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LaxWO3 - Perovskite: A New Sensor Material for the Potentiometric Detection of Dissolved Oxygen
No full textThe suitability of the La,WO3 -perovskites as electrode materials for potentiometric measurements
of dissolved oxygen at room temperature or below is demonstrated by EMF data of a Lag 2WO3
ceramics. A model of potential formation is presented which explains the observed dependency of the
EMF on the concentration of dissolved oxygen as well as on the solution acidity and on [WO,42-]
TAXONOMICALLY USEFUL TEST PROCEDURES PERTAINING TO BACTERIAL LIPOQUINONES AND ASSOCIATED FUNCTIONS, WITH SPECIAL REFERENCE TO FLAVOBACTERIUM AND CYTOPHAGA
No full textThe following phenomena related to the respiratory quinones of chemo-organotrophic
bacteria are considered regarding their use by the microbiologist: (i) Types and concentrations
of quinones present in the cells, (ii) reaction sites of quinones in the
respiring membrane, (iii) changes in quinone contents with culture conditions, (iv)
effect of fumarate on oxygen-limited growth, (v) electron transport rates in membrane
particles with varied donors and acceptors, and (vi) quinone isoprenologs, and degree
of unsaturation and branching of the terpenoid side chains. The taxonomic and diagnostic
significance of such information is discussed for selected organisms, among
them, collection strains representing some Flavobacterium and Cytophaga species
SOME ECOLOGICAL ASPECTS OF AQUATIC CYTOPHAGAS
No full textCytophaga-like bacteria are at least temporarily abundant in almost all aquatic
habitats, although the techniques which are currently available for large scale identification
and enumeration, may only lead to rather vague taxonomic conclusions. As
for obtaining maximal plate counts, the enumeration of relatively fastidious and
mostly organic nitrogen-requiring marine forms could be considerably improved by
using 38 mg/l of polymyxin B as a counterselective agent.
From a collection of chitin-degrading and predominantly estuarine bacteria, Cytophagaceae=
strains were selected to study utilization of glucose ‚production of depolymerizing
enzymes and survival under hydrostatic pressure. While swarming (spreading)
as one of the most striking colony features was insufficient as taxonomic indicator,
Cytophaga-like isolates could be classified on the basis of their substrate
requirements for swarming. Different swarming types could at least partly be ranked
according to their kinetic parametere for glucose utilization. While being able to
degrade various biopolymers effectively even at low water temperatures, psychrotrophic,
oligonitrophilic isolates suggest a key position for this type of freshwater
cytophagas in major biogeochemical pathways of the carbon cycle. Growth rates,production
of chitin-degrading enzymes as well as autolytic activities of one of these
isolates (Cytophaga johnsonae, strain C 21) were characterized by similar temperature
responses. In contrast to deep freshwater habitats, nothing is known about a corresponding
contribution of marine Cytophaga spp. to biodegradation processes in the
deep sea. It could be shown,however, that even a starved culture of an estuarine
surface water isolate was able to survive hydrostatic pressures up to 500 at
SYNTHESIS OF 5-AZACYTOSINE 2’-DEOXYRIBONUCLEOSIDES, PROPERTIES AND BIOLOGICAL ACTIVITY
No full textThe effect of the o-D anomer Ia on L 1210 mouse leukemia cells was
studied. This nucleoside inhibited the cell growth in vitro (IC55 about
Lx 10-°m), and was also active in vivo in increasing the life span of
mice with L1210 leukemia (800 to 1000 mg/kg) by 100%. It is Supposed that
the action of the o-D anomer Ia is due to its conversion to Ib shown by
HPCL performed on water solutions of both anomers. Similarly, the conversion
of Ib to Ia was observed. Hydrolysis of 2'-deoxy-5-azacytidine (Ib)
or its «-D anomer Ia with aqueous ammonia affords N-amidino-N’-(2-deoxyß-
D-erythropentofuranosyl)urea formate (IVb). Cyclocondensation Of this
compound with dimethylformamide dimethyl acetal leads to a mixture of
anomeric nucleosides Ia and Ib. Stannic chloride catalysed condensation of
blocked 2-deoxy-D-ribopyranose with silylated 5-azacytosine and subsequent
methanolysis of the protected intermediates affords anomeric deoxyribopyranosyl
nucleoside Va and vb which do not exhibit biological extivity.
A series of 6-substituted deoxy nucleosides was prepared by direct glycosylation
and the isocyanate procedure. 6-Amino-2’-deoxy-5-azacytidine
prevents the growth of E. coli; the inhibition is completely reversed by
natural purine bases and/or nucleosides
INHIBITORS OF OLIGOSACCHARIDE PROCESSING
No full textMost proteins present on the surface of eukaryotic cells and proteins secreted
by them are glycoproteins. Glycoproteins, generally speaking, may contain asparagine-
-linked (N-linked) or serine/threonine linked (0-linked) oligosaccharides. A given
protein may contain either one or both types of oligosaccharides. Notwithstanding
their common occurrence -glycoproteins are found in bacteria, yeasts and all higher
eukaryotes- there is no consensus on the function of protein bound glycans. They are
thought to be involved in protection against proteolysis and contribute to or modify
the folding of the polypeptide backbone. Protein bound glycans are also thought to
constitute signals for intracellular traffic of glycoproteins, and may participate in
determining the specificity of interactions between receptors and ligands and the
interactions between cells.
In present-day biotechnology, the importance of protein bound carbohydrate is
likely to come under close scrutiny. Products produced by genetic engineering are
often derived from cells or organisms that do not normally produce these substances
(e.g. interferon production in bacteria) yet are intended for use in clinical applications.
It is therefore of paramount importance to determine what, if any, role is
played by protein bound carbohydrate. Parameters such as half-life in vivo, interaction
with receptors, immunogenicity and the like may all be affected. Surprisingly
enough, the armamentarium available for modifying carbohydrates in a predictable and
directed manner is scarce. Through detailed knowledge of glycan biosynthesis, opportunities
may be created to fill this gap.
This article deals with inhibitors of N-linked oligosaccharide processing. These
substances, most of which were described only recently, show promise of allowing the
manipulation of N-linked glycan structures in a rather precise manner, and hence
might be useful in investigations on the function of carbohydrates.
In order to describe the effects of these inhibitors in their proper context, a4
brief overview of N-linked glycan synthesis will be given. Subsequently, the literature
on the enzymes involved in N-linked glycan processing will be reviewed in some
detail. Since the effects of the inhibitors to be described need not be the same for
each of the enzymes involved even if these enzymes have very similar substrate specificities,
their description as possibly distinct targets for inhibition is called
for. The inhibitors of oligosaccharide trimming themselves will then be described in
detail. Finally, the concluding remarks will deal with some possible applications of
N-linked glycan processing inhibitors
TOWARDS CONFORMATIONAL SEQUENCING OF PROTEINS: ASSIGNMENT OF SECONDARY STRUCTURES BY ANTI-PEPTIDE ANTIBODIES
No full textWe performed model studies towards assignment of &-turn and a-helices to protein
primary structures with antibodies. Probing of a &-turn was attempted with anti-peptide
antibodies directed against the &-turn (DPGQ) of a synthetic &-turn model-peptide
(IVIVIDPGQTVTY) adopting the intended conformation &-sheet-&-turn-&-sheet. The
specific anti-&-turn model-peptide antibodies have a three orders of magnitude higher
affinity for the &-turn containing epitope than the control Gly-peptide (GsDPGQG,, ) of
random coil structure. The antibody affinity for the &-turn region (DPGQ) increases
from the primary to the hyperimmune response. Although the chosen &-turn sequence is
similar to parts of the animal's own proteins, self-tolerance did not raise difficulties
in generating antibodies against the R-turn model-peptide. Individual putative
&-turn sequences of proteins may be probed by including their sequence between the
two &-sheet cartridges of the &-turn model-peptide. Helix assignment was probed with
synthetic model peptides of extended conformation including only the superimposed
residues of a putative helix (every fourth residue) linked by a spacer amino acid
residue (alanine throughout or the corresponding third residue of the sequence to be
tested) in order to adjust the translation of the relevant residues of the model-peptide
to the helical pitch. The anti-helix modelpeptide antibodies were shown by
Western blotting to react in a sequence-specific manner with the corresponding model
protein lactose permease of E.coli. "Conformational sequencing" i.e. sequence
assignments of secondary structures by anti-peptide antibodies now seems feasable for
&-turn regions and helices of proteins of known sequence
PERVAPORATION, EINSATZMÖGLICHKEITEN EINES NEUEN MEMBRANVERFAHRENS IN DER BIOTECHNOLOGIE
No full textAufgrund der Möglichkeit, regenerierbare Rohstoffe zu verwenden, und der Verfügbarkeit
von optimierten Mikroorganismen wird der biotechnologischen Produktion von Grundchemikalien
die Chance eingeräumt, mit herkömmlichen Produktionsverfahren in Konkurrenz treten
zu können. Gerade bei der Produktion von Grundchemikalien spielt allerdings der technischwirtschaftliche
Aufwand zur Produktaufarbeitung eine entscheidende Rolle, so daß der
Entwicklung von Aufarbeitungsverfahren annähernd der gleiche Stellenwert zukommt wie der
Entwicklung der biotechnologischen Produktion.
Hier bietet sich für die Trennung von Flüssigkeitsgemischen ein relativ neues Membranverfahren,
nämlich die Pervaporation, an. Dabei kann ein homogenes Flüssigkeitsgemisch
aufgrund von unterschiedlicher Sorption und Diffusion der einzelnen Komponenten in einer
Membran getrennt werden. Die für den Stofftransport entscheidenden Faktoren, nämlich
Diffusionskoeffizienten und Löslichkeit der Flüssigkeitskomponenten in der Membran, sind
weitgehend Materialeigenschaften der Membran und lassen sich aus diesen vorhersagen, so
daß mit Hilfe von verschiedenen Modellvorstellungen eine gezielte Membranentwicklung für
ein bestimmtes Trennproblem möglich ist
IMMUNOSENSOR SYSTEMS USING LIPOSOMES AND PLANAR LIPID BILAYER MEMBRANES FOR ION-CHANNEL MODEL SENSORS
No full textFor the purpose of constructing a new biosensor which mimics the
concept of "ion-channel", two approaches were examined: l)liposome
systems, and 2)planar lipid bilayer membrane systems. In both cases,
some interaction such as immunoreaction, electrostatruneh dıpole,sand
hydrophobic interaction of a stimulus with a model receptor site at the
surface of lipid membranes triggers the change in permeation of marker
ions across the lipid bilayer membranes. This change in permeation of
the marker ions is subsequently monitored electrochemically, which is a
direct but much amplified measure of the analyte to be assayed
OPTICAL ION DETECTION VIA ION PAIRING
No full textAn important goal of our research is to develop reversible
indicator systems that selectively respond to both anions. One
approach is to based indicators on ion pairing reactions. Cation
detection systems include an uncharged immobilized ionophore, an
anionic dye and a cationic polyelectrolyte. The effect of added cation
is to cause the anionic dye to dissociate from the cationic
polyelectrolyte and form an ion pair with the ionophore/cation
complex. Here we review results for cations and present new results
for detection of an anion, fluoride. We have succeeded in developing
indicators that are reversible and selective. The biggest problem we
have encountered is slow response due to slow kinetics of the
processes required for response
AN AMPEROMETRIC GLUCOSE SENSOR WITH COMBINED ENZYME LAYERS
No full textAn amperometric needle-type glucose sensor (1) consisting of a silver tube (cathode)
and a platinum wire (anode) was developed. The sensor was provided with two enzyme
layers (glucose oxidase (GOD) in cellulose acetate, catalase). The destructive influence
of H,0, generated in the GOD layer could be minimized and the oxygen dependence
of the analytical signal was improved