Compartmentalisation of nitrogenase in a non-heterocystous cyanobacterium: Trichodesmium contortum

Abstract In Trichodesmium contortum , nitrogenase was detected in only a limited number (about 10%) of microscopically distinguishable, consecutively arranged cells in central regions of the trichomes. Cells with nitrogenase also contained the photosystem II associated pigment phycoerythrin. These cells were not distinguishable from other cells on a structural basis, but were clearly visible at low magnification microscopy as all in the zone were more compact and shorter than those on either side. The compartmentalisation of nitrogenase into a chain of cells and in a possibly photosynthetic environment represents a previously undescribed phenomenon. The nitrogenase containing cells apparently perform the O₂ protective function of heterocysts yet are different in several aspects.     

Detection of Aldehydes and Their Conjugated Hydroperox Ydiene Precursors in Thermally-Stressed Culinary Oils and Fats: Investigations Using High Resolution Proton Nmr Spectroscopy

High field (400 and 600 MHz) proton NMR spectroscopy has been employed to investigate the thermally-induced autoxidation of glycerol-bound polyunsaturated fatty acids present in intact culinary frying oils and fats. Heating of these materials at 180°C for periods of 30, 60 and 90 min. generated a variety of peroxidation products, notably aldehydes (alkanals, trans-2-alkenals and alka-2, 4-dienals) and their conjugated hydroperoxydiene precursors. Since such aldehydes appear to be absorbed into the systemic circulation from the gut in vivo, the toxicological significance of their production during standard frying practices is discussed.     

Strategies for signal amplification in nucleic acid detection

Many aspects of molecular genetics necessitate the detection of nucleic acid sequences. Current approaches involving target amplification (in situ PCR, Primed in situ Labeling, Self-Sustained Sequence Replication, Strand Displacement Amplification), probe amplification (Ligase Chain Reaction, Padlock Probes, Rolling Circle Amplification) and signal amplification (Tyramide Signal Amplification, Branched DNA Amplification) are summarized in the present review, together with their advantages and limitations.     

Multiple mechanisms contribute to myenteric plexus ablation induced by benzalkonium chloride in the guinea-pig ileum

Ablation of rat myenteric plexus with benzalkonium chloride has provided a model of intestinal aganglionosis, but the degenerative responses are not well understood. We examined the effects of this detergent on neurons and glia, including expression of c-Myc, c-Jun, JunB, and c-Fos, and on immunocytes in the guinea-pig ileum. Benzalkonium chloride (0.1%) or saline was applied to the serosal surface of distal ileum. Tissues were analyzed 2, 3, or 7 days later and compared with cyclosporine-treated and untreated animals. More than 90% of myenteric neurons were destroyed in ileal segments 3–7 days after benzalkonium-chloride treatment. Glia withdrew processes from around neurons after 2 days and were mostly gone after 3 days. Neuronal c-Myc began to disappear while c-Fos, c-Jun, and JunB were evident in some neuronal nuclei after 2 or 3 days. After 3 days, widespread apoptosis was evident in the myenteric plexus. Populations of T cells, B cells, and macrophage-like cells in untreated and saline-treated myenteric plexuses were substantially increased 3 and 7 days after benzalkonium-chloride treatment. Cyclosporine delayed significant neuronal loss. We conclude that a variety of degenerative mechanisms may be active in this model, including an immune response which may actively contribute to tissue destruction. Received: 13 September 1996 / Accepted: 20 January 1997     

Purification and characterization of chick intestine brush border membrane Effects of 1α(OH) vitamin D3 treatment

A new technique has been developed for the isolation of membrane vesicles from the vitamin D-deficient and vitamin D-treated chick intestinal brush border membrane. The technique involves removal of nuclei from a low speed pellet by discontinuous sucrose gradient centrifugation. The resulting intact brush borders are then homogenized in 0.5 M Tris and the membrane fragments purified on a glycerol gradient. This preparation represents a 20-fold purification of the brush border marker sucrase. After 1α-hydroxyvitamin D₃ treatment there is a significant increase in membrane phospholipid phosphorous, an alteration in the fatty acid composition of the phosphatidylcholine fraction of membrane phospholipid, and a decrease in sucrase specific activity.     

The biology and physiology of alga-invertebrate symbioses. III. In situ measurements of photosynthesis and calcification in some hermatypic corals

In situ measurements of the rates of photosynthesis and calcification in three species of hermatypic corals were made at Eilat, in the Gulf of Aqaba, Red Sea. Experiments were made at 5, 20 and 35 m depth under unusually poor conditions of submarine illumination for the region, and at the relatively low water temperature (21°C) for coral growth which prevails there all year. Estimates of photosynthetic rates by both the ¹⁴C and oxygen methods indicated that the ¹⁴C method does measure gross photosynthesis in these organisms even at, and below, light compensation points. Substantial rates of carbon fixation in Acropora and Millepora show that, even under bad conditions, these organisms could survive autotrophically to at least 10 m depth, as also could the massive coral Goniastrea although this had much lower photosynthetic rates under the same conditions, compensated for by a much lower respiratory rate than the other two corals.Calcification rates were variable but showed a considerable increase in light as compared with the dark in all three species, and the rates did not decrease with depth as much as might have been anticipated from the reduction in photosynthesis and ambient light energy. Photosynthetic and calcification rates were similar to those reported for similar organisms both in the Caribbean and on the Great Barrier Reef.     

Biochemical Characterization of Molybdenum-Cofactor in a Cyanobacterium, Nostoc muscorum

Cell-free extracts of nitrate-grown Nostoc muscorum containnitrate reductase and molybdenum-cofactor activities. Whilenitrate reductase activity is associated with the paniculatefraction, cofactor activity is found predominantly in the solublefraction. This activity was distributed between two pools. Inone pool, the molybdenumcofactor is associated with a carrier(protein) of approximately 30,000 Da with an S_{20, w} between2.3 and 2.5. The carrier-bound cofactor is non-dialyzable andis found along with the major proteins during filtration inSephadex G-25 and G-100. The second pool contains free or unboundcofactor. It is separated from soluble proteins by dialysiswith a membrane with a pore-size of 10 to 15 kDa. However, itis retained with a membrane with a pore size of 1 kDa. It isin the included volume during chromatography through SephadexG-25. Its molecular mass is estimated to be between 1,000 and5,000 Da. The molybdenum content was proportional to cofactoractivity in both pools. Reducing agents increased cofactor activity.However, activity in both pools was sensitive to heat, acid,and oxidative treatments. The carrier protein appears to givesome protection. ¹Fulbright Scholar from Department of Biological Sciences, R.D. University, Jabalpur-482001, India. To whom reprint requestsshould be addressed. (Received June 22, 1987; Accepted August 21, 1987)     

Distinct phases of the fluorescence response of the lipophilic probe N-phenyl-1-naphthylamine in intact cells and membrane vesicles of Escherichia coli

The fluorescence of the lipophilic prbe N-phenyl-1-naphthylamine (NPN) bound to intact cells of Escherichia coli is quenched by the addition of glucose, succinate, -lactate, pyruvate, formate and glycerol. Partial recovery of fluorescence occurs on anaerobiosis. Use of mutants with defects in the ATP synthase or the respiratory chain show that quenching of fluorescence may be energized either by ATP hydrolysis or by substrate oxidation through the respiratory chain. Permeabilization of the outer membrane by treatment of intact cells with EDTA, or use of a mutant with an outer membrane permeable to lipophilic substances, results in a more rapid binding of NPN and in a decrease in quenching observed on substrate addition. NPN binds rapidly to everted membrane vesicles, but does not respond to membrane energization. It is proposed that inner membrane energization in intact cells alters the binding or environment of NPN in the outer membrane. The fluorescence recovery which occurs on anaerobiosis has two components. One component represents a reversal of the changes which occur on membrane energization. The other component of the fluorescence change is insensitive to the uncoupler CCCP and resembles the behaviour of NPN with everted membrane vesicles. It is suggested that a portion of the fluorescence events seen with NPN involves a response of the probe to changes in the inner membrane.