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Biomedical subjects

R Mittler

Publications and source records attributed to R Mittler.

25 records · Page 2Linked to original sources
PubMed1992

A unique ascorbate peroxidase active component in the cyanobacterium Synechococcus PCC 7942 (R2).

Ascorbate peroxidase active component (APAC) was purified and characterized in Synechococcus PCC 9742 (R2) cells. APAC was isolated from freshly harvested cells, by ion exchange chromatography on DEAE cellulose, ultrafiltration through a 3000 dalton cut off filter and high pressure liquid chromatography through a reversed phase C-18 column. APAC was found to be extremely stable to harsh treatments of boiling water for 30 min, acidification to pH 2.0 and proteolytic digestion. A close correlation between activity and iron content of APAC was observed throughout the purification steps. E.S.R. spectrum of APAC showed a resonance line at g = 4.3 in the oxidized from. Peroxide reduction by ascorbate decreased the E.S.R. signal, which reappeared upon reoxidation by H2O2. The affinities of APAC to H2O2 and ascorbate were high (0.38 mM and 0.2 mM, respectively). Amino acid composition analysis of APAC revealed the presence of glutamic acid:glycine:cysteine residues at 2:1:1 ratio.

Ascorbate Peroxidases↗
PubMed1991

Purification and characterization of pea cytosolic ascorbate peroxidase.

The cytosolic isoform of ascorbate peroxidase was purified to homogeneity from 14-day-old pea (Pisum sativum L.) shoots. The enzyme is a homodimer with molecular weight of 57,500, composed of two subunits with molecular weight of 29,500. Spectral analysis and inhibitor studies were consistent with the presence of a heme moiety. When compared with ascorbate peroxidase activity derived from ruptured intact chloroplasts, the purified enzyme was found to have a higher stability, a broader pH optimum for activity, and the capacity to utilize alternate electron donors. Unlike classical plant peroxidases, the cytosolic ascorbate peroxidase had a very high preference for ascorbate as an electron donor and was specifically inhibited by p-chloromercurisulfonic acid and hydroxyurea. Antibodies raised against the cytosolic ascorbate peroxidase from pea did not cross-react with either protein extracts obtained from intact pea chloroplasts or horseradish peroxidase. The amino acid sequence of the N-terminal region of the purified enzyme was determined. Little homology was observed among pea cytosolic ascorbate peroxidase, the tea chloroplastic ascorbate peroxidase, and horseradish peroxidase; homology was, however, found with chloroplastic ascorbate peroxidase isolated from spinach leaves.

Journal Article↗
PubMed1991

Antiperoxidative enzymes in Retama and their seasonal variation.

The antiperoxidative enzymatic activities of ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase and catalase and the content of the antioxidants ascorbate and glutathione were followed in the legume Retama (Retama reatem) in the desert. Antiperoxidative enzymatic activities and antioxidants content were related to seasonal variations in irradiance and precipitation. Retama was found to possess a very efficient removal mechanism for hydrogen peroxide as was shown by the high catalase activity and the high affinity of the ascorbate-glutathione pathway enzymes to their substrates. The increase in irradiance during the spring (March to May) was accompanied by increasing antioxidative enzymatic activities and ascorbate content. A marked enhancement in catalase activity also accompanied the increased light intensity during the spring. Changes in the enzymatic activities of the ascorbate-glutathione pathway followed the increased ascorbate content. These results suggest that physiological adaptation of Retama involves efficient H2O2 removal mechanisms which respond to different seasonal and environmental stresses.

Ascorbate Peroxidases↗
PubMed1991

Oxidative stress responses in the unicellular cyanobacterium Synechococcus PCC 7942.

Oxidative stress responses were tested in the unicellular cyanobacterium synechococcus PCC 7942 (R-2). Cells were exposed to hydrogen peroxide, cumene hydroperoxide and high light intensities. The extent and time course of oxidative stress were related to the activities of ascorbate peroxidase and catalase. Ascorbate peroxidase was found to be the major enzyme involved in the removal of hydrogen peroxide under the tested oxidative stress. Catalase activity was inhibited in cells, treated with high H2O2 concentrations, and was not induced under photooxidative stress. Catalase was specifically induced in cells treated with cumene hydroperoxide. Superoxide dismutase activity increased under conditions generating superoxide, such as high light intensities. The induction of the antioxidative enzymes was light dependent and was inhibited by chloramphenicol.

Ascorbate Peroxidases↗
PubMed1985

Activated human B cells display a functional IL 2 receptor.

These studies deal with the expression of a functional IL 2 receptor on activated primary human B cells. Antibody against the receptor (alpha-TAC) reacted with 25 to 65% activated B cells, inhibited B cell proliferation by 50% and inhibited B cell secretion of Ig by greater than 90%. These effects were shown to be independent of contaminating T lymphocytes. Anti-TAC immunoprecipitated a molecule of identical size (65,000 daltons) from T and B lymphocytes; B cells were also shown to actively synthesize the IL 2 receptor. The chymotryptic peptide chromatograms of TAC antigen from T and B cells show these molecules to be indistinguishable.

Antibodies, Monoclonal↗
PubMed1983

Antigenic modulation of pan-T-cell and T-cell subset-specific markers.

The time course and extent of antigenic modulation induced by monoclonal antibodies OKT3, OKT4, OKT8, BE2, and BE3 was investigated. OKT3-induced antigenic modulation could be detected as early as after 3-hr incubation with the antibody and almost total removal of the OKT3-reactive antigen was seen by 42 hr. This modulation did not decrease the expression of T-cell antigens detected by OKT4 and OKT8. OKT3-modulated cells reexpressed the antigen after 42-hr incubation in OKT3-free media. BE3 (homologue of OKT1) also caused modulation of its surface antigen after 24-hr incubation. In contrast, OKT4 did not induce modulation even after 42-hr incubation with high concentrations of OKT4 antibody. Approximately 43% of the OKT8-reactive lymphocytes could be induced to modulate this antigen. A tumor-associated antigen present on neoplastic lymphocytes from patients with cutaneous T-cell lymphoma, recognized by monoclonal antibody BE2, also was not induced to modulate. These results suggest that antigenic modulation and the fate of the modulated antibody may be of importance to immunotherapeutic applications of these reagents.

Animals↗