Effect of heme on Bacteroides distasonis catalase and aerotolerance

Parallel increases in intracellular catalase activity and resistance to extracellular H2O2 and to hyperbaric O2 toxicity were observed when Bacteroides distasonis VPI 4243 (ATCC 8503, type strain) was grown in either complex or defined medium containing graded amounts of hemin. Virtually all of the cells with high catalase activity (greater than 200 U/mg) remained viable upon exposure at 37 degrees C to 100-lb/in2 O2 on agar surfaces for 1 h, whereas low-catalase cells (less than 10 U/mg) lost 1.2 log units of viable cells during that treatment. Upon exposure to 500 microM H2O2, high-catalase cells lost 0.4 log units of the initial viable colonies during the same period in which low-catalase cells lost 3 log units of viable cells. The superoxide dismutase activity was the same in each test culture. These data support the role of intracellular catalase in protecting B. distasonis from oxidative damage resulting from hyperbaric oxygenation or H2O2 exposure. Catalase activity elicited by adding hemin to cells grown previously in medium lacking hemin was inhibited only 40% by prior incubation of the cells with chloramphenicol (30 micrograms/ml) and only 22% with rifampin (5 micrograms/ml). A model which is consistent with these data involves the production of an apocatalase in cells grown in low-hemin medium. Addition of hemin to the cells would result in a rapid chloramphenicolor rifampin-insensitive stimulation of catalase activity followed by further de novo biosynthesis of catalase.     

Isolation of intact polysomes from mechanically dehulled developing grain

A rapid method for obtaining large quantities of developing groats suitable for the isolation of highly intact polysomes has been developed. Developing spikelets were harvested directly from oat panicles into liquid nitrogen and then quickly passed through a dehuller. Chaff was removed by air aspiration and the resultant groats were collected directly back into liquid nitrogen. Approximately 250 g of groats could be isolated each man-hour by the above method. In comparison, only 10 g of endosperm could be collected by squeezing it out of spikelets using an endosperm mangle. Membrane-bound polysomes extracted from the immature groats were compared to those extracted from endosperm. The largest polysomes discernable as unique peaks on sucrose gradients were ten-mers and nine-mers for groats and endosperm, respectively. Polysomes isolated from both starting materials stimulated similar incorporations of [³⁵S]methionine into trichloroacetic acid-insoluble products during in vitro translations in wheat germ extract. Both polysome preparations directed the synthesis of similar high-molecular-weight proteins. Based on these criteria, polysomes from both preparations were found to be of similar intactness, although the groat starting material was much more readily obtained. The polysome classes having the maximum absorbance peak for endosperm and groat polysomes were six-mers and eight-mers, respectively.     

Some Properties of Thiosulfate-Oxidizing Enzyme from Marine Heterotroph 16B

Thiosulfate-oxidizing enzyme has been demonstrated in cell-free extracts of the marine, thiosulfate-oxidizing pseudomonad strain 16B. The enzyme, partially purified by ion-exchange chromatography and calcium phosphate gel treatment, catalyzed the oxidation of thiosulfate to tetrathionate with the concomitant reduction of ferricyanide. Native but not mammalian cytochrome c was also reduced by the enzyme in the presence of thiosulfate. The enzyme was located exclusively in the supernatant of ultracentrifuged cell extracts. The most purified enzyme preparation, like intact cells, exhibited a temperature optimum of 30 to 31°C. However, it exhibited no definite pH optimum. At pH 6.1 to 6.3 and 30°C, the K_m for thiosulfate was 1.57 mM. At lower temperatures, the apparent K_m for thiosulfate increased, but the apparent maximum velocity remained virtually unchanged. Thiosulfate oxidation in intact cells exhibited an increase in the pH optimum at lower temperatures. The thiosulfate-oxidizing enzyme of marine heterotroph 16B is compared with thiosulfate-oxidizing enzymes from other bacteria, and the effect of temperature on the relationship between pH and thiosulfate oxidation is discussed with reference to the natural habitat of the bacterium.     

Effect of dietary fiber on absorption of B-6 vitamers in a rat jejunal perfusion study

Previous research has indicated that dietary fiber may affect the absorption and utilization of certain nutrients. To determine the effect of certain fiber materials on the absorption of B-6 vitamers, jejunal segments from young male adult rats were perfused in situ with a control solution containing 0.02 mM pyridoxine (PN), 0.02 mM pyridoxal (PL), and 0.02 mM pyridoxamine (PM), followed by a test solution containing the same vitamin B-6 mixture and one of five fiber-rich test materials (cellulose, pectin, lignin, homogenized fresh carrot, or carrot homogenized after 10 min boiling) added at a concentration of 1-3%. The mean absorption rates of PL, PN, and PM from the control solution were, respectively, 3.66 +/- 0.23, 2.06 +/- 0.23, and 1.74 +/- 0.37 nmole/min/20 cm jejunal segment. There were no significant differences between the absorption rates of B-6 vitamers from control and test solutions containing cellulose, pectin, and lignin. The absorption rates of PM and PL were significantly depressed (P less than 0.05 and P less than 0.01, respectively) by the presence of fresh or cooked carrot. The absorption rate of PN in presence of cooked carrot was also decreased relative to the control value but the difference was only marginally significant (P less than 0.10). When the concentration of fresh carrot in the test solution was increased to 10% by weight and the perfusion rate was decreased from 1.91 to 0.49 ml/min in a second perfusion experiment, there was a significant increase in variability and the differences between absorption rates of the B-6 vitamers in control and test solutions were not statistically significant. The limited evidence of adverse effect of carrot on absorption of vitamin B-6 suggested the need for further clarification of the influence of dietary fiber in an unrefined state on the bioavailability of vitamin B-6.     

Spartina alterniflora loisel root structure and meiofaunal abundance

Meiofauna were collected from adjacent areas with and without Spartina alterniflora Loisel culms. Environmental complexity resulting from root structure cannot be determined by simply observing S. alterniflora culm distribution. There were no significant differences between the two areas with respect to root density or root sizes; however, the number of live roots was significantly higher in the area containing Spartina culms. Nematodes, the most abundant taxon were positively correlated with live root density. In contrast, the number of dead roots and harpacticoid copepods were higher in the area without culms. This study suggests that nematodes are positively associated with micro-oxygenated zones produced by live S. alterniflora roots. Other measures of biogenic structure, such as total root density or root size fractions are not important in affecting nematode abundance.     

Specific Inhibition of the Cyanide-insensitive Respiratory Pathway in Plant Mitochondria by Hydroxamic Acids

Hydroxamic acids, R-CONHOH, are inhibitors specific to the respiratory pathway through the alternate, cyanide-insensitive terminal oxidase of plant mitochondria. The nature of the R group in these compounds affects the concentration at which the hydroxamic acids are effective, but it appears that all hydroxamic acids inhibit if high enough concentrations are used. The benzhydroxamic acids are effective at relatively low concentrations; of these, the most effective are m-chlorobenzhydroxamic acid and m-iodobenzhydroxamic acid. The concentrations required for half-maximal inhibition of the alternate oxidase pathway in mung bean (Phaseolus aureus) mitochondria are 0.03 mm for m-chlorobenzhydroxamic acid and 0.02 mm for m-iodobenzhydroxamic acid. With skunk cabbage (Symplocarpus foetidus) mitochondria, the required concentrations are 0.16 for m-chlorobenzhydroxamic acid and 0.05 for m-iodobenzhydroxamic acid. At concentrations which inhibit completely the alternate oxidase pathway, these two compounds have no discernible effect on either the respiratory pathway through cytochrome oxidase, or on the energy coupling reactions of these mitochondria. These inhibitors make it possible to isolate the two respiratory pathways and study their mode of action separately. These inhibitors also enhance an electron paramagnetic resonance signal near g = 2 in anaerobic, submitochondrial particles from skunk cabbage, which appears to be specific to the alternate oxidase and thus provides a means for its assay.     

Changes in Ribonucleic Acid Fractions During Maturation of Mimosa Epicotyl Tissues

Total RNA and DNA of mimosa epicotyl tissues were extracted and the RNA fractionated into specific soluble RNAs (sRNAs) at different times during late germination. Epicotyls collected at each time contained qualitatively comparable meristematic and developing tissues, while mature tissues increased. Quantitative ratios of total RNA to DNA and total sRNAs to approximated ribosomal RNA (rRNA) varied consistently during development. Terminal nucleosides of sRNA did not vary in any consistent pattern through development. On the other hand, regular changes in quantitative ratios of specific sRNA groups were observed during development.