Ion Homeostasis in Chloroplasts under Salinity and Mineral Deficiency: II. Solute Distribution between Chloroplasts and Extrachloroplastic Space under Excess or Deficiency of Sulfate, Phosphate, or Magnesium

Spinach (Spinacia oleracea var “Yates”) plants grown hydroponically were exposed to an excess or deficiency of various mineral ions. Solutes were measured in leaf extracts and in isolated intact chloroplasts. Under phosphate (120 millimoles per liter NaH₂ PO₄), sulfate (200 millimolar per liter (Na₂ SO₄), or magnesium excess (150 millimolar per liter MgCl₂), concentrations of these ions in leaf extracts increased, but in chloroplasts, concentrations of all ions remained constant. Concentrations of quarternary ammonium compounds in chloroplasts increased. Under mild phosphate or magnesium deficiency, concentrations of these ions decreased in chloroplasts less than in whole leaf extracts. Under severe sulfate deficiency causing chlorosis in younger leaves, sulfate concentrations in chloroplasts remained even unchanged, despite a drastic decrease of sulfate concentrations both in green and in chlorotic leaves. Together with results from a companion study (G Schröppel-Meier, WM Kaiser 1988 Plant Physiol 87: 822-827) our data demonstrate that leaf cells are able to keep the concentrations of several mineral ions rather constant in metabolically active compartments even at extremely large variations of ion concentrations in the culture solution and in the leaves.     

A minority of 46,XX true hermaphrodites are positive for the Y-DNA sequence including SRY

Summary A total of 30 cases of 46,XX true hermaphroditism was analysed for Y-DNA sequences including the recently cloned gene for male testis-determination SRY. In 3 cases, a portion of the Y chromosome including SRY was present and, in 2 cases, was localised, to Xp22 by in situ hybridisation. Since previous studies have shown that the majority of XX males are generated by an X-Y chromosomal interchange, the Xp22 position of the Yp material suggests that certain cases of hermaphroditism can arise by the same meiotic event. The phenotype in the 3 SRY-positive cases may be caused by X-inactivation resulting in somatic mosaicism of testis-determining factor expression giving rise to both testicular and ovarian tissues. Autosomal or X-linked mutation(s) elsewhere in the sex-determining pathway may explain the phenotype observed in the remaining 27 SRY-negative cases.     

haemolysin of Escherichia coli: Comparison of pore-forming properties between chromosome and plasmid-encoded haemolysins

Abstract Lipid bilayer experiments were performed with chromosome-encoded haemolysin of Escherichia coli . The addition of the toxin to the aqueous phase bathing lipid bilayer membranes of asolectin resulted in the formation of transient ion-permeable channels with two states at small transmembrane voltages. One is prestate (single-channel conductance 40 pS in 0.15 M KCl) of the open state, which had a single-channel conductance of 420 pS in 0.15 M KCl and a mean lifetime of 30 s. Membranes formed of pure lipids were rather inactive targets for this haemolysin. Experiments with different salts suggested that the haemolysin channel was highly cation-selective at neutral pH. The mobility sequence of the cations in the channel was similar if not identical to their mobility sequence in the aqueous phase. The single-channel data were consistent with a wide, water-filled channel with an estimated minimal diameter of about 1 nm. The pore-forming properties of chromosome-encoded haemolysin were compared with those of plasmid-encoded haemolysin. Both toxins share common features, oligomerize probably to form pores in lipid bilayer membranes. Both types of haemolysin channels have similar properties but different lifetimes.     

Monoclonal antipeptide antibodies to the glucocorticoid receptor.

The generation of monoclonal antibodies to synthetic peptides of the glucocorticoid receptor is described. Two antibodies to sequences from the DNA binding region are IgMs. Two other antibodies to sequences in the steroid binding region and the C-terminus belong to the IgG class. The specificity of the IgG binding to the receptor in an ELISA assay is demonstrated by competition with the relevant peptides. Both IgGs are able to recognize the receptor in Western blots, but do not form stable complexes in sucrose gradients. Steroid binding to the receptor is not influenced by preincubation with antibodies. This indicates that denaturation or distortion of the receptor is necessary for the accessibility of these antibodies to their epitopes. Both antibodies can be used to stain the glucocorticoid receptor in neoplastic cells of patients suffering from chronic lymphatic leukemia.     

Cytogenetic and molecular characterization of a newly established neuroblastoma cell line LS

Summary A new human neuroblastoma cell line (LS) that originated from an abdominal tumor of a 16-month-old girl is presented; it was classified, according to Evans, as being stage III. Morphological (dense-core particles) and biochemical characteristics (dopamine--hydroxylase, acetylcholinesterase, neuron-specific-enolase) confirmed the diagnosis. In addition to a slightly variable modal chromosome number of 48 or 49 (because of marker-chromosomes and autosomal trisomies), cytogenetic analysis revealed two constantly appearing chromosomes with homogeneously stained regions (HSR's). The karyo-type remained constant over 50 passages in vitro [49,XX, –12,+der5, + 17,+mar1,+mar2]. Double minutes were a rare phenomenon and appeared only in a few metaphases. In situ hybridization showed that some of the HSR's consisted of amplified N-myc copies. The distribution of the N-myc copies according to in situ hybridization signals along the HSR's was compared with the data of Southern and Northern blotting analyses.     

Effect of monensin on receptor recycling during continuous endocytosis of asialoorosomucoid

The binding of asialoglycoproteins to their liver cell receptor results in internalization of the ligand-receptor complex. These complexes rapidly appear in intracellular compartments termed endosomes whose acidification results in ligand-receptor dissociation. Ligand and receptor subsequently segregate: ligand is transported to lysosomes and is degraded while receptor recycles to the cell surface. The proton ionophore monensin prevents acidification of endosomes and reversibly inhibits this acid-dependent dissociation of ligand from receptor. The present study determined the effect of monensin treatment of short-term cultured rat hepatocytes on cell-surface-receptor content, determined both by their binding activity and immunologically, following continuous endocytosis of asialoorosomucoid. Inclusion of 5 microM monensin in the incubation medium reduced the number of immunologically detectable cell-surface receptors by 20% in the absence of ligand. During continuous endocytosis of asialoorosomucoid, inclusion of monensin resulted in a 30-40% reduction of cell-surface receptor detectable either by ligand binding or immunologically. These results suggest that the reduced liver-cell-surface content of receptor in monensin is due to intracellular trapping of ligand-receptor complexes. The reduction of surface receptor during monensin incubation in the absence of ligand suggests that "constitutive recycling" of plasma membrane components also requires intracellular acidification.     

Mitochondrial aldehyde dehydrogenase from human liver. Primary structure, differences in relation to the cytosolic enzyme, and functional correlations

The 500-residue amino acid sequence of the subunit of mitochondrial human liver aldehyde dehydrogenase is reported. It is the first structure determined for this enzyme type from any species, and is based on peptides from treatments with trypsin, CNBr, staphylococcal Glu-specific protease, and hydroxylamine. The chain is not blocked (in contrast to that of the acetylated cytosolic enzyme form), but shows N-terminal processing heterogeneity over the first seven positions. Otherwise, no evidence for subunit microheterogeneities was obtained. The structure displays 68% positional identity with that of the corresponding cytosolic enzyme, and comparisons allow functional interpretations for several segments. A region with segments suggested to participate in coenzyme binding is the most highly conserved long segment of the entire structure (positions 194-274). Cys-302, identified in the cytosolic enzyme in relation to the disulfiram reaction, is also present in the mitochondrial enzyme. A new model of the active site appears possible and involves a hydrophobic cleft. Near-total lack of conservation of the N-terminal segments may reflect a role of the N-terminal region in signaling the transport of the mitochondrial protein chains. Non-conservation of interior regions may reflect the differences between the two enzyme forms in subunit interactions, explaining the lack of heterotetrameric molecules. The presence of some internal repeat structures is also noted as well as apparently general features of differences between cytosolic and mitochondrial enzymes.     

Der Sperlingskauz (Glaucidium passerinum) im Schwarzwald

Summary After a decrease and extinction due to deforestation the population has been reestablished by releasing captive-bred owls. Now about 40 territories are occupied with an average density of 0,8–1,0 territories/10 km². Highest density: 17 territories/80 km².     

Efficacy of high-frequency ventilation in presence of extensive ventilation-perfusion mismatch

Ten anesthetized normal dogs were each given two methacholine inhalational challenges to produce large amounts of low ventilation-perfusion (VA/Q) regions but little shunt. After one challenge, high-frequency ventilation (HFV) was applied, whereas after the other conventional mechanical ventilation (MV) was used, the order being randomized. Levels of both ventilatory modes were selected prior to challenge so as to result in similar and normal mean airway pressures and arterial PCO2 levels during control conditions. Gas exchange was assessed by both respiratory and multiple inert-gas transfer. Comparing the effect of HFV and MV, no statistically significant differences were found for lung resistance, pulmonary hemodynamic indices, arterial and mixed venous PO2, expired-arterial PO2 differences, or inert-gas data expressed as retention-excretion differences. The only variables that were different were mean airway pressure (2 cm higher during HFV, P less than 0.04) and arterial PCO2 (10 Torr higher during HFV, P less than 0.002). These results suggest that in this canine model of lung disease characterized by large amounts of low VA/Q regions, HFV is no more effective in delivering fresh gas to such regions than is MV.     

Heterogeneity of glucagon receptors of rat hepatocytes: a synthetic peptide probe for the high affinity site

A glucagon analog with the following sequence has been synthesized: His- Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg -Leu-Gln-Glu-Phe-Leu-Gln-Trp-Ala-Leu-Gln-Thr. When interacting with rat hepatocytes, the analog mimics, in part, the activities of glucagon in receptor binding and inhibition of carbohydrate incorporation into glycogen. Comparison of the binding of the analog with that of glucagon demonstrates the existence of two distinct homogeneous populations of glucagon receptors. The synthetic analog acts as a specific probe for those receptors that have a high affinity for glucagon.