Formation of Hydrogen Peroxide by NAD(P)H Oxidation with Isolated Cell Wall-Associated Peroxidase from Cultured Liverwort Cells, Marchantia polymorpha L.

Hydrogen peroxide was formed in isolated cell walls from Marchantiapolymorpha L. in the presence of MnCl₂ by either NADH or NADPHoxidation. This reaction was stimulated by phenols such as 2,4-dichlorophenolor p-coumarate, suggesting a reaction similar to that proposedfor the last step of lignification in higher plant cells, althoughbryophytes have been reported to be devoid of lignin. (Received June 16, 1987; Accepted March 3, 1987)     

Oxidation and reduction of cytochrome c bound to the phosphoprotein phosvitin

The oxidation-reduction reactions and structural characteristics of phosvitin-bound cytochrome c were examined at various ratios of cytochrome c to phosvitin. At binding ratios below half the maximum, the rate constants for the oxidation reactions with cytochrome c oxidase and ferricyanide and the rate constants for the reduction reactions with cytochrome b2 and ascorbate were low, but at higher ratios these rate constants gradually increased to that of free cytochrome c and, in particular, the rate constant for oxidation by cytochrome c oxidase was raised to two to three times that of the free form. This binding-ratio dependence of the rate constants for the oxidation and reduction reactions was different from that of the net charge of the cytochrome c-phosvitin complex, implying that the negative charges of phosvitin are unlikely to modulate the rates. In contrast, the broadening of the NMR signals for the heme and methionine-80 methyl groups and the conformational transition in the vicinity of the heme moiety on change from the native to the cyanide-bound or urea-denatured form of cytochrome c showed a similar binding-ratio dependence to the rate constants for the oxidation and reduction reactions. Since the conformation and electronic structure in the heme environment of ferric and ferrous cytochromes c were not changed significantly by binding to phosvitin, and since the binding strength of cytochrome c to phosvitin at binding ratios below half the maximum is different from that at higher ratios, these findings suggest that a difference in the movement of cytochrome c in its complex with phosvitin may modulate its oxidation-reduction reactions.     

Effect of dinitrophenyl modification on oxidation-reduction of glutathione reductase from yeast

Covalent modification of glutathione reductase (GR) from yeast with 1-fluoro-2,4-dinitrobenzene (FDNB) inhibited the NADPH-GSSG reductase activity completely. This modification also decreased the NADPH-thio-NADP+ transhydrogenase activity, stimulated the NADPH-oxidase activity, and induced the NADPH-cytochrome c reductase activity. Spectrophotometric titration showed that one tyrosine residue per FAD was modified with a dinitrophenyl group. The modified enzyme showed conversion of the two-electron reduced form (EH2) to the four-electron reduced form (EH4) in anaerobic conditions and conversion of EH2 to the oxidized form (E) in aerobic conditions. These results indicate that the modification of one tyrosine residue of the active site induces the instability of EH2.     

Aspartate aminotransferase isozymes from rabbit liver. Purification and properties

Cytosolic and mitochondrial isozymes of aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase [EC 2.6.1.1] ) were purified to homogeneity from rabbit liver. The rabbit liver isozymes were closely similar to the corresponding isozymes from other sources, including human heart, pig heart, chicken heart, and rat liver, in their molecular weights, absorption spectra, amino acid compositions, isoelectric points, and Michaelis constants for the substrates. The NH2-terminal amino acid sequences of rabbit liver isozymes were identified up to 30 residues, and showed some differences from those of the corresponding isozymes obtained from other animals so far studied.     

Application of radiotelemetry to the survey of acorn dispersal byApodemus mice

We examined the applicability of radiotelemetry to studies of acorn dispersal byApodemus mice and compared its efficiency with the of this spool-and-line method. Installation of a transmitter (2.2 g) onto acorns did not interfere with the transporting and feeding behavior of the mice. We were able to detect all transmitter-installed acorns and follow the daily changes in the sites in which they were hoarded, while we missed 59% of the spool-tied acorns due to mice breaking the threads. Mice carried transmitter-installed acorns farther than spool-tied ones. The radiotelemetry method is superior to the spool-and-line method and useful for the study of hoarding behavior in rodents.     

Enantioselective pharmacokinetics of homochlorcyclizine: III. Simultaneous determination of (+)- and (−)- homochlorcyclizine in human urine by high-performance liquid chromatography

A method is described for the simultaneous determination of (+)- and (−)-homochlorcyclizine (HCZ) in human urine by high-performance liquid chromatography on a chiral stationary phase of ovomucoid-bonded silica. The pH of the buffer and organic modifier in the mobile phase markedly affected the chromatographic separation. A mobile phase of methanol—0.02 M acetate buffer (pH 4.7) (25:75, v/v) at a flow-rate of 1.0 ml/min was used for the urine assays. The ultraviolet absorption was monitored at 240 nm, and diphenhydramine was employed as the internal standard for the quantitation. (+)-HCZ, (−)-HCZ and the internal standard were eluted at retention times of 15, 25 and 8 min, respectively. The limit of determination for HCZ enantiomers was ca. 50 ng/ml of urine. One of the metabolites in human urine, which was a quaternary ammonium-linked glucuronide, could also be determined in a manner similar to unchanged HCZ after β-glucuronidase hydrolysis. A pharmacokinetic study was conducted with three healthy volunteers, who each received a single oral dose of racemic HCZ (20 mg). Distinct differences were found between the two enantiomers, particularly in the metabolic process, that is, the urinary excretion as (−)-HCZ-glucuronide within 48 h was ca. four times higher than that of the (+)-isomer. This method should be very useful for enantioselective pharmacokinetic studies of HCZ.     

Intramolecular disulfide linked alphabeta and alphaalpha in oxidized tropomyosin: separation, identification, and process of formation

The oxidation of rabbit skeletal tropomyosin (TM) by repeated cycles of freezing and melting in 0.3 mM Na bicarbonate was studied by electrophoresis and column chromatography. The oxidized TM showed two bands at ca. 70,000 daltons on sodium dodecyl sulfate (SDS)-polyacrylamide gels. Each band component was separated into disulfide-linked alphabeta and alphaalpha by carboxymethyl cellulose (CMC) column chromatography in urea. Oxidized TM before fractionation, as well as the alphabeta and alphaalpha components, was found to have a molecular weight of about 80,000 daltons, indicating the disulfide bonds to be primarily intramolecular. Oxidation of dilute TM in 1 M NaCl by exposure to air also produced disulfide-linked alphabeta. Partially oxidized TM was found to separate into beta, alphabeta, alpha, and alphaalpha on CMC chromatography, and these were eluted with a linear gradient of NaCl at molarities of ca. 0.09, 0.11, 0.12, and 0.14 M, respectively. The oxidation process was investigated by CMC chromatography, and a possible mechanism is presented. The alphabeta and alphaalpha components may exist as dominant component in TM in vitro rather than as a random mixture of two subunits. A splitting of the electrophoretic band of the alpha subunit into a doublet was observed.     

Relation of the structure and function of ferricytochrome c bound to the phosphoprotein phosvitin

The relationship between the structure and function of ferricytochrome c bound to the phosphoprotein phosvitin was investigated. The rates of reduction of phosvitin-bound ferricytochrome c by cytochrome b2, ascorbate and the superoxide radical generated by xanthine oxidase wer repressed where the binding ratio was less than half the maximum, but at higher ratios they were restored gradually with increase in the ratio. The affinity of cytochrome b2 for cytochrome c was not affected by binding of cytochrome c to phosvitin. The redox potential of the bond form was lower than that of the free form and only decreased with decrease in the ratio. The conformatin around the heme moiety and the electronic structure of the heme group of bound ferricytochrome c were similar to those of free ferricytochrome c, but the conformational stability in the vicinity of the prosthetic group was related to the binding ratio as ratios above half the maximum and was well correlated with the reduction rate. Since the binding of cytochrome c to phosvitin is much stronger at binding ratios below half the maximum, these results suggest that this binding strength exclusively affects the conformational flexibility of the heme crevice in the cytochrome molecule, thus altering the reduction rate.     

Mechanisms of generation of oxygen radicals and reductive mobilization of ferritin iron by lipoamide dehydrogenase.

The oxidase reaction of lipoamide dehydrogenase with NADH generates superoxide radicals and hydrogen peroxide under aerobic conditions. ESR spin trapping using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was applied to characterize the oxygen radical species generated by lipoamide dehydrogenase and the mechanism of their generation. During the oxidase reaction of lipoamide dehydrogenase, DMPO-OOH and DMPO-OH signals were observed. The DMPO-OOH signal disappeared on addition of superoxide dismutase. These results demonstrate that the DMPO-OOH adduct was produced from the superoxide radical generated by lipoamide dehydrogenase. In the presence of dimethyl sulfoxide, a DMPO-CH3 signal appeared at the expense of the DMPO-OH signal, indicating that the DMPO-OH adduct was produced directly from the hydroxyl radical rather than by decomposition of the DMPO-OOH adduct. The DMPO-OH signal decreased on addition of superoxide dismutase, catalase, or diethylenetriaminepentaacetic acid, indicating that the hydroxyl radical was generated via the metal-catalyzed Haber-Weiss reaction from the superoxide radical and hydrogen peroxide. Addition of ferritin to the NADH-lipoamide dehydrogenase system resulted in a decrease of the DMPO-OOH signal, indicating that the superoxide radical interacted with ferritin iron.