PubMed · 11103460
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P G Collins, P Avouris. 2000. Nanotubes for electronics.. https://doi.org/10.1038/scientificamerican1200-62
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Pectobacterium brasiliense 1692 (Pbr1692) is a necrotrophic pathogen that infects many crops such as potatoes and ornamental plants and derives nutrients from degraded plant tissue. Previous studies have identified Pbr1692 genes required for ecological fitness and virulence, however there is a lack of information on nutrient utilization in Pbr1692. Carbon source utilization profiling in Pbr1692 could provide a platform to decipher its metabolic flexibility and adaptation. This study assessed the nutrient utilization of Pbr1692 in different carbon sources, using Biolog Phenotypic Microarray (PM). An array of carbon sources utilized by Pbr1692 were identified, 32 carbohydrates and 8 carboxylic acids were among the preferred carbon nutrients utilized by Pbr1692. The PM results also revealed that the citric acid cycle, amino acid metabolism, and pentose phosphate metabolic pathways might be used to produce energy for Pbr1692. In addition, growth of Pbr1692 cells in minimal medium supplemented with citric acid, glucose, and aspartic acid retained the typical rod shape, suggesting that nutrient variation did not influence Pbr1692 cell morphology adaptation. This study provides an understanding on the adaptation of Pbr1692 and lays a foundation for understanding carbon metabolism of Pbr1692.
3',4'-Anhydroadenosylcobalamin (anAdoCbl) is an analogue of the adenosylcobalamin (AdoCbl) coenzyme (Magnusson, O.Th., and Frey, P. A. (2000) J. Am. Chem. Soc. 122, 8807-8813). This compound supports activity for diol dehydrase at 0.02% of that observed with AdoCbl. In a side reaction, however, anAdoCbl induces suicide inactivation by an electron-transfer mechanism. Homolytic cleavage of the Co-C bond of anAdoCbl at the active site of diol dehydrase was observed by spectrophotometric detection of cob(II)alamin. Anaerobic conversion of enzyme bound cob(II)alamin to cob(III)alamin, both in the absence and presence of substrate, indicates that the coenzyme derived 5'-deoxy-3',4'-anhydroadenosine-5'-yl serves as the oxidizing agent. This hypothesis is supported by the stoichiometric formation of 3',5'-dideoxyadenosine-4',5'-ene as the nucleoside cleavage product, as determined by high-performance liquid chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopy. Experiments performed in deuterium oxide show that a single solvent exchangeable proton is incorporated into the product. These data are consistent with the intermediate formation of a transient allylic anion formed after one electron transfer from cob(II)alamin to the allylic 5'-deoxy-3',4'-anhydroadenosyl radical. Selective protonation at C3' was demonstrated by spectroscopic characterization of the purified product. This study provides an example of suicide inactivation of a radical enzyme brought about by a side reaction of an analogue of the radical intermediate.
Most plants are known as C3 plants because the first product of photosynthetic CO2 fixation is a three-carbon compound. C4 plants, which use an alternative pathway in which the first product is a four-carbon compound, have evolved independently many times and are found in at least 18 families. In addition to differences in their biochemistry, photosynthetic organs of C4 plants show alterations in their anatomy and ultrastructure. Little is known about whether the biochemical or anatomical characteristics of C4 photosynthesis evolved first. Here we report that tobacco, a typical C3 plant, shows characteristics of C4 photosynthesis in cells of stems and petioles that surround the xylem and phloem, and that these cells are supplied with carbon for photosynthesis from the vascular system and not from stomata. These photosynthetic cells possess high activities of enzymes characteristic of C4 photosynthesis, which allow the decarboxylation of four-carbon organic acids from the xylem and phloem, thus releasing CO2 for photosynthesis. These biochemical characteristics of C4 photosynthesis in cells around the vascular bundles of stems of C3 plants might explain why C4 photosynthesis has evolved independently many times.