Influence of amino acids on nitrogen fixation ability and growth of Azospirillum spp

The utilization of amino acids for growth and their effects on nitrogen fixation differ greatly among the several strains of each species of Azospirillum spp. that were examined. A. brasiliense grew poorly or not at all on glutamate, aspartate, serine, or histidine as the sole nitrogen and carbon sources. Nitrogen fixation by most A. brasiliense strains was inhibited only slightly even by 10 mM concentrations of these amino acids. In contrast, A. lipoferum and A. amazonense grew very well on glutamate, aspartate, serine, or histidine as the sole nitrogen and carbon sources; nitrogen fixation, which was measured in the presence of malate or sucrose, was severely inhibited by these amino acids. It was concluded that growth on histidine as the sole source of nitrogen, carbon, and energy may be used for the taxonomic characterization of Azospirillum spp. and for the selective isolation of A. lipoferum. The different utilization of various amino acids by Azospirillum spp. may be important for their establishment in the rhizosphere and for their associative nitrogen fixation with plants. The physiological basis for the different utilization of glutamate by Azospirillum spp. was investigated further. A. brasiliense and A. lipoferum exhibited a high affinity for glutamate uptake (Km values for uptake were 8 and 40 microM, respectively); the Vmax was 6 times higher in A. lipoferum than in A. brasiliense. At high substrate concentrations (10 mM), the nonsaturable component of glutamate uptake was most active in A. lipoferum and A. amazonense.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prostaglandin I2 and the constricted maternal ovine placenta: effects of local infusion and placental age

We have tested the hypotheses that systemic responses to the infusion of prostaglandin I2 may have masked the ability of this substance to dilate the maternal placenta and that the inability of prostaglandin I2 to dilate the maternal near-term placenta may be a function of placental age. Regional blood flows were measured with radioactive microspheres. In 8 near-term sheep the control flows were measured and angiotensin II (AII) infusion was begun at 5 micrograms/min and continued for the duration of the experiments. At t = 15 min, regional blood flows were again measured. Prostaglandin I2 was then infused via a retrograde uterine arterial catheter at 10 micrograms/min. At t = 30 min, the flows were again measured. At this time the infusion of prostaglandin I2 was stopped and at t = 45 min the blood flows were measured for the last time. AII increased the resistance of all tissues examined. The blood pressure increased with AII and did not change thereafter. The non-placental uterine tissue served by the retrograde catheter dilated with prostaglandin I2. The placental tissue had an initial resistance of 59 +/- 6 mmHg.ml-1.min.g which increased to 98 +/- 22 mmHg.ml-1.min.g with the infusion of AII (P less than 0.05). This resistance remained constant at 82 +/- 19 mmHg.ml-1.min.g with the administration of prostaglandin I2 and did not change after prostaglandin I2 was removed. The local application of prostaglandin I2 in the presence of AII induced vasoconstriction caused vasodilatation in the nonplacental vessels but could not change the AII induced constriction in the placental vasculature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Zero-stress states of arteries

The no-load configuration of a living organ is, in general, not the zero-stress state. The difference can be revealed by cutting up an unloaded organ to such an extent that the stress becomes zero in the tissue everywhere. For the aorta, it is shown that the configuration of the zero-stress state differs considerably from being a cylindrical tube. It is, in fact, an open sector with opening angles varying along the arterial tree. This article presents data on the zero-stress state in the arteries of the rat in normal condition.     

Interactions of porphyrins with purified DNA and more highly organized structures

Studies of the solution properties of gold(III)tetrakis(4-N-methylpyridyl) porphine and its DNA binding characteristics have been conducted utilizing uv/vis absorption spectroscopy, circular dichroism (CD), Mossbauer spectroscopy, and temperature-jump relaxation techniques. These studies indicate that over the concentration range considered this water soluble gold(III) porphyrin does not aggregate, binds axial ligands only weakly with a preference for soft Lewis bases, and is capable of intercalation into nucleic acids of appropriate base pair content. The interaction of this and several other porphyrins with the synthetic polynucleotide poly(dA-dC).poly(dT-dG) has been studied. Spectroscopic signatures for intercalation were found for those derivatives not having axial ligands. Intercalation into chromatin in vitro can also occur with those porphyrins and metalloporphyrins which do not have axial ligands. Finally, studies utilizing microinjection techniques indicate that once within the cell, tetrakis(4-N-methylpyridyl)porphine tends to localize in the nucleus.     

Bacterial cellulases and saccharification of lignocellulosic materials

Five locally isolated bacterial strains produced extracellular cellulase enzymes, primarily CMCase, when grown on different natural and commercial cellulosic substrates. Extracellular CMCase and avicelase activity was higher with the strain CLS-32, a Cytophaga sp., compared to four other strains. The whole-cell preparations of these isolates were found to saccharify cellulosic substrates to reducing sugars. Maximum release of reducing sugar (5.75 mg ml⁻¹) was obtained with CLS-32 using sugar cane bagasse as growth and hydrolysis substrates.     

Microtubule and microfilament distribution and tubulin content in the cell cycle of Indian muntjac cells

Using DAPI, rabbit antitubulin antibody, FITC-labeled goat anti-rabbit IgG, and TRITC-phalloidin to stain individual cells, the microspectrophotometric analysis showed that three markers that represent the nucleus, microtubules (MT), and microfilaments (MF), respectively, could be recognized in individual cells without interference. The phase of the cell cycle was determined by DNA content. We found that in Indian muntjac (IM) cells, the amount of tubulin in G2 and M phases was about twice as much as that in G1 phase. In G2 cells, the cytoplasmic microtubule complex (CMTC) became denser than in G1 cells. The cytoplasmic MT extent in basically the same orientation as MF bundles in interphase. The regions where the MT is denser also have a denser MF distribution.     

Trypsin-sensitive neutralization site on VP1 of Theiler''s murine encephalomyelitis viruses.

We generated Theiler's murine encephalomyelitis virus mutants resistant to several neutralizing monoclonal antibodies (MAbs) having their epitopes near a trypsin cleavage site of VP1. Neutralization and Western blot (immunoblot) studies suggest that two of the MAbs have identical epitopes that partly overlap the epitope of a third MAb. Sequencing of RNA of the mutants localized the epitopes to a site near the carboxyl end of VP1. The limited diversity of nucleotide changes seen in the mutants and the immunodominance of the site suggest that the carboxyl end of VP1 may have an important function.