Recent Deaths

Frederick, S. E.; Newcomb, E. H.

doi:10.1126/science.164.3879.537-b

Cited by 12 publications

(15 citation statements)

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“…It appears, therefore, that both in light-grown cotyledons and in etiolated cotyledons exposed to light, the preferential association of microbodies with plastids is related to increased glycolate oxidase activity, which in turn is presumably dependent upon the production of glycolate by photosynthesizing chloroplasts (50). Hence the close spatial relationship between the two organelles seen here under these conditions lends support to the conjecture of Frederick and Newcomb (15) that there is an interaction between the two organelles that probably reflects their mutual involvement in glycolate metabolism.…”

Section: Discussionsupporting

confidence: 69%

“…Glyoxysomes contain not only enzymes directly involved in 40), have been observed with the electron microscope in both leaves (15) and castor bean endosperm (55). These observations, coupled with cytochemical detection of catalase in the microbodies of castor bean endosperm (55,56) and leaves (16,17), indicate that microbodies are the morphological equivalents of glyoxysomes and peroxisomes and that the latter two biochemically defined particles have certain distinctive similarities.…”

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confidence: 61%

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Microbodies (Glyoxysomes and Peroxisomes) in Cucumber Cotyledons

et al. 1971

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Section: Discussionsupporting

confidence: 69%

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confidence: 61%

Microbodies (Glyoxysomes and Peroxisomes) in Cucumber Cotyledons

et al. 1971

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“…C02 production occurring in light is similar to photorespiration in higher plants (6). Phase contrast and electron microscopic examination showed that the preparation does not contain peroxisomes and only a small contamination of cytoplasm and mitochondria (8,19). Mitochondrial metabolism could not be detected (17).…”

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confidence: 75%

Intermediates Of Photosynthesis in Acetabularia mediterranie Chloroplasts

1970

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The chloroplast fraction isolated from Acetabularia mediterranie was exposed to 14CO2 as NaH'4C03 in light and darkness, and soluble radioactive compounds were analyzed at frequent intervals. The behavior of Calvin cycle intermediates on the chloroplasts isolated from 2 to 3 g of cells, about 2 cm long, each preparation containing 600 to 750 j,g of total chorophyll (1). The chloroplasts were suspended in 5 ml of the A medium described earlier (6), except that the pH was reduced to 7.2 in order to reduce the equilibrium bicarbonate concentration of the medium (15). As a result, the bicarbonate concentration was low enough that it probably became rate-limiting after about 10 min of photosynthesis (6), but it ensured maximum specific activity of fixed 4CO2 .Experimental. Chloroplast preparations were illuminated by fluorescent lights (2500 ft-c), and 100 ,uc of NaH14CO3 (specific radioactivity about 40 mc/mmole) were added. Sampling began immediately. Samples of 25 Al were withdrawn with a Schwartz Biopette automatic pipette and were quickly applied to the corner of 8-inch X 11-inch chromatography sheets (Whatman 3MM). These were immediately placed in liquid nitrogen until the end of the experiment (30-60 min). A few chromatograms were made with 50 or 100 ,ul. These did not have any spots which could not be seen on the 25 Al chromatograms, showing that all major compounds were being detected. With this technique, samples could be taken at intervals as short as 8 sec, although the sample size was apt to be erratic because of pipetting errors at this speed. Much of this problem was later eliminated by cutting the tips of the polyethylene pipettes at a sharp angle. Samples taken at longer intervals were in close agreement. The time from withdrawal of the sample to the freezing of the chromatograms was about 4 sec. In the dark fixation experiment (Table I), all conditions and procedures were identical except that the experiment was run in darkness.Chromatography and Radioautography. At the conclusion of the experiment chromatograms were removed singly from the liquid nitrogen, and the origins were fixed by 1-to 2-min exposure to the hot vapors of vigorously boiling ethanol. This procedure avoids the problems of extraction and concentration and reduces the nonbiological breakdown of labile intermediates to a minimum (5). Two-dimensional chromatograms were run in 80% phenol at pH 5.4 and butanol-acetic acid-water (12:3:5) and radioautographed. Representative radioautographs are shown in Figure 1. The spots were cut out and counted on both sides in an ultrathin window gas flow Geiger-Mueller counter. The counts from both sides were averaged (4) and corrected for coincidence. All results are presented as counts per minute per sample as determined from a 25 MAl chromatogram, and they are strictly comparable within each experiment. The sum of radioactivities of all the compounds that moved from the origin was called "soluble radioactivity," and the radioactivity which did not move from the origin was termed "insolu...

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“…Although it is likely that these transients are isolated from the oxygen production site through the membrane organization system, it still remains important to maintain chloroplast 02 concentration low. The tight spatial appression of glyoxysome and chloroplast membranes observed in electron micrographs (13) suggests that the glycolate oxidase reaction's fundamental function may be depletion of molecular oxygen produced by the photosynthetic apparatus.…”

Section: Resultsmentioning

confidence: 99%

Photosynthesis and Photorespiration in Typha latifolia

McNaughton

Fullem

1970

Plant Physiol.

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NaH'4CO3 (105 Cpm) to 1.3 ml of the enzyme preparation. At intervals, 0.4-ml samples were removed and acidified with 0.1 ml of 6 N acetic acid. Controls consisted of a zero time sample that was acidified immediately upon mixing the reaction components, and a reaction mixture lacking ribulose-1, 5-diP which was acidified at the end of the experimental period. The same enzyme preparation procedure was used for phosphopyruvate carboxylase except that dithioerythritol was sometimes substituted for reduced glutathione to provide an alternative test for sulfhydryl protection. The assay system for this enzyme, after Slack and Hatch (25), contained 1.55 ,umoles of phosphopyruvate and 15 ,umoles of sodium glutamate in substitution for the ribulose-1,5-diP used above. Controls were the same. For the assay of glycolate oxidase activity, leaves were homogenized in 0.067 M phosphate buffer (pH 7.8) and filtered through four layers of 60 mesh cheesecloth. This homogenate was used directly in a polarographic assay (10) with the Clark electrode. The reaction was initiated by adding 10 .moles of sodium glycolate in 0.2 ml of the phosphate buffer to 2.8 ml of the enzyme preparation. Controls were samples to which no glycolate was added. Addition of the enzyme cofactor, flavin mononucleotide, was not found to be stimulatory, and this was omitted from the assay system. Reagents were from Sigma.For "4CO0 assimilation experiments, leaves were preilluminated in 2 X 106 ergs cm-2 sec-l of light with their base in distilled water or a glycolate oxidase inhibitor, 0.01 M a-hydroxypyridinemethanesulfonic acid (Aldrich), for 30 min prior to release of "4CO2 by the acidification of a bicarbonate solution. Carbon dioxide concentration was 370 ,ul liter-' after addition of bicarbonate, to eliminate artifacts arising from high CO2 concentrations. Following 10 min of photosynthesis with water or 20 min with the inhibitor, the leaves were killed with boiling 80%-ethanol. In the controls, 1.8 AC of "CO, were used. In the experiments with inhibitor, 2.02 ,C of "CO2 were used. The different time periods and specific radioactivities of "CO2 were used to assure that approximately the same amount of radioactivity would be recovered from chromatograms of both treatments without overloading with plant extracts. Total cpm recovered from chromatograms per g of leaf extracted were 43,200 + 21,600 (0.95 confidence interval) for the water controls and 53,600 + 8,300 for experiments in inhibitor. For

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Recent Deaths

Cited by 12 publications

References 0 publications

Microbodies (Glyoxysomes and Peroxisomes) in Cucumber Cotyledons

Microbodies (Glyoxysomes and Peroxisomes) in Cucumber Cotyledons

Intermediates Of Photosynthesis in Acetabularia mediterranie Chloroplasts

Photosynthesis and Photorespiration in Typha latifolia

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