Antigenic determinants of the membrane-bound hydrogenase in Alcaligenes eutrophus are exposed toward the periplasm.

Electron microscopic immunogold labeling experiments were performed with ultrathin sections of plasmolyzed cells of Alcaligenes eutrophus and "whole-mount" samples of spheroplasts and protoplasts. They demonstrated that antigenic determinants of the membrane-bound hydrogenase are exposed, at the outside of the cytoplasmic membrane, to the periplasm.     

Biosynthesis and action of nitric oxide in mammalian cells

Nitric oxide (NO) can act as a vasorelaxant, a modulator of neurotransmission and a defence against pathogens. However, under certain conditions, NO can also have damaging effects to cells. Whether NO is useful or harmful depends on its chemical fate, and on the rate and location of its production. Here, we discuss progress in NO chemistry and the enzymology of NO synthases, and we will also attempt to explai its actions in the cardiovascular, nervous and immune systems.     

Genetic variability of plant characters in the partial inbreeder Collinsia heterophylla (Scrophulariaceae)

Quantitative genetic variability for six characters was estimated in four populations of the annual plant, Collinsia heterophylla, with estimated selling rates ranging from 0.36 to 0.68. Based on large samples of parental plants, all four populations showed significant genetic variation for two or more characters, and there was no sign that the more selfing populations had lower amounts of genetic variance or lower heritability values. Autogamous fruit set rates in the absence of pollinators also showed significant heritability in one population.     

Chemical characterization of two lipopolysaccharide species isolated from Rhizobium loti NZP2213

Phenol-water extraction of Rhizobium loti NZP2213 cells allowed a simultaneous isolation of two structurally different lipopolysaccharides, from the aqueous (LPS-W) and phenol (LPS-P) phase that differed in their sodium doexycholate-PAGE pattern and composition. LPS-W showed a profile indicating an R-type LPS; LPS-P had a cluster of poorly resolved bands in the high-molecular-weight region. LPS-P contained large amounts of 6-deoxy-l-talose (6dTal), and a small amount of 2-O-methyl-6-deoxy-talose (molar ratio 30:1), both of which were completely absent in LPS-W. Methylation analysis gave only one major product, 2,4-di-O-methyl-6dTal, indicating that the O-chain is composed of a homopolymer of 1,3-linked 6dTal, having the methylated 6dTal (2-O-me-6dTal) probably localized at the non-reducing end of the O-chain. This homopolymeric O-chain was additionally O-acetylated, as evidenced by GC-MS and by ¹³C NMR analysis. The lipid A moieties of both LPS-W and LPS-P showed almost identical composition, with six, different 3-OH fatty acids and with two, so far not described, long-chain 4-oxo-fatty acids, all being amide-linked, and with 27-OH-28:0 as the main ester-linked fatty acid. Lipid A was of the lipid A_DAG-type, i.e., having a (phosphorylated) 2,3-diamino-2,3-dideoxy-d-glucose-containing lipid A backbone. Lipid A_DAG is widespread among species of the -2 group of Proteobacteria, but has so far not been encountered in any other rhizobial or agrobacterial species.     

Quaternary structure of the hydroxylamine oxidoreductase from Nitrosomonas europaea

The hydroxylamine oxidoreductase from Nitrosomonas europaea was prepared to apparent electrophoretic homogeneity. Electron microscopy of negatively stained preparations of the sample revealed an overall diameter of about 8.8 nm of the enzyme particle. The native structure was determined as a tetrahedron-like assembly of identical subunits exhibiting four protein masses.Abbreviations ESI Electron spectroscopic imaging - HAO Hydroxylamine oxidoreductase     

Structure of the murine Ia-associated invariant (Ii) chain as deduced from a cDNA clone

The invariant (Ii) chain is a membrane-spanning glycoprotein found intracellularly associated with class II major histocompatibility complex (MHC) molecules. Using hybrid-selected translation and the Ii-specific monoclonal antibody In-1, we have isolated a cDNA clone (pIi-5) coding for most of the Ii chain. Sequence analysis of this clone reveals an open reading frame encoding 169 amino acid residues. The protein is rich in methionine and contains two potential N-glycosylation sites. No stretch of uncharged amino acid residues, characteristic for a membrane-spanning segment, is found close to the COOH-terminal end. There is one, however, close to the NH2-terminal end. As it is know that approximately 20 amino acid residues of Ii chain are exposed on the cytoplasmic side, we conclude that the Ii chain spans the membrane exposing the NH2 terminus on the cytoplasmic side and the COOH terminus on the luminal side.     

Pyruvate carboxylase from Aspergillus nidulans. Effects of regulatory modifiers on the structure of the enzyme

Pigment-binding protein of the facultatively phototrophic bacterium Rhodospeudomonas capsulata could be selectively synthesized in toluene-treated cells as well as in homologous and heterologous cell-free translation systems by isolated polysomes. It is shown that the pigment-binding polypeptides of the light-harvesting complexes are encoded by messenger RNA of extreme longevity. The dependence of their synthesis on the concomitant synthesis of tetrapyrroles was demonstrated in the toluene-treated cells. The large Mr-28 000 polypeptide of the reaction center and the Mr-10 000 pigment-binding polypeptide of the light-harvesting complex II were found to be synthesized by free (water-soluble) polysomes without a cleavable 'leader' or 'signal' peptide [reviewed by W. Wickner (1979) Annu. Rev. Biochem. 48, 23-45]. The Mr-10 000 polypeptide, as synthesized in vitro, was studied in more detail. Unlike the membrane-assembled polypeptide in vivo it was insoluble in an organic solvent mixture (chloroform/methanol 1:1, v/v). After detergent denaturation in the presence of membrane isolated from the organism it became organic-solvent-soluble. Obviously the polypeptide could be induced to assume alternative conformations in which its apolar residues were either exposed to the solvent or buried within. These findings, in agreement with Wickner's hypothesis, indicate that the Mr-10 000 polypeptide may enter the lipid bilayer by a 'membrane-triggered' conformational change.     

Electron microscopic studies on liver 5-aminolaevulinate synthase

The structure of chick embryo liver 5-aminolaevulinate synthase has been examined by electron microscopic studies using negative staining. From the different projections of the enzyme particles observed in electron micrographs, a model for the enzyme molecule has been proposed. In this model, an enzyme molecule consists of two curved and identical subunits associated in opposite polarities. From the dimensions of an enzyme molecule subunit measured from electron micrographs, the relative molecular mass of each subunit is estimated to be 70 000.     

Biological activity assessment of the 26,23-lactones of 1,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3 and their binding properties to chick intestinal receptor and plasma vitamin D binding protein

The binding of the natural and unnatural diastereoisomers 25-hydroxyvitamin D3-26,23-lactone and 1,25 dihydroxyvitamin D3-26,23-lactone to the vitamin D-binding protein (DBP) and 1,25 dihydroxyvitamin D3 [1,25(OH)2D3] chick intestinal receptor have been investigated. Also, the biological activities, under in vivo conditions, of these compounds, in terms of intestinal calcium absorption (ICA) and bone calcium mobilization (BCM), in the chick are reported. The presence of the lactone ring in the C23-C26 position of the seco-steroid side chain increased two to three times the ability of both 25(OH)D3 and 1,25(OH)2D3 to displace 25(OH)[3H]D3 from the D-binding protein; however, the DBP could not distinguish between the various diastereoisomers. In contrast, the unnatural form (23R,25S) of the 25-hydroxy-lactone was found to be 10-fold more potent than the natural form, and the unnatural (23R,25S)1,25(OH)2D3-26,23-lactone three times more potent than the natural 1,25-dihydroxy-lactone in displacing 1,25(OH)2[3H]D3 from its intestinal receptor. While studying the biological activity of these lactone compounds, it was found that the natural form of the 25-hydroxy-lactone increased the intestinal calcium absorption 48 h after injection (16.25 nmol), while bone calcium mobilization was decreased by the same dose of the 25-hydroxy-lactone. The 1,25-dihydroxyvitamin D3-26,23-lactone in both its natural and unnatural forms was found to be active in stimulating ICA and BCM. These results suggest that the 25-hydroxy-lactone has some biological activity in the chick and that 1,25(OH)2D3-26,23-lactone can mediate ICA and BCM biological responses, probably through an interaction with 1,25-(OH)2D3 specific receptors in these target tissues.     

Comments on “Seed germination as a thermobiological problem”

Summary In the above mentioned article [1] the notion of a time-dependent Gibbs free energy has been introduced to explain the observed time-pattern of embryo growth in seeds. Furthermore, the notion of a non-random thermal communication has been inferred from an inspection of the shapes of germination time distributions. It can be shown, however, that the reasoning leading to the time-dependent thermodynamic potential is based on inappropriate interpretation of kinetic equations, and that the shape of the distributions of germination time might be a natural consequence of the initial distribution of embryo size in the seeds.Discussion about the Paper Seed Germination as a Thermobiological Problem by L. G. Labouriau Radiation and Environmental Biophysics 15:345–366 (1978)