Presence of Epstein-Barr virus receptors, but absence of virus penetration, in cells of an Epstein-Barr virus genome-negative human lymphoblastoid T line (Molt 4).

This paper reports a unique type of interaction of Epstein-Barr virus (EBV) with an EBV receptor-positive, genome-negative human lymphoid T cell line (Molt 4), which can be summarized as follows. Although Molt 4 cells express receptors for EBV, they appear to block the penetration of this virus. These observations are derived from combined studies with immunofluorescence and electron microscopy. It is possible that T cell lines bearing receptors for EBV may express such a control on virus penetration.     

Studies on plating efficiency and estimation of viability of suspensions of Paracoccidioides brasiliensis yeast cells

Mild sonication was used to obtain single cell suspensions of Paracoccidioides brasiliensis. These cells were intact by microscopic criteria. Direct cell counts in a given inoculum and colony formation on various media were used to determine plating efficiency. Sonicated and nonsonicated cell suspensions were used to study plating efficiency and to estimate viability by means of vital dyes. Methylene blue, Erythrosin B, and Janus green were unreliable when used with P. brasiliensis, but vital dyes were accurate when tested with Candida albicans.Acridine orange gave more meaningful results of viability. Estimates of viability, however, changed significantly as a result of relatively minor alterations in the composition of the suspending medium.In initial experiments, the plating efficiency of P. brasiliensis was dismally low. It descended abruptly with increasing dilution of inoculum. Efficiency was much improved if horse serum was added to brain heart infusion plates or if glucose glycine yeast extract (GGY) plates were incubated at room temperature and mycelial colonies were counted. With the technique we report, current plating efficiency of sonicated suspensions is of the order of 25 %. Our results and procedures have an important bearing upon those studies concerned with in vitro killing of P. brasiliensis in suspensions or with isolating this fungus from clinical or environmental specimens.     

The effect of glucagon on the kinetics of hepatic mitochondrial calcium uptake

Summary Previous work by this and other laboratories has shown that glucagon administration stimulates calcium uptake by subsequently isolated hepatic mitochondria. This stimulation of hepatic mitochondrial Ca²⁺ uptake byin vivo administration of glucagon was further characterized in the present report. Maximal stimulation of mitochondrial Ca²⁺ accumulation was achieved between 6–10 min after the intravenous injection of glucagon into intact rats. Under control conditions, Ca²⁺ uptake was inhibited by the presence of Mg²⁺ in the incubation medium. Glucagon treatment, however, appeared to obliterate the observed inhibition by Mg²⁺ of mitochondrial Ca²⁺ uptake. Kinetic experiments revealed the usual sigmoidicity associated with initial velocity curves for mitochondrial calcium uptake. Glucagon treatment did not alter this sigmoidal relationship. Glucagon treatment significantly increased the V_max for Ca²⁺ uptake from 292±22 to 377±34 nmoles Ca²⁺ /min per mg protein (n=8) but did not affect the K_0.5, (6.5–8.6 μM). Since the major kinetic change in mitochondrial Ca²⁺ uptake evoked by glucagon is an increase in V_max, the enhancement mechanism is likely to be an increase either in the number of active transport sites available to Ca²⁺ or in the rate of Ca²⁺ carrier movement across the mitochondrial membranes.     

Isolation and properties of crystalline ferredoxin from lactuca sativa

Lettuce ferredoxin has been purified to homogeneity, with a yield of 18 mg/kg of denerved leaves. It crystallizes in magnificent needles, often clustered in broom-like sheaves. The absorption spectrum showed maxima at 460, 422, 330 and 274 nm,with a ratio A₄₂₂/A₂₇₄, of 0.46. The mM absorption coefficient was 9.74 at 422 nm, and 21.62 at 274 nm. This ferredoxin showed a pI = 4.7 and an E′₀ = ?425 mV (at pH = 7.7). MWs of 12 400, 11480 and 13000 were obtained by sucrose gradient centrifugation, and on the basis of the amino acid composition and the iron content, respectively, with an average of 12 300. The amino acid analysis showed the existence of one methionine residue per mole, with 105 amino acid residues. There are two iron atoms and two labile sulfide groups per mole; 4 half-cystine residues were found by performic acid oxidation, and 5 cysteine groups when determined by titration with pHMB. The native protein is not fixed on thiol-Sepharose 4B, but it is quantitatively retained after incubation with 8 M urea. Lettuce ferredoxin showed a 62, 58 and 78% effectiveness with the spinach ferredoxin-NADP reductase, nitrite reductase and fructose-1,6-diphosphatase (FDPase), respectively, when compared with the spinach ferredoxin. This different behaviour of both ferredoxins is joined to genetic-structural relationships, and suggests that the role of ferredoxin in FDPase activation is more sophisticated than that of a mere nonspecific reductant.     

Pre-induction priming of the uterine cervix with oral prostaglandin E2 and a placebo

A double blind study was undertaken to determine the effectiveness or oral prostaglandin E2 as a means of improving the pelvic score prior to induction of labour. 48 patients who were greater than 37 were gestation and who had Bishop scores of less than 6 entered the study. Ten tablets were given on an hourly regime. Of 25 patients in the prostaglandin group, 17 were considered successes (68.0%), whereas of 23 patients who received a placebo, 9 were successes (39.1%). No adverse effects were recorded. Prostaglandin E2 is therefore considered a safe and effective method for priming the unfavourable cervix prior to induction of labour.     

Characterization by photoaffinity labeling of a steroid binding protein in rat liver plasma membrane

Summary The mechanism of steroid uptake by the cell remains controversial. [³H]R5020 was utilized to characterize by photoaffinity labeling the steroid binding site in plasma membrane. This binding was saturable, reversible and had one type of binding site (K _d = 33 ± 4 nm, B _max = 32 ± 2 pmol/mg). [³H]R5020 could be prevented from binding by a variety of steroids (cortisol, progesterone, deoxycorticosterone, and levonorgestrel); estradiol did not have affinity for this binding site. The kinetics of R5020 photoactivation was time dependent and saturable. SDS-PAGE showed a specific band which corresponded to a 53-kDa peptide. The sucrose density gradient analysis has revealed the existence of a protein with a sedimentation coefficient of 3.6 ± 0.2 S. This polypeptide shows different characteristics than cytosolic steroid receptor or serum steroid binding proteins. This binding protein could correspond to the steroid binding site previously found in the plasma membrane.This work was supported by grants PB85-0461 from the Comisión Asesora de Investigatión Científica y Técnica and PGV-8612 from the Departamento de Educatión, Universidades e Investigation del Gobierno Vasco. We thank Roussel-Uclaf (France) for the nonradioactive RU-steroids kindly provided.     

Cell growth and water relations of the halophyte,Atriplex nummularia L., in response to NaCl

Summary Growth reduction or cessation is an initial response of Atriplex nummularia L. cells to NaCl. However, A. nummularia L. cells that are adapted to 342 and 428 mM NaCl are capable of sustained growth in the presence of salt. Cells that are adapted to NaCl exhibit a reduced rate of division compared to unadapted cells. Unlike salt adapted cells of the glycophyte Nicotiana tabacum L., A. nummularia L. cells do not exhibit reduced rate of cell expansion after adaptation. However, the cell expansion rate of unadapted A. nummularia L. cells is considerably slower than that of unadapted glycophyte cells and this normally low rate of cell expansion may contribute to the enhanced capacity of the halophyte to tolerate salt. Turgor of NaCl adapted cells was equivalent to unadapted cells indicating that the cells of the halophyte do not respond to salt by osmotic over adjustment as reported for the glycophyte tobacco (Binzel et al. 1985, Plant Physiol. 79:118–125).     

Effects of storage on germination ofDioscorea composita (Dioscoreaceae) seeds

Effects of storage were tested on germination ofDioscorea composita (Dioscoreaceae) seeds. Freshly collected seeds and seeds stored at 25°C in paper bags from 1 to 11 mo or for 4 and 5 yr were used in most of the experiments. Seeds were tested for germination at 20, 25, 30, 35, 25–20, and 25–35°C in white light and in darkness. Initiation of germination was delayed in freshly harvested seeds, and dormancy was reduced in seeds stored for about 9 mo. Viability of the seeds decreased after 4 and 5 yr of storage.     

Solubilization of collagen-tailed molecular forms of acetylcholinesterase from several brain areas in different vertebrate species

The relative efficiency of a buffered medium containing a high salt concentration and EDTA as a means to solubilize collagen-tailed molecular forms of acetylcholinesterase has been examined in four brain areas of several species belonging to different vertebrate classes. This extraction procedure has proved successful in most cases, with the yield of tailed enzyme varying between less than 1 and 26% of the total tissue activity. The solubilization values are consistently higher in more primitive vertebrates than in mammals and, for a given species, are usually lower in the telencephalon than in other brain structures. Our results confirm that the vertebrate central nervous system contains collagen-tailed quaternary structural forms of acetylcholinesterase.