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Biomedical subjects

Y M Heimer

Publications and source records attributed to Y M Heimer.

At least 19 recordsLinked to original sources
PubMed2002

Mitochondrial involvement in tracheary element programmed cell death.

The mitochondria pathway is regarded as a central component of some types of programmed cell death (PCD) in animal cells where specific signals cause the release of cytochrome c from mitochondria to trigger a proteolytic cascade involving caspases. However, plant cells lack canonical caspases, therefore a role for the mitochondria in programmed cell death in plant cells is not obvious. Using plant cells which terminally differentiate, we provide evidence supporting the involvement of mitochondria in PCD, however the release of cytochrome c is insufficient to trigger the PCD. Prior to execution of cellular autolysis initiated by the rupture of the large central vacuole to release sequestered hydrolases, mitochondria adopt a definable morphology, the inner membrane depolarizes prior to death, and cytochrome c is released from mitochondria. However, PCD can be blocked despite translocation of cytochrome c. These results suggest a role for the mitochondria in this PCD but do not support the current animal model for a causative role of cytochrome c in triggering PCD.

Apoptosis↗
PubMed2000

Triacylglycerols of the red microalga Porphyridium cruentum can contribute to the biosynthesis of eukaryotic galactolipids.

A mutant of the red microalga Porphyridium cruentum was selected on the basis of impaired growth at suboptimal temperatures (15 vs. 25 degrees C). Fatty acid and lipid analyses revealed diminished proportions of eicosapentaenoic acid (from 41 to 30%) and of the eukaryotic molecular species (from 38 to 28% of monogalactosyldiacylglycerol (MGDG) and elevated proportion (10 vs. 2%) of triacylglycerols (TAG) in the mutant, as compared with the wild type. Pulse labeling of the wild type cells with radioactive fatty acid precursors indicated an initial incorporation of the fatty acids into phosphatidylcholine (PC) and TAG. Following the pulse, the label of PC and TAG decreased with time (from 25 to 5% of the total dpm in TAG) while that of chloroplastic polar lipids, mainly MGDG, continued to increase. In the mutant, however, the labeling of TAG after the pulse was higher (30% of the total dpm) than that of the wild type and decreased only slightly to 20%. This may indicate that in P. cruentum, TAG can contribute to the biosynthesis of eukaryotic species of MGDG.

Chlorophyll↗
PubMed1997

Fatty acid unsaturation in the red alga Porphyridium cruentum. Is the methylene interrupted nature of polyunsaturated fatty acids an intrinsic property of the desaturases?

Polyunsaturated fatty acids (PUFAs) exogenously supplied to the red microalga Porphyridium cruentum were incorporated into cellular lipids. All the C18 PUFAs studied were desaturated by a delta 6-desaturase and all the C20 PUFAs by a delta 5-desaturase. The latter enzyme desaturated even 20:2(11, 14) to 20:3(5, 11, 14) and 20:3(11, 14, 17) to 20:4(5, 11, 14, 17). We infer the existence of several fatty acid desaturases, with different chain length specificities. Furthermore, the introduction of double bonds in a methylene interrupted pattern, at least for alpha-type desaturase such as the delta 5- and delta 6-desaturases, is not an intrinsic property of the enzyme but a consequence of the arrangement of the pre-existing double bonds in the fatty acid substrate.

Eukaryota↗
PubMed1996

Biosynthesis of eicosapentaenoic acid in the microalga Porphyridium cruentum. I: The use of externally supplied fatty acids.

The biosynthetic pathways of eicosapentaenoic acid (20:5n-3) in microalgae, in general, and in Porphyridium cruentum, in particular, are not known. Some of the putative intermediates along the suggested pathways could not be detected probably due to their low endogenous level. In order to increase the endogenous levels of the intermediates, we provided various fatty acids in the growth medium. Exogenously supplied fatty acids were indeed incorporated into algal lipids and were further metabolized along the n-6 and n-3 pathways. In the n-6 pathway, 18:2 was desaturated to 18:3n-6, elongated to 20:3n-6, and subsequently desaturated to 20:4n-6 and then to 20:5n-3. In the n-3 pathway, 18:2 was first desaturated to 18:3n-3 which was then sequentially converted, apparently by the same enzymatic sequence of the n-6 pathway to 18:4n-3, 20:4n-3, and 20:5n-3.

Eicosapentaenoic Acid↗
PubMed1995

A chimeric Lhcb::Nia gene: an inducible counter selection system for mutants in the phytochrome signal transduction pathway.

One approach towards understanding the transduction pathways of phytochromes is the selection of mutants impaired in various steps. We report here the construction of an inducible counter-selection system for such mutants employing the enzyme nitrate reductase. This enzyme can convert the benign substrate analogue chlorate to the toxic product chlorite, resulting in severe growth inhibition. An Arabidopsis thaliana nitrate reductase gene (Nial*2) was placed under the regulation of an Arabidopsis thaliana light-harvesting chlorophyll a/b protein (Lhcb1*3) promoter that is phytochrome-responsive. The chimeric Lhcb::Nia gene was transformed into A. thaliana. Homozygous transformant lines were selected and grown in the absence of nitrate and the presence of L-glutamine, conditions that substantially inhibited the expression of the endogenous nitrate reductase genes. In darkness seedlings of the transformed lines were resistant to chlorate; however, when seedlings were grown with intermittent red light, increased sensitivity to chlorate was observed. This sensitivity was correlated with an increase in both Nia1*2 RNA levels and nitrate reductase activity. The resistant seedlings were clearly distinguishable from the sensitive ones based on hypocotyl length, with no overlap in this parameter between the two populations. Thus, this system should allow for the selection of mutants that are impaired in phytochrome regulation of the transcription of Lhcb genes.

Arabidopsis↗
PubMed1992

Overproduction of gamma-Linolenic and Eicosapentaenoic Acids by Algae.

The pharmaceutical interest and limited availability of gamma-linolenic acid (GLA) and eicosapentaenoic acid (EPA) prompted the search for genetic means for increasing the production of these fatty acids from algal sources. Cell lines of Spirulina platensis and Porphyridium cruentum resistant to the growth inhibition of the herbicide Sandoz 9785 were selected by serial transfers of the culture in the presence of increasing concentrations of the herbicide. The resistant cell lines of S. platensis overproduced GLA and those of P. cruentum overproduced EPA and were stable for at least 50 generations in the absence of the inhibitor.

Journal Article↗
PubMed1990

Delta6 desaturase inhibition : a novel mode of action of norflurazone.

The herbicide Norflurazone was shown to be an inhibitor of fatty acid of the Delta6 desaturation system. Treating cultures of the microalgae Spirulina platensis or Monodus subterraneus with this herbicide brought about a reduction in the level of gamma-linolenic acid and in an increase in the level of linoleic acid. In Monodus, the increase in linoleic acid made it more available for omega3 desaturation, resulting in an increase in the proportion of eicosapentaenoic acid. The proportion of arachidonic acid did not decrease albeit the drastic decrease in its precursor gamma-linolenic acid.

Journal Article↗
PubMed1983

Differential inhibition of cellular RNAs by photosensitized trioxalen.

Treatment of mouse cell cultures with 5 X 10(-6)M trioxalen (4,5',8-trimethylpsoralen, or TMP) followed by long wavelength ("near") UV-irradiation (NUV) resulted in immediate cessation of most of the cellular transcriptional activity. The effective inhibitory TMP concentrations for ribosomal RNA were lower than those affecting poly RNA containing RNA. Low molecular RNA species were only partially inhibited. Side effects, commonly caused by other drugs, were not detected. These properties, and the simplicity of their use, make psoralens attractive inhibitors of RNA biosynthesis.

Animals↗
PubMed1983

Psoralen plus near-ultraviolet light: a possible new method for measuring DNA repair synthesis.

A new method is proposed to inhibit semiconservative DNA synthesis in cultured cells while DNA repair synthesis is being measured. The cells are treated with the DNA-crosslinking agent Trioxalen (4,5,8-trimethylpsoralen) plus near-ultraviolet light, and consequently 99.5% inhibition of replicative DNA synthesis is achieved. Additional DNA-damaging agents induce thymidine incorporation into the double-stranded regions of the DNA. The new method gave results very similar to those obtained with the benzoylated naphthoylated DEAE (BND) cellulose method using three human fibroblast strains, of which one had deficient capacity for DNA repair synthesis following treatment with gamma rays and methyl methanesulfonate. The advantages of the new method are simplicity and rapidity, as well as the high extent to which replicative DNA synthesis is inhibited.

Cell Line↗
PubMed1982

Characterization of ornithine decarboxylase of tobacco cells and tomato ovaries.

Some characteristics of L-ornithine decarboxylase of tomato ovaries and tobacco cells are described. The enzyme has a pH optimum of 8.0. It requires pyridoxal phosphate and thiol reagent (dithiothreitol) for activity. It is specific for L-ornithine and has an apparent Km of 1.4 X 10-4 M. It has an apparent molecular weight of 107000. Putrescine inhibited the activity in vitro. Spermidine and spermine also inhibit the enzyme, but less effectively. It is concluded that the enzyme is similar to that of mammalian origin and likewise fulfils a function related to cell proliferation.

Amino Acids↗
PubMed1982

Fractionated low-level gamma irradiation of Chinese Hamster cells: cellular and biochemical effects.

Chinese hamster V79 cells in log-phase were exposed daily to 0.6 Gy of gamma radiation for 3-6 months. After such an exposure the population doubling time increased from 10 to 15 h. When irradiation was discontinued doubling time gradually decreased. Cell survival following acute radiation dose of the low-level irradiated cells remained the same as that of untreated cells. The fractionated irradiation did not affect the capacity of the cells to perform DNA repair synthesis. Likewise, the sensitivity to inhibition by acute radiation exposure of the ability to induce ornithine decarboxylase activity was similar in cells exposed to fractionated irradiation and in untreated cells. It is concluded that there is no apparent effect of sublethal radiation dose received in one generation on the radiation sensitivity of the succeeding generations during the log-phase of growth.

Animals↗
PubMed1982

Participation of ornithine decarboxylase in early stages of tomato fruit development.

The apparent association of ornithine decarboxylase (ODC) with rapid cell proliferation in developing tomato (Lycopersicon esculentum Mill. cv. Pearson ms-35) fruits has been previously described. Further evidence is provided by the use of two ODC inhibitors, alpha-difluoromethylornithine (alpha-DFMO) and alpha-methylornithine (alpha-MO). Fruit development was inhibited by these inhibitors if applied during the period of intensive cell division. When applied in vitro, the two inhibitors were shown to inhibit the activity of ODC but not that of arginine decarboxylase (ADC). When applied in vivo, alpha-DFMO, a catalytic irreversible inhibitor, caused 97.1% reduction of ODC activity in the dialyzed extract from the treated ovaries, while it had no effect on ADC. On the other hand, alpha-MO, a reversible inhibitor, did not reduce the activity of these two enzymes in the dialyzed extracts when applied in vivo. The dialysis procedure probably removed alpha-MO from the enzyme fraction. Putrescine, the product of both ODC and ADC, alleviated the inhibition of fruit development but did not restore ODC activity to the control level. These results suggest that in the young developing tomato fruit, ODC is the enzyme responsible for the synthesis of putrescine, which is essential for the early stages of fruit development. The reduced activity of ODC elicited by putrescine suggests a mechanism of feedback regulation by enzyme repression or release of an ODC anti-enzyme.

Journal Article↗
PubMed1982

Ornithine decarboxylase and arginine decarboxylase activities in meristematic tissues of tomato and potato plants.

Ornithine decarboxylase and arginine decarboxylase activities were measured in roots and buds of tomato (Lycopersicon esculentum Mill. cv. Pearson ms-35) and potato (Solanum tuberosum cv. Desire) plants. In both tomato and potato, the activity of ornithine decarboxylase was the highest at the root tip, decreasing proximally. The same was true for potato buds. In vegetative buds of tomato, the highest activity was found in the youngest leaves. The older the leaf, the lower was orithine decarboxylase activity. Arginine decarboxylase, on the other hand, did not display a similar gradient. These findings are in accordance with the suggestion that in tomato and potato elevated ornithine decarboxylase activity is associated with intense mitotic activity.

Journal Article↗
PubMed1981

An apparent correlation between the inhibition of induced ornithine decarboxylase activity by gamma radiation and the capacity for DNA repair synthesis in normal and ataxia telangiectasia human fibroblasts: no correlation with cell survival.

Exposure of normal human fibroblasts (F107) in stationary phase to gamma radiation inhibited the appearance of induced ornithine decarboxylase (ODC) activity. Skin fibroblasts derived from two ataxia telangiectasia (AT) patients (F184 and F182) displayed a similar response. The level of DNA repair synthesis was also similar in the three cell strains. Fibroblasts from another apparently normal donor (F196) were very sensitive to inhibition of induced ODC activity by gamma radiation and were also deficient in radiation-induced DNA repair synthesis. However, the two strains derived from normal donors displayed the same degree of cellular sensitivity towards X-rays, whereas the two AT strains showed the typical hypersensitivity to the cytotoxic effect of X-irradiation. The results suggest a possible correlation between the inhibition of induced ODC activity by gamma radiation and the extent of DNA repair synthesis at high radiation doses, but there is no correlation between these two parameters and cellular survival at low radiation doses.

Ataxia Telangiectasia↗
PubMed1981

Gamma radiation inhibits the appearance of induced ornithine decarboxylase activity in Chinese hamster cells.

Ornithine decarboxylase activity of Chinese hamster cells (ODC, EC 4.1.1.17) can be induced in plateau phase by change of medium. Exposure of the cells to gamma radiation before induction reduces the amount of ODC activity induced. The dose-response curve is exponential with a D0 of 106 krad. Exposure of BUdR-substituted cells is more effective in reducing ODC induction at high doses, with a D0 of 38 krad. Cells can recover from the reduction incurred by 74 krad if enzyme induction is delayed for 2 hours after exposure. Treatment of the cells with psoralen-plus-light completely inhibits RNA synthesis without affecting protein synthesis (Heimer, Ben-Hur and Riklis 1977, 1978). Using this procedure it is shown that the effect of gamma radiation on inducible ODC activity is due not only to DNA damage by also involves a post-transcriptional effect. This conclusion is supported by employing a heat shock to inhibit protein synthesis prior to gamma-irradiation of log-phase cells. In such cells the increased activity of ODC upon transfer to 37 degrees C is due primarily to enzyme synthesis using pre-existing RNA species during the first few hours. A low concentration of actinomycin D, which inhibits rRNA synthesis, applied during the recovery period, prevents the recovery of the cells' capacity for maximal ODC induction. This may indicate that, in order to recover, the cells have to repair damage to the ribosomes as well as to DNA.

Animals↗
PubMed1979

Inhibition by trioxalen (psoralen) plus near-ultraviolet light of the induction of ornithine decarboxylase in Chinese-hamster cells.

Trioxalen (trimethylpsoralen) plus near-u.v. light, a potent inhibitor of DNA and RNA synthesis, inhibits the induction of ornithine decarboxylase in stationary-phase V79 fibroblasts. It does not affect the translation of pre-existing mRNA. The method, in view of its high degree of specificity and precise timing, is a better choice for inhibiting RNA synthesis than the commonly used chemical inhibitors and precursor analogues.

Animals↗