Helmholtz Zentrum für Infektionsforschung Repository
Not a member yet
4806 research outputs found
Sort by
GRAPHITE BASED BIENZYME SENSORS
No full textRobust peroxidase/oxidase sensors based on both chemically modified and unmodified graphite
electrodes were prepared. The sensorsacted atelectrode potentials of -0.2 V to 0.2 V vs Ag/AgCl
electrode. The Sensors werespecific to glucose, alcohols, choline chloride, L- and D-amino acids and
oxalic acid. The sensitivities of sensors ranged from 0.3 - 12 uA/mM and the determination ranges
of metabolites were 0.01 - 20 mM. The concentration range of cholesterine determined using a
hydrogen peroxide sensor and soluble cholesterol oxidase was 0.01 - 0.26 mM with a sensitivity of
0.25 mA/mM whendetermination was carried out using the in biocatalytic pre-concentration regime.
The pH optima andthe longterm stabilities of the sensors depended largely on the properties of the
oxidase immobilize
Algorithmic Representation of Large RNA Folding Landscapes
No full textIn evolutionary processes on the molecularlevel, neutral alterations play an important role
[Kim83]. The primary sequence of a DNA or RNA moleculeis changed by errors introduced
by the replication machinery at certain rates. Such a mutation does not necessarily
affect the phenotype. The molecule’s contribution to the individual’s overall fitness is
mediated by its function. For non-encoding RNA, the function in turn is determined by
the 3D-structure of the molecule. A mutation in the primary sequence of such an RNA
molecule that does notalter its structure is called neutral
Data set heterogeneities and their effects on the derivation of contact potentials
No full textA new class of protein structure prediction methods bases on threading a sequence through
a known 3D structure. These techniques offer a means of recognizing similarity in cases
of distant evolutionary relationship, where the fold has been conserved to a greater extent
than its sequence. The scoring table(s) which are used to evaluate different sequence to
structure alignments are derived from a particular database of known structures. The
distribution and the reliability of the threading scores is effected by parameters of this
database, such as length and composition of the included chains, and the number of
alternative alignments.
Weinvestigated several compositional aspects of two databases which were used in protein
fold recognition studies. Among them are the numberof chains from different folding
classes, the amino acid distribution within the classes, and the sequence lengths
BIOSYNTHESIS OF CONTACTINHIBIN A PLASMAMEMBRANE GLYCOPROTEIN INVOLVED IN CONTACT-DEPENDENT INHIBITION OF GROWTH
No full textGrowth of normal diploid human fibroblasts jn vitro is mainly
regulated by cell-cell-contacts.
We have isolated a 60 - 70 kDa plasma membrane Blycoprotein, named
Contactinhibin, which igs involved in the Process of contactinhibition
and inhibits the growth of sparsely seeded cells in a
concentration dependent, reversible and non toxic manner.
Antibodies raised against Contactinhibin released confluently seeded
cells from contact-inhibition, while sparsely seeded cells were not
affected. The cells treated with anti-Contactinhibin antibodies showed
a criss-cross morphology similar to transformed cells.
Here we describe the appearance of biosynthetic precursor molecules of
Contactinhibin after specific blocking of biosynthesis at an early
stage
PURIFICATION, GLYCOSYLATION AND SECRETION OF A REPRESSIBLE ACID PHOSPHATASE OF Yarrowia lipolytica
No full textA repressible acid phosphatase of Yarrowia lipolytica was purified and antibodies directed againstits
proteic portion wereobtained (1). Immunoprecipitation experiments have madeit clear that this enzyme
is very heterogeneous. Suchexperiments have also led to the detection of a precursor of about 86 kDa
in cells grown under conditions of derepression. This precursor corresponds to a partially glycosylated
form of the enzyme. The heterogeneity shown bythe enzyme is due toits oligosaccharidic component
since a single sharp band of 58-60 kDa appears when the immunoprecipitates of the cellular extracts
are treated with endo H. When the extracts from derepressed cells treated with tunicamycin were
immunoprecipitated with the antibodies, two polypeptides of 54 and 52 kDa appeared. Preliminary
experimental evidence supports the idea that these must be the mature non-glycosylated enzymatic
protein and its precursor containing the signal sequence. Under normal conditions of derepression, cells
secrete a glycosylated polypeptide into the culture medium, whereasin the Presenceof tunicamycin
two polypeptides of 38 and 20 kDa, whicharerelated immunologically to phosphatase, are detected
in the culture medium
CRYSTALLIZATION OF GASTRIC LIPASES
No full textGastric lipases are pH resistant enzymes with a molecular weight of ca 50,000,
including 15% sugars. Every glyco-variant from different species have been purified
by ief, and submitted to crystallization, using parameters found by an incomplete
factorial analysis method. All attempts were successful, but most crystals were
unsuitable to X-ray studies due to huge cell dimensions. Dog gastric lipase crystals,
the most suitable for X-ray study (pH 6.8, 12% PEG 6000, 20°C; P2242 :182A,
211A, 98 A), contain ca 8 molecules in the asymetric unit , and therefore diffract to
only 4A on lab sources
X-RAY STRUCTURE ANALYSIS OF GEOTRICHUM CANDIDUM LIPASE AT 2.8 A RESOLUTION
No full textGeotrichum candidum (ATCC 34614) produces extracellular lipase upon
submerged cultivation. With conventional purification techniques, the
enzyme was easily purified to apparent homogeneity, as judged from disc-
PAGE, isoelectric focusing and ultracentrifiugation. It was easily
crystallized by concentration, and low resolution X-ray analysis was done
on the crystals. However, we have quite recently found that the apparently
pure lipase was a mixture of two isozymes, both composed of 544 amino acids
and 6.5% carbohydrate. The two isozymes were separated from each other by
hydrophobic interaction chromatography. An X-ray analysis at 2.8 A
resolution has been undertaken onthe main fraction. The main chain was
tentatively followed. The whole enzyme molecule consists of a single domain
of 50 x 50 x 70 A, and contains 9 a-helices and 2 g-sheets
Chemical Modification of the Porcine Pancreatic Lipase
No full textIn this low-scope review we summarized the results which typically have not been publishedyet as
full papers. To our opinion these data could be valuable for the discussion of the recently published
[1] three-dimensional structure of human pancreatic lipase optained by the X-ray crystallography
studies.
The effect of the modification of several residues in porcine pancreatic lipase has been studied
primarily in terms of changes in the steady-state kinetics binding and rate constants which could be
determined in the assay system containing lipase (L), variable amounts ofcolipase (C), micellar
NaTDC! (bs) and excess of tributyrylglycerol emulsion (S). The approach is based on the
assumption that the enzyme does not have anyactivity in the presence of micellar NaTDC and
absence ofcolipase due to the displacementof the enzyme from the substrate-water interphase [2,
3], and hasbeen first used by Rathelot etal. [4, 5]. This assumption is correct provided that traces
of colipase have been removed from lipase preparations (on a Sephadex LH-60 column [6]).
Formally, since the observed dissociation constant of the lipase/colipase interfacial complex, K,””, is typically
less, or comparable, with the total enzyme concentration. In conditions K,*? >> [L], Eqn. 2
reduced to a common hyperbolic (Michaelis-type) relationship
Substrate Specifity Of Porcine Pancreatic Lipase Studied In Terms Of The Steady-State Kinetics Binding And Rate Constants
No full textThe steady-state kinetics binding constants have been rarely determined for emulsified lipase
substrates since the apparent Michaelis constant has the dimension of the emulsion surface area in
this case [1,2] which typically could not be determined precisely. On the other hand, only a
combination of binding and rate parameters could be determined in experiments with substrate
monolayers [3,4], and the range of suitable substratesis strictly limited in these experiments due to
requirements on the stability of monolayers, productsolubility, etc. [4].
In this paper we review data on the substrate specificity of porcine pancreatic lipase on emulsified
triacylglycerolsubstrates studied in terms of the steady-state binding and rate constants in the assay
system lipase/colipase/micellar NaTDC'/-triacylglycerol emulsion’
UREA BIOSENSOR BASED ON AN AMMONIA GAS PROBE USING AN NH4+-SENSITIVE PVC-ISE
No full textThe low cost urea biosensor presented here is based on the detection of
ammonia which is generated by an enzymatic reaction in the presence of urea.
Therefore an ammonia gas sensor is used which consists of a potentiometric
NH;-electrode with a modified PVC membranecovered by a gas membrane