to values approximating those found in the membranes of strain AN59 (Ubi(-)); the inhibitor rapidly eliminates the electron-spin-resonance signal attributed to ubisemiquinone and allows slow oxidation of endogenous ubiquinol in the absence of substrate and prevents reduction of ubiquinone in the presence of substrate. It is concluded that piericidin A separates ubiquinone from the remainder of the electron-transport chain. 7. A scheme is proposed in which ubisemiquinone, complexed to an electron carrier, functions in at least two positions in the electron-transport sequence.

"Rapidly appearing" molybdenum electron-paramagnetic-resonance signals from reduced xanthine oxidase

Further electron-paramagnetic-resonance studies relating to the role of molybdenum in the enzymic mechanisms of xanthine oxidase were carried out. The classification of the various molybdenum signals obtained on reducing the enzyme is briefly discussed. The group of ;Rapidly appearing' signals, which are obtained with all substrates within the turnover time and which show interaction with exchangeable protons, were studied in detail. Signals with salicylaldehyde, purine and xanthine in H(2)O and in 95% D(2)O were examined at 9 and 35GHz and interpreted with the help of computer simulation. Molybdenum atoms in a number of different chemical environments are involved, each substrate giving rise to two superimposed spectra with slightly different parameters; g values and proton splittings were determined. The spectrum with salicylaldehyde is believed to represent the reduced enzyme alone not in the form of a complex with substrate and its two constituents are believed to represent the two molybdenum atoms bonded slightly differently within the enzyme molecule. With purine and xanthine the spectra are thought to represent complexes of reduced enzyme with substrate molecules. With xanthine one signal-giving species shows coupling to two equivalent protons, whereas in all the other species observed two non-equivalent protons are involved. The origin of the protons is discussed in the light of the direct hydrogen-transfer mechanism implicated earlier for the enzyme. It is concluded that the proton derived from the substrate is located at least 3å from the molybdenum atom with which it interacts.

The number of iron atoms in the paramagnetic center (G =1.94) of reduced putidaredoxin, a nonheme iron protein

Images