Streptomyces K15 DD-peptidase-catalysed reactions with suicide beta-lactam carbonyl donors.

The values of the kinetic parameters that govern the interactions between the Streptomyces K15 DD-peptidase and beta-lactam compounds were determined by measuring the inactivating effect that these compounds exert on the transpeptidase activity of the enzyme and, in the case of [14C]benzylpenicillin and [14C]cefoxitin, by measuring the amounts of acyl-enzyme formed during the reaction. K15 DD-peptidase binds benzylpenicillin or cefoxitin at a molar ratio of 1:1. Benzylpenicilloate is the major product released during breakdown of the acyl-enzyme formed with benzylpenicillin. Benzylpenicillin is not a better acylating agent than the amide Ac2-L-Lys-D-Ala-D-Ala and ester Ac2-L-Lys-D-Ala-D-lactatecarbonyl-donor substrates. beta-Lactam compounds possessing a methoxy group on the alpha-face of the molecule show high inactivating potency.     

Callus formation and induction of a cell suspension culture from Acacia senegal

Cell proliferation has been induced from the cambial zone of a branch of Acacia senegal, kept on the basal Knop and Ball medium in the presence of auxin. Transferred on the more complete nutrient medium of Schenk and Hildebrandt, the colonies gave rise to several cell lines. One of the friable lines, consisting of aggregates of parenchymatous cells, gave a cell suspension culture in an agitated liquid medium which is maintained as a strain of illimited growth. The heterogeneous suspension did not undergo noticeable changes after eight transfers. Aggregates collected on a 1000-m nylon seive were able to grow on a solid medium and gave back a friable callus similar to the initial colonies.     

Induction of heavy metal binding groups by dexamethasone and Zn in cultured Chinese hamster ovary cells

Cd binding capacity and pulse polarography were used to study the inducibility of sulfhydryl groups in cultured Chinese hamster ovary cells (wild type and a Cd-resistant mutant) in response to dexamethasone (dex) and Zn. Evidence is presented that both the wild type and the mutant responded to dex and Zn treatment by induction of sulfhydryl groups. In wild type for Zn and dex as well as in the mutant for dex, this induction seems to be in the form of sulfhydryls attached to particulate or membrane fractions in the cells. For Zn in the Cd-resistant mutant the induction was in the form of metallothionein.     

Analysis of two chloride requirements for sodium-dependent amino acid and glucose transport by intestinal brush-border membrane vesicles of fish

Intestinal brush border vesicles of a Mediterranean sea fish (Dicentrarchus labrax) were prepared using the Ca²⁺-sedimentation method. The transport of glucose, glycine and 2-aminoisobutyric acid is energized by an Na⁺ gradient ($\text{out > in}$). In addition, amino acid uptake requires Cl^? in the extravesicular medium (2-aminoisobutyric acid more than glycine). This Na⁺- and Cl^?-dependent uptake is electrogenic, since it can be stimulated by negative charges inside the vesicles. The specific Cl^? requirement of glycine and 2-aminoisobutyric acid transport is markedly influenced by pH, a change from 6.5 to 8.4 reducing the role played by Cl^?. In the presence of Cl^?, the $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ of 2-aminoisobutyric acid uptake is reduced and its $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ is enhanced. Cl^? affects also a non-saturable Na⁺-dependent component of this amino acid uptake. Amino acid transport is also increased by intravesicular Cl^? (2-aminoisobutyric acid less than glycine). This effect is more concerned with glucose uptake, which can be then multiplied by 2.3. A concentration gradient ($\text{in > out}$) as well as the presence of Na⁺ in the incubation medium seems to enter into this requirement. This intravesicular Cl^? effect is not influenced by pH between 6.5 and 8.4.     

Teleonomical optimization of a fractal model of the pulmonary arterial bed

Modeling the pulmonary arterial tree (PAT) is considered here as an optimal synthesis problem. Firstly, a class of candidate models is specified: the three-dimensional symmetric dichotomous fractal trees of elastic tubes described by Womersley's equations. Secondly, the parameters are shown to be constrained by interactions of PAT with the rest of the body; these constraints are used to limit the volume of the parametric space to which attention will be directed in the synthesis step. Thirdly, a teleonomical hypothesis is proposed: a naturally selected PAT must have a minimal input impedance under conditions keeping total arterial volume and distensibility as small as possible. This hypothesis is translated in mathematical terms and the resulting cost-function minimized in the limited parametric volume. The optimal model has parameter values and an impedance spectrum corresponding satisfactorily with real data. Moreover this model gives a clear picture of the internal hemodynamic behavior of PAT as an impedance matching device.     

Production and purification of monoclonal antibodies to Pisum and Avena phytochrome

At least nine monoclonal antibodies against phytochrome from Pisum sativum L. and 20 against phytochrome from Avena sativa L. have been obtained from mouse hybridomas that were produced by fusion of spleen cells with SP 2/O-Ag14 myeloma cells. Hybridomas were selected and cloned in a single step by plating on a semisolid methylcellulose medium. Eight antibodies to Pisum and one to Avena phytochrome were immunopurified from hybridoma medium or ascitic fluid. When necessary, secreted antibodies were verified to be against phytochrome by demonstrating to be against phytochrome by demonstrating immunoadsorption of phytochrome, detected as loss of photoactivity and-or by appearance of the approx. 120,000-dalton phytochrome band upon sodium dodecyl sulfate polyacrylamide gel electrophoresis.     

Distribution of corticotropin-releasing factor in ovine brain determined by radioimmunoassay

We have developed and used a sensitive and specific radioimmunoassay to demonstrate the presence of CRF-like immunoreactivity in extra-hypothalamic areas of ovine brain. Synthetic CRF displaced antibody bound tracer at an ED50 value of 200 pg and there was no cross-reactivity with LHRH, TRH, ACTH, beta-endorphin and several other peptides. Displacement of bound 125I-CRF by brain extracts exhibited curves parallel to synthetic CRF standards. Highest concentrations (1 ng/mg tissue) of CRF-like immunoreactivity were found in the median eminence but surprisingly, high concentrations of CRF-like immunoreactivity were found in frontal, parietal, occipital and particularly temporal areas of cerebral cortex. Much lower concentrations were found in other brain areas including the basal ganglia, limbic system and brain stem.     

DNA and histone H1 interact with different domains of HMG 1 and 2 proteins.

High mobility group (HMG) proteins 1 and 2 from calf thymus have been digested under structuring conditions (0.35 M NaCl, pH 7.1) with two proteases of different specificities, trypsin and V8. The two proteases give a different but restricted pattern of peptides in a time course digestion study. However, when the interactions of the peptides with DNA are studied by blotting, a closely related peptide from HMG-1 and -2 does not show any apparent binding. This peptide, from the V8 protease digestion, has been isolated by DNA-cellulose chromatography and has the amino acid composition predicted for a fragment containing the two C-terminal domains of the protein, i.e., approximately residues 74-243 for HMG-1. The same peptide shows the only interaction detectable with labelled histone H1. A separate function for the different domains of HMG proteins 1 and 2 is proposed.