Effects of fluoride on growth, reproduction and survival in Daphnia magna

The effects of waterborne fluoride (NaF) on growth, reproduction and survival in Daphnia magna were studied from subnormal to toxic concentrations in hard reconstituted water. The 24- and 48-hr EC50S for immobilization were 205 and 98 mg F (fluoride) 1(-1). Median survival times for fed and unfed Daphnia were reduced at concentrations of F above 8.9 and 10 mg F1(-1), respectively. Growth, determined as body length after 7 and 21 days, was partially inhibited at all concentrations above 3.7 mg F1(-1). Parthenogenetic reproduction was stimulated by all concentrations (dilution factor 0.5) between 0.45 X 10(-3) mg F1(-1) and 3.7 mg F1(-1) and inhibited by all concentrations above 3.7 mg F1(-1), compared to the control with no waterborne fluoride. The highest concentration with a reproduction (number of live progeny/live female) equivalent to the control after 21 days was 4.4 mg F1(-1). However, a progressive decline in reproduction between 14 and 21 days indicates a slight long-term inhibition above 0.58 mg F1(-1). The "safe" concentration equivalent to the geometric mean of NOEC or MATC for D. magna in hard water is 4.4 mg F1(-1), derived as ZEP, the Zero Equivalent Point, for reproduction after 21 days.     

Possible mitochondrial involvement in mechanism of cytoplasmic male sterility in maize (Zea mays L.)

The mechanism of cytoplasmic male sterility was investigated in maize by isolating mitochondria from seedlings and various anther stages and analyzing cytochrome oxidase and succinic dehydrogenase biochemically and electrophoretically. Sterile anthers exhibited a lack of biochemical activity and fewer isozymatic bands for cytochrome oxidase. No apparent differences were detected biochemically or electrophoretically between fertile and sterile anthers for succinate dehydrogenase.     

Isolation and properties of Bacillus brevis mutants unable to produce tyrocidine.

Mutants of Bacillus brevis ATCC 10068 were isolated which produced less than 1/100 of the amount of tyrocidine produced by the parent strain. These mutants produced spores at the same frequency and which were as resistant to heating at 80 degrees C for up to 3 h as were those produced by the parent strain. A partially purified tyrocidine synthetase from strain ATCC 10068 catalyzed [32P]PPi-ATP exchange reactions dependent on added tyrocidine-constituent amino acids. These activities were separated into three groups (I, II, and III) by fractionation on an Ultrogel AcA34 column. Each group was similar to one of the three components (heavy, intermediate, and light, respectively) found previously for strain ATCC 8185 except that glutamate-dependent activity was not detected in the group I activities and some amino acyl-tRNA synthetase activities were associated with the group III activities. Some of the mutants were shown to have defective tyrocidine synthetase enzymes. Mutant BH30 was defective in two of the group II amino acid-dependent [32P]PPi-ATP exchange reactions, mutant BH16 was defective in one of the group I and one of the group II reactions, and mutant BH34 had alterations to activities in all of the groups. It is unlikely that any of these mutants could synthesise tyrocidine. We conclude that tyrocidine is not involved in either the sporulation process or the resistance of spores of B. brevis ATCC 10068 to heating at 80 degrees C for up to 3 h.     

Sexual development of patients with isochromosomes for the long arm of the X chromosome

Summary The sexual development of 14 girls with non-mosaic monocentric 46,X,iXq karyotype was studied. Seven out of eight girls were found to have immature secondary sexual characteristics and amenorrhoea, a finding greatly contrasting with that in Triplo-X girls. The relative ineffectiveness of the isochromosome Xq in maintaining fertility may be due to the absence of one short arm, which probably also carries a gonadal determinant. Alternatively, the presence of two inactivation sites on one isochromosome may render the gonadal determinants inactive at an important stage in gonadal development.     

Helical channels in crystals of gramicidin A and of a cesium--gramicidin A complex: an x-ray diffraction study.

X-ray crystallographic studies of gramicidin A crystallized from methanol (P2₁) and ethanol (P2₁2₁2₁), and of a Cs⁺ gramicidin A complex crystallized from methanol (P222₁, P2₁2₁2 or P2₁2₁2₁) are reported here. The asymmetric unit consists of two molecules of gramicidin A in the native crystals and four molecules in the cesium complex crystal. Patterson analyses show that gramicidin A in these crystals forms a cylindrical helical channel. In the two types of native gramicidin crystals, the diameter of this channel is about 5 å and its length is about 32 å. Cesium ions are bound inside this channel in crystals of the cesium-gramicidin A complex. The channel in this complex is considerably shorter (26 Å) and wider (6·8Å) than in the native forms. The Patterson maps of these three crystal forms are compatible with either the single-stranded β-helix (Urry, 1971) or the double-stranded parallel or anti-parallel, β-helix (Veatch et al., 1974).     

Prolactin modifies the prostaglandin synthesis, prolactin binding and fluidity of mouse liver membranes

The objective of these studies was to determine if prolactin, known to induce its own receptors, alters the prostaglandin (PG) synthesis which could, in turn, modify the fluidity of the membrane and thus alter the functionality of prolactin receptors. Adult male C₃H mice were injected subcutaneously with 100 μg of oPRL every 4 h for 0, 24 or 48 h and sacrificed 8 h after receiving the last injection. Liver 100,000 × $\text{g}$ membrane pellets were used in the measurement of these parameters. The amount of binding of prolactin to these membranes increased with the duration of injections, the values being 179 and 244% of control values after 24 and 48 h of injections, respectively. The amounts of PGF_2α and PGE synthesized also increased after these injections, the values being 127 and 270% of control for PGF_2α and 634 and 695% of control values for PGE after 24 and 48 h of injections, respectively. Fluorescence polarization, an index of microviscosity, was decreased by 14 and 20% after 24 and 48 h of PRL administration, respectively. Previous studies have demonstrated simultaneous in vitro effects of prostaglandin on both prolactin receptors and membrane fluidity. The current data are in agreement with those observations and suggest that prolactin may modulate its own receptor by increasing the fluidity of the membrane in which it exists by alterations within the PG cascade. Such biochemical changes may then modify existing restraints and allow the hormone receptor to assume a more functional configuration.     

Hepatotropin mRNA expression in human foetal liver development and in liver regeneration

A 569 bp probe against the β-chain of hepatotropin was used to examine expression of RNA for this growth factor in human adult and foetal liver, foetal kidney and pancreas, and rat liver after partial hepatectomy. Low level expression of a 6kb RNA occurred in human adult and normal rat liver. 70% hepatectomy increased expression, peaking at 10 h and returning to near normal levels 24 h after resection. The 6 kb band was strongly expressed in human foetal liver, as compared with adult, but not in foetal kidney or pancreas, suggesting a major role for hepatotropin in both foetal development and regeneration of the liver.     

Indium-111 autologous leucocyte scanning: comparison with radiology for imaging the colon in inflammatory bowel disease.

Indium-111 autologous leucocyte scanning was compared with barium enema for assessing the extent of colonic disease in Crohn''s colitis and ulcerative colitis. Scanning was shown to be as accurate as conventional radiology in colitis, reliably distinguishing active from inactive disease. The results suggest that 111In-leucocyte scanning is an accurate, non-invasive, alternative technique for imaging the extent of disease in colitis.     

Regulation of lysine- and lysine-plus-threonine-inhibitable aspartokinases in Bacillus brevis.

Further studies on the expression of the two aspartokinase activities in Bacillus bovis are presented. Aspartokinase I (previously shown to be inhibited and repressed by lysine) was found to be repressed by diaminopimelate in the wild-type strain. However, in a mutant unable to convert diaminopimelate to lysine, starvation for lysine resulted in an increase in aspartokinase I activity. Thus, lysine itself or an immediate metabolite was the true effector of repression. Aspartokinase II (previously shown to be inhibited by lysine plus threonine) was repressed by threonine. Studies with the parent strain and auxotrophs inidicated that only threonine or an immediate metabolite of threonine was involved in this repression. Methionine and isoleucine were not effectors of any of the detected aspartokinase activities. Apart from inhibition and repression controls, a third as yet undefined regulatory mechanism operated to decrease the levels of both aspartokinases as growth declined, even in mutants in which repression control was absent. In thiosine-resistant, lysine-excreting mutants with elevated levels of aspartokinase, the increase in activity could always be attributed to one enzyme or the other, never both. The existence of separate structural genes for each aspartokinase is therefore suggested.