Genera of Scrophulariaceae in the páramos of the Venezuelan Andes

A report on the family Scrophulariaceae in the páramos of the Venezuelan Andes is made, which includes 13 genera. A key to the genera is provided.     

Effects of in vivo monoclonal anti-I-A antibody treatment in neonatal mice on intrathymic and peripheral class II antigen expression

Intrathymic, Ia-bearing antigen-presenting cells (APC) are believed to play an important role in the development of a mature, functional T-cell repertoire. We used chronic in vivo treatment of neonatal mice with anti-I-A monoclonal Ab (MAb) to examine the expression of I-A and I-E antigens on intrathymic and peripheral APC. Three weeks after continuous treatment with anti-I-A MAb, FACS analysis of unfractionated spleen cells revealed a 75-90% reduction in the number of I-A bearing cells. Splenic antigen-presenting capacity measured by the ability of unseparated or density gradient-enriched APC to stimulate I-A- or I-E-reactive T-cell hybridomas was also greatly reduced. In contrast to the expression of I-A and I-E molecules in the splenic APC, anti-I-A MAb treatment resulted in decreased thymic APC I-A expression without significant changes in I-E as measured by FACS analysis. This was confirmed in functional studies in which allo-I-A- or auto-I-A-reactive T-cell hybridomas could not be stimulated by treated thymic APC. Unlike splenic APC, anti-I-A-treated thymic APC did not differ significantly from normals in their ability to stimulate allo-I-E-reactive T hybridomas. This lack of linkage or comodulation of I-A and I-E expression on thymic but not splenic APC may allow us to study the role of I-A molecules and I-E molecules on the development and expansion of functional, mature T-cell repertoires.     

Gene activity of polytene chromosomes in Drosophila species of the obscura group

The polytene chromosome puffing patterns of Drosophila guanche were established and compared with those of Drosophila subobscura. A total of 150 loci, active in some of the 17 developmental stages studied, were described and 23 of them were found to form the characteristic puffing pattern of D. guanche. Taking into account the number of puffs as well as the gene activity of each chromosome and the total gene activity, D. guanche seems to be less active than D. subobscura. Although both species show a degree of homology in their puffing patterns lower than that found for sibling species, the degree of homology is stronger than that between species belonging to the same group but to different subgroups. Thus, D. guanche and D. subobscura must be considered as phylogenetically closely related species, belonging to the same subgroup.     

Function of neutral endopeptidase on the cell membrane of human neutrophils

Intact human neutrophils hydrolyzed N-formyl-Met-Leu-[3H]Phe (fMLP) and released Leu-[3H]Phe, cleaving 45-50% of the peptide within 20 min at 37 degrees C. The dipeptide after its release was then hydrolyzed to free amino acids by a dipeptidase (EC 3.4.13.11). This activity, present in plasma membrane-enriched fractions of neutrophil lysates, was also inhibited over 90% by phosphoramidon, an inhibitor of neutral endopeptidase (NEP, EC 3.4.24.11). Dithiothreitol and EDTA inhibited the activity to a comparable degree, suggesting the requirement for a heavy metal cofactor. Bestatin and amastatin, inhibitors of aminopeptidases (but not human kidney NEP), did not inhibit the rate of fMLP degradation but prevented the production of free phenylalanine and enhanced the accumulation of Leu-Phe. Of other inhibitors, alpha 1-antitrypsin and alpha 2-macroglobulin slightly enhanced the rate of fMLP hydrolysis by neutrophils, and others tested were ineffective. Rabbit antiserum to homogeneous human kidney NEP reacted specifically with a 100-kDa protein present in sodium dodecyl sulfate-solubilized neutrophils. The Mr of this protein was slightly larger than that of the kidney enzyme in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The antiserum incubated with intact cells specifically inhibited the degradation of fMLP over 70%. First, we confirm that NEP present on the plasma membrane cleaves fMLP at the Met-Leu bond; then the dipeptide Leu-Phe is cleaved by a dipeptidase. Finally, inhibition of NEP completely blocks fMLP-mediated chemotaxis. Thus, the enzyme may play an important role in modulating chemotactic responses.     

Leiurus quinquestriatus venom inhibits different kinds of Ca2+-dependent K+ channels

A minor protein component of Leiurus quinquestriatus venom has been reported to inhibit selectively the apamin-insensitive Ca2+-dependent K+ channels of mammalian skeletal muscle (Miller, C., Moczydlowski, E., Latorre, R. and Phillips, M. (1985) Nature 313, 316-318). We report the effect of the venom on both the apamin-insensitive channels of the human erythrocyte, the Ehrlich cell and the rat thymocyte and the apamin-sensitive channel of the guinea pig hepatocyte. The venom inhibited Ca2+-dependent K+ transport in all the cases with a Ki value within the range of 1 to 10 micrograms/ml, similar to that reported previously in muscle. Valinomycin-induced K+ transport was also antagonized by the venom but its sensitivity was about 1/10 as much as that of the Ca2+-dependent K+ channel.     

Effect of decreased ferrochelatase activity on iron and porphyrin content in mitochondria of mice with porphyria induced by griseofulvin

The content of iron and protoporphyrin in liver mitochondria from mice with porphyria induced by griseofulvin was measured. The amount of porphyrin was 0.0076 +/- 0.0043, 4.11 +/- 0.58 and 22.2 +/- 6.8 nmol/mg protein (n = 5) in mitochondria from control animals and animals treated with griseofulvin for 3 days and 4-5 weeks, respectively. The energy coupling of the mitochondria was greatly diminished after 4-5 weeks of treatment, and the ferrochelatase activity was inhibited 80-90%, compared to that of control animals. Mitochondrial preparations isolated by differential centrifugation were contaminated with iron-containing lysosomes which could be removed by Percoll density-gradient centrifugation. In purified mitochondrial preparations no change in the amount of non-heme iron was found after griseofulvin feeding, representing 3.36 +/- 0.15, 3.97 +/- 0.40 and 3.59 +/- 0.23 nmol/mg protein for control animals, 3 days- and 4-5 weeks-treated animals, respectively (n = 4). A mitochondrial iron pool previously identified in rat liver mitochondria and shown to be available for heme synthesis in vitro (Tanger?s, A. (1985) Biochim. Biophys. Acta 843, 199-207) was also present in mitochondria from mice. The magnitude of this iron pool, as well as its availability for heme synthesis, was not changed after treatment of the animals with griseofulvin. The fact that porphyrin, but not iron, accumulated in the mitochondria when ferrochelatase was inhibited is discussed with regard to our understanding of the process of heme synthesis and its regulation.     

Quantitation and characterization of tau factor in porcine tissues

Using a monospecific antibody against brain tau factor purified by affinity chromatography, we have studied the distribution of tau factor or related polypeptides in different cells. The presence of tau in all cell types tested was demonstrated by a radioimmunoassay. Tau factor-related proteins were found in liver, spleen, pancreas, kidney and lung, although at much lower levels than that found in neural cells. In all cases, they copolymerized with tubulin and were heat-resistant. When the distribution of tau factor-related proteins was studied by Western blotting, tau factor antiserum reacted against peptides with an electrophoretic mobility that was similar to those of brain tau factor peptides. Immunofluorescence studies have also been performed with the same antibody to determine the distribution of tau factor-related peptides in PK15 cells. Our results indicated that these peptides were associated to the microtubule network.     

The effect of pH on the phase transition temperature of dipalmitoylphosphatidylcholine-palmitic acid liposomes

The shift in the gel-liquid crystal phase transition temperature (tm) of dipalmitoylphosphatidylcholine liposomes induced by incorporation of 10 mol% palmitic acid, was measured by 90 degrees light scattering at different bulk pH values. It has been found that the tm shift decreases sigmoidally from 4.7 to -0.3 degrees C as the bulk pH is raised from 5 to 11. Since it is in this range that the carboxyl group of a membrane-bound fatty acid should ionize, our results can be interpreted to mean that there is relationship between the tm shift and the degree of dissociation of palmitic acid, the uncharged fatty acid increasing tm and its conjugate, anionic form, slightly decreasing the transition temperature of dipalmitoylphosphatidylcholine liposomes. The experimental results are fitted by a modified form of the Henderson-Hasselbach equilibrium expression which takes into account the effect of the anionic fatty acid on the surface potential and hence, on the surface pH of liposomes, according to Gouy-Chapman and Boltzmann equations, respectively. Best fit between theory and experiments is found when the intrinsic interfacial pK of palmitic acid is set equal to 7.7. This high pK value can be explained as due to the effect of the lower dielectric constant of the interfacial region, as compared to bulk water, on the acid-base dissociation of the carboxyl group. The results presented here show that upon incorporation of palmitic acid, the phase transition of dipalmitoylphosphatidylcholine bilayers becomes extremely sensitive to changes of pH in the vicinity of the physiological range. This property is not shown by the pure phospholipid bilayers in the same pH range.     

Stimulation of gibberellin activity in winter wheat by metribuzin

Sublethal doses of metribuzin applied to wheat plants at the stage of ear emergence increased endogenous gibberellin levels in the ears. The activation of hormonal systems in connection with “chemical stress” is briefly discussed.