Formaldehyde-induced appearance of septate junctions between digestive vacuoles

Tissue biopsies from (1) some chronic inflammatory diseases, (2) a necrotic tumoral process, (3) normal human lymphatic ganglia, and (4) two congenital diseases of the adrenal cortex were selected for study. A block from each biopsy was fixed in glutaraldehyde-paraformaldehyde; a second block was fixed in 10% formaldehyde. In all cases septate junctions between digestive vacuoles did occur in phagocytic cells and some adrenal cortex cells fixed in formaldehyde. These junctions were similar to those reported recently for malakoplakia phagocytes. Consistently, they were not found to attach organelles other than lysosomes derivatives. Both phagocytes and adrenal cortex cells in the material fixed in glutaraldehyde-paraformaldehyde did not display adhesive specializations between digestive vacuoles. This suggests that the septate junctions described herein are artifactuous structures induced by formaldehyde. There is, however, a certain degree of specificity of cells having the capability of developing these septate junctions. It is assumed that the coating material of digestive organelles in phogocytes and some other cells would be responsible for both cell specificity and organelle specificity of the formaldehyde-induced septate junctions.     

Stringent response and initiation of secondary metabolism in Streptomyces clavuligerus

Cephalosporin biosynthetic activity and extracellular protease production increased during growth of Streptomyces clavuligerus in defined medium, while the level of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) remained very low and stable. Cephalosporin biosynthesis (measured in resting cell systems) was initiated during early exponential growth in complex media, without appreciable change in the small ppGpp pool. Nutritional shift-down induced by withdrawal of Casamino acids caused a transient increase in ppGpp and a reduction of RNA accumulation. The increase in ppGpp was small in very young cultures, but increased as the culture aged. Twenty-seven spontaneous thiostrepton-resistant mutants were isolated and partially characterized. Most of them had a reduced ppGpp-forming ability and gave normal titres of cephalosporin. However, in complex medium, some mutants did not produce cephalosporins or extracellular protease, whereas others overproduced cephalosporins. The results indicate that, in S. clavuligerus, there is no obligatory relationship between the initiation of secondary metabolism and the stringent response.     

Cloning, sequencing, and mutational analysis of the Bradyrhizobium japonicum fumC-like gene: evidence for the existence of two different fumarases.

The Bradyrhizobium japonicum fumarase gene (fumC-like) was cloned and sequenced, and a fumC deletion mutant was constructed. This mutant had a Nod+ Fix+ phenotype in symbiosis with the host plant, soybean, and growth in minimal medium with fumarate as sole carbon source was also not affected. The cloned B. japonicum fumC gene fully complemented an Escherichia coli Fum- mutant, strain JH400, for growth in minimal medium with fumarate. The predicted amino acid sequence of the FumC protein showed strong similarity to the E. coli FumC protein, Bacillus subtilis CitG protein, Saccharomyces cerevisiae Fum1 protein, and the mammalian fumarases. The B. japonicum FumC protein accounted for about 40% of the total fumarase activity in aerobically grown cells. The remaining 60% was ascribed to a temperature-labile fumarase. These data suggest that B. japonicum possesses two different fumarase isoenzymes, one of which is encoded by fumC. Besides E. coli, which has three fumarases, B. japonicum is thus the second bacterium for which there is genetic evidence for the existence of more than one fumarase.     

Changes in force and calcium sensitivity in the developing avian heart.

The aim of this study was to characterize the development of the contractile properties of intact and chemically skinned muscle from chicken heart and to compare these characteristics with those of developing mammalian heart reported by others. Small trabeculae were dissected from left ventricles of Arbor Acre chickens between embryonic day 7 and young adulthood (7 weeks post-hatching). At all ages, increasing extracellular calcium (0.45-3.6 mM) progressively increased twitch force of electrically stimulated trabeculae. Twitch force at 1.8 mM extracellular calcium, normalized to cross-sectional area, increased to a maximum at 1 day post-hatching, remained constant through 3 weeks post-hatching, but then decreased at 7 weeks post-hatching. The maximal calcium-activated force of trabeculae chemically skinned with Triton X-100 detergent increased to a maximum 2 days before the time of hatching and was not significantly changed up to 7 weeks post-hatching. Over the ages studied, average twitch force in 1.8 mM calcium was between 26 and 66% of maximal calcium-activated force after skinning, suggesting that the contractile apparatus is not fully activated during the twitch in normal Ringer. In skinned trabeculae, the calcium sensitivity of the contractile apparatus was higher in the embryo than in the young adult. These age-dependent changes in calcium sensitivity are correlated with isoform switching in troponin T. A decrease in pH from 7.0 to 6.5 decreased the calcium sensitivity of the contractile apparatus to a greater degree in skinned trabeculae from young adult hearts than in those from embryonic hearts. This change in susceptibility to acidosis is temporally associated with isoform switching in troponin I.(ABSTRACT TRUNCATED AT 250 WORDS)     

A limnological reconnaissance of Lake Tebenquiche,Salar de Atacama,Chile

A number of expeditions to the area of Salar de Atacama, Chile, 68° 15'W, 20° 30'S, have involved studies of the biological and chemical features of Lake Tebenquiche, situated in the interior of the salar. Chemically, Tebenquiche is hypersaline, with practically anoxic waters dominated by sodium and chloride ions but with high concentrations of sulphate also. The lake is surrounded and invaded by macrophytes, dominated by Scirpus olmeyi and Juncus, which provide organic material for the formation of bacterial mats. The fauna of limnetic crustaceans is almost exclusively of Artemia salina. The most important genera of bacteria are: Marinomonas, Halobacterium, Acinetobacter and the sulphur reductors Vibrio and Bacillus. The Cyanobacteria are represented exclusively by Oscillatoria.     

Kinetics of a model of autocatalysis, coupling of a reaction in which the enzyme acts on one of its substrates.

A global kinetic analysis is presented of a model of an enzyme autocatalytic process, to which a reaction is coupled, in which the enzyme acts upon one of its substrates. The kinetic equations of both the transient phase and the steady state are derived for this mechanism. In addition, we determine the corresponding kinetic equations for several particular cases which are characterized by certain relations between the rate constants. Finally, a kinetic data analysis is proposed for one of these particular cases. It can easily be extended to any of the other cases.     

Sequence and characterization of Bacillus subtilis CheW.

A Bacillus subtilis open reading frame (ORF) encoding a predicted polypeptide of 156 amino acids was subcloned and sequenced. The polypeptide was found to be homologous to CheW of Escherichia coli, sharing 28.6% amino acid identity. The ORF was verified by using a bacteriophage T7 expression system in E. coli. The gene was inactivated by insertion of a nonpolor chloramphenicol acetyltransferase cassette in its N-terminal region. In the absence of chemoeffectors, the mutant displayed a smooth swimming bias, with some tumbling. The CheW- mutant was defective on swarm plates but was complemented by a plasmid that expressed wild type CheW. Addition of attractant or repellent to the CheW- mutant resulted in transient smooth swimming or tumbling, respectively. However, capillary assays revealed that chemotaxis was substantially impaired in the mutant strain.     

Naturally occurring benzodiazepines in human milk

The presence of benzodiazepine-like molecules was detected radioimmunologically in the plasma and milk of 12 women and in the plasma of 9 men. All subjects were non-users of benzodiazepines. The concentration of these biological materials expressed as diazepam equivalents per mL amounted to 2.54 +/- 0.74 ng in male plasma; to 2.20 +/- 0.35 ng in female plasma and to 1.91 +/- 0.54 ng in milk. Further investigation of the active compounds in milk permitted the unequivocal identification of diazepam, both free and bound to a presumably protein carrier and, at least, three more benzodiazepine-like molecules. Their origin either from dietary sources or as a result of endogenous biosynthesis is still unclear.     

Thyroid hormones control lipid composition and membrane fluidity of skeletal muscle sarcolemma.

Sarcolemma membrane lipid phase of skeletal muscles of hyperthyroid animals was compared to that of control (euthyroid) ones. Hyperthyroidism caused 15% decrease in cholesterol and 70% increase in the phospholipid content of the membrane. This was accompanied by the alterations in proportions between individual phospholipid classes, and was followed by changes in the composition of phospholipid fatty acids. The calculated fatty acid unsaturation index was higher for membrane lipid phase of hyperthyroid animals than of euthyroid ones. Thyroxine-induced alterations in the lipid composition of sarcolemma caused changes in the membrane fluidity and the activity of calmodulin-stimulated (Ca(2+)-Mg(2+)-ATPase. Measurements of the steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene indicated that the lipid phase transition of membrane vesicles occurred at 25.9 degrees C and at 28.9 degrees C for preparations isolated from hyperthyroid and euthyroid rabbits, respectively. Arrhenius plot break-point temperature for CaM-stimulated (Ca(2+)-Mg(2+)-ATPase activity was lower in membrane preparations isolated from hyperthyroid (26.9 degrees C) than from euthyroid ones (30.0 degrees C). Thus, the increase of the membrane fluidity presumably caused that the enzyme was characterized by the lower activation energy value. This phenomenon may be viewed as a supplementary mechanism for activation of the enzyme by thyroid hormones to previously reported elevation of the amount of (Ca(2+)-Mg(2+)-ATPase protein exerted by hyperthyroidism (Famulski et al. (1988) Eur. J. Biochem., 171, 363-368; Famulski and Wrzosek (1988) in The Ion Pumps-Structure, Function and Regulation (Stein, W.D., ed.), pp. 355-360, Alan R. Liss, New York).