Biomedical subjects

Barbara S Berlett

Publications and source records attributed to Barbara S Berlett.

4 recordsLinked to original sources

PubMed2005

Protein oxidation by the cytochrome P450 mixed-function oxidation system.

This mini-review summarizes results of studies on the oxidation of proteins and low-density lipoprotein (LDL) by various mixed-function oxidation (MFO) systems. Oxidation of LDL by the O2/FeCl3/H2O2/ascorbate MFO system is dependent on all four components and is much greater when reactions are carried out in the presence of a physiological bicarbonate/CO2 buffer system as compared to phosphate buffer. However, FeCl3 in this system could be replaced by hemin or the heme-containing protein, hemoglobin, or cytochrome c. Oxidation of LDL by the O2/cytochrome P450 cytochrome c reductase/NADPH/FeCl3 MFO system is only slightly higher (25%) in the bicarbonate/CO2 buffer as compared to phosphate buffer, but is dependent on all components except FeCl3. Omission of FeCl3 led to a 60% loss of activity. These results suggest that peroxymonobicarbonate and/or free radical derivatives of bicarbonate ion and/or CO2 might contribute to LDL oxidation by these MFO systems.

Animals↗

PubMed2005

Effect of bicarbonate on iron-mediated oxidation of low-density lipoprotein.

Oxidation of low-density lipoprotein (LDL) may play an important role in atherosclerosis. We studied the effects of bicarbonate/CO2 and phosphate buffer systems on metal ion-catalyzed oxidation of LDL to malondialdehyde (MDA) and to protein carbonyl and MetO derivatives. Our results revealed that LDL oxidation in mixtures containing free iron or heme derivatives was much greater in bicarbonate/CO2 compared with phosphate buffer. However, when copper was substituted for iron in these mixtures, the rate of LDL oxidation in both buffers was similar. Iron-catalyzed oxidation of LDL was highly sensitive to inhibition by phosphate. Presence of 0.3-0.5 mM phosphate, characteristic of human serum, led to 30-40% inhibition of LDL oxidation in bicarbonate/CO2 buffer. Iron-catalyzed oxidation of LDL to MDA in phosphate buffer was inhibited by increasing concentrations of albumin (10-200 microM), whereas MDA formation in bicarbonate/CO2 buffer was stimulated by 10-50 microM albumin but inhibited by higher concentrations. However, albumin stimulated the oxidation of LDL proteins to carbonyl derivatives at all concentrations examined in both buffers. Conversion of LDL to MDA in bicarbonate/CO2 buffer was greatly stimulated by ADP, ATP, and EDTA but only when EDTA was added at a concentration equal to that of iron. At higher than stoichiometric concentrations, EDTA prevented oxidation of LDL. Results of these studies suggest that interactions between bicarbonate and iron or heme derivatives leads to complexes with redox potentials that favor the generation of reactive oxygen species and/or to the generation of highly reactive CO2 anion or bicarbonate radical that facilitates LDL oxidation.

Bicarbonates↗

PubMed2004

Investigations into the role of the plastidial peptide methionine sulfoxide reductase in response to oxidative stress in Arabidopsis.

Peptidyl Met residues are readily oxidized by reactive oxygen species to form Met sulfoxide. The enzyme peptide Met sulfoxide reductase (PMSR) catalyzes the reduction of Met sulfoxides back to Met. In doing so, PMSR is proposed to act as a last-chance antioxidant, repairing proteins damaged from oxidative stress. To assess the role of this enzyme in plants, we generated multiple transgenic lines with altered expression levels of the plastid form of PMSR (PMSR4). In transgenic plants, PMSR4 expression ranged from 95% to 40% (antisense) and more than 600% (overexpressing lines) of wild-type plants. Under optimal growing conditions, there is no effect of the transgene on the phenotype of the plants. When exposed to different oxidative stress conditions-methyl viologen, ozone, and high light-differences were observed in the rate of photosynthesis, the maximum quantum yield (Fv/Fm ratio), and the Met sulfoxide content of the isolated chloroplast. Plants that overexpressed PMSR4 were more resistant to oxidative damage localized in the chloroplast, and plants that underexpressed PMSR4 were more susceptible. The Met sulfoxide levels in proteins of the soluble fraction of chloroplasts were increased by methyl viologen and ozone, but not by high-light treatment. Under stress conditions, the overexpression of PMSR4 lowered the sulfoxide content and underexpression resulted in an overall increase in content.

Arabidopsis↗

PubMedDate not supplied

Cyclic oxidation and reduction of protein methionine residues is an important antioxidant mechanism.

Almost all forms of reactive oxygen species (ROS) oxidize methionine residues of proteins to a mixture of the R- and S-isomers of methionine sulfoxide. Because organisms contain methionine sulfoxide reductases (Msr's) that can catalyze the thioredoxin-dependent reduction of the sulfoxides back to methionine, it was proposed that the cyclic oxidation/reduction of methionine residues might serve as antioxidants to scavenge ROS, and also to facilitate the regulation of critical enzyme activities. We summarize here results of studies showing that organisms possess two different forms of Msr--namely, MsrA that catalyzes reduction of the S-isomer and MsrB that catalyzes the reduction of the R-isomer. Deletion of the msrA gene in mice leads to increased sensitivity to oxidative stress and to a decrease (40%) in the maximum lifespan. This suggests that elimination of both Msr's would have more serious consequences.

Animals↗