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A Krebs

Publications and source records attributed to A Krebs.

At least 19 recordsLinked to original sources
PubMed1998

Characterisation of an improved two-dimensional p22121 crystal from bovine rhodopsin.

Dialysis of rhodopsin isolated from bovine rod outer segments resulted in the formation of a new two-dimensional crystal form suitable for electron crystallography. The crystals obtained were tubular or single layers and showed p22121 symmetry (a=60.6(+/-0.8) A, b=86.3(+/-1.6) A). For the first time the size and order of the crystals allowed us to take electron diffraction patterns showing spots to a resolution of about 3.5 A. Images were recorded at liquid nitrogen temperature using a high voltage field emission electron microscope. Out of a large number of images 20 crystalline areas were selected and processed with the MRC image processing software. A projection structure of bovine rhodopsin to 5 A resolution was calculated using amplitudes and phases extracted from these images. The achieved resolution exceeds the resolution of all previously obtained structures of frog, bovine and squid rhodopsin crystals. In this map small differences are observed compared to the previous maps. Helix 5 seems to be even more highly tilted and between the arc-shaped feature and helix 5 a peak is present suggesting that helix 3 is prolonging this feature towards helix 5. These observations are in agreement with the latest model for the three-dimensional arrangement of rhodopsin. The resolution achieved as well as the availability of electron diffraction data suggest that there is a good possibility to collect data from tilted crystals and calculate an improved three-dimensional structure of rhodopsin.

Animals↗
PubMed1998

Lumbricus terrestris hemoglobin: a comparison of small-angle x-ray scattering and cryoelectron microscopy data.

The quaternary structure of Lumbricus terrestris hemoglobin was investigated by small-angle x-ray scattering (SAXS). Based on the SAXS data from several independent experiments, a three-dimensional (3D) consensus model was established to simulate the solution structure of this complex protein at low resolution (about 3 nm) and to yield the particle dimensions. The model is built up from a large number of small spheres of different weights, a result of the two-step procedure used to calculate the SAXS model. It accounts for the arrangement of 12 subunits in a hexagonal bilayer structure and for an additional central unit of clylinder-like shape. This model provides an excellent fit of the experimental scattering curve of the protein up to h = 1 nm-1 and a nearly perfect fit of the experimental distance distribution function p(r) in the whole range. Scattering curves and p(r) functions were also calculated for low-resolution models based on 3D reconstructions obtained by cryoelectron microscopy (EM). The calculated functions of these models also provide a very good fit of the experimental scattering curve (even at h > 1 nm-1) and p(r) function, if hydration is taken into account and the original model coordinates are slightly rescaled. The comparison of models reveals that both the SAXS-based and the EM-based model lead to a similar simulation of the protein structure and to similar particle dimensions. The essential differences between the models concern the hexagonal bilayer arrangement (eclipsed in the SAXS model, one layer slightly rotated in the EM model), and the mass distribution, mainly on the surface and in the central part of the protein complex.

Animals↗
PubMed1997

alpha-1,4-D-glucan phosphorylase of gram-positive Corynebacterium callunae: isolation, biochemical properties and molecular shape of the enzyme from solution X-ray scattering.

The alpha-1,4-D-glucan phosphorylase from gram-positive Corynebacterium callunae has been isolated and characterized. The enzyme is inducible approx. 2-fold by maltose, but remarkably not repressed by D-glucose. The phosphorylase is a homodimer with a stoichiometric content of the cofactor pyridoxal 5'-phosphate per 88-kDa protein subunit. The specificity constants (kcat/Km, glucan) in the directions of glucan synthesis and degradation are used for the classification of the enzyme as the first bacterial starch phosphorylase. A preference for large over small substrates is determined by variations in the apparent binding constants rather than catalytic-centre activities. The contribution of substrate chain length to binding energy is explained assuming two glucan binding sites in C. callunae phosphorylase: an oligosaccharide binding site composed of five subsites and a high-affinity polysaccharide site separated from the active site. A structural model of the molecular shape of the phosphorylase was obtained from small-angle solution X-ray scattering measurements. A flat, slightly elongated, ellipsoidal model with the three axes related to each other as 1:(0.87-0.95):0.43 showed scattering equivalence with the enzyme molecule. The model of C. callunae phosphorylase differs from the structurally well-characterized rabbit-muscle phosphorylase in size and axial dimensions.

Animals↗
PubMed1996

Lack of size and shape alteration of oxygenated and deoxygenated Lumbricus terrestris hemoglobin?

The giant extracellular hemoglobin of Lumbricus terrestris was investigated in the oxygenated, deoxygenated and reoxygenated state using small angle X-ray scattering. Scattering experiments of the oxygenated state of the protein yielded a radius of gyration of 10.71 +/- 0.02 nm, a maximum diameter of 29.37 +/- 0.21 nm and a volume of 6200 +/- 200 nm3. The values for the deoxygenated state of the hemoglobin are smaller than the values for the oxygenated state, but the differences hardly exceed the limits of error.

Animals↗
PubMed1996

Molecular shape, dissociation, and oxygen binding of the dodecamer subunit of Lumbricus terrestris hemoglobin.

Small angle x-ray scattering of the 213-kDa dodecamer of Lumbricus terrestris Hb yielded radius of gyration = 3.74 +/- 0.01 nm, maximum diameter = 10.59 +/- 0.01 nm, and volume = 255 +/- 10 nm3, with no difference between the oxy and deoxy states. Sedimentation velocity studies indicate the dodecamer to have a spherical shape and concentration- and Ca2+-dependent equilibria with its constituent subunits, the disulfide-bonded trimer of chains a-c and chain d. Equilibrium sedimentation data were fitted best with a trimer-dodecamer model, ln K4 = 7 (association K in liters3/g3) at 1 degrees C and 4 at 25 degrees C, providing DeltaH = -20 kcal/mol and DeltaS = 4.4 eu/mol. Oxydodecamer dissociation at pH 8.0, in urea, GdmCl, heteropolytungstate K8[SiW11O39] and of metdodecamer at pH 7, was followed by gel filtration. Elution profiles were fitted with exponentially modified gaussians to represent the three peaks. Two exponentials were necessary to fit all the dissociations except in [SiW11O39]-8. Equilibrium oxygen binding measurements at pH 6.5-8. 5, provided P50 = 8.5, 11.5-11.9 and 11.9-13.5 torr, and n50 = 5.2-9. 5, 3.2-4.9, and 1.8-2.7 for blood, Hb, and dodecamer, respectively, at pH 7.5, 25 degrees C. P50 was decreased 3- and 2-fold in approximately 100 mM Ca2+ and Mg2+, respectively, with concomitant but smaller increases in cooperativity.

Animals↗
PubMed1996

Mutational analysis of the Epstein-Barr virus nuclear antigen 2 by far-Western blotting and DNA-binding studies.

We have previously shown by far-Western blotting that the Epstein-Barr virus nuclear antigen 2 (EBNA-2) both binds to a cellular protein of 130 kDa and histone H1, with the complex between EBNA-2 and p130 being tighter than between EBNA-2 and histone H1. Here we demonstrate that the N terminus of EBNA-2, which was previously shown to be necessary for transformation of B lymphocytes by EBNA-2, is essential for binding to p130. We further show data indicating that the binding of EBNA-2 to histone H1 appears not to be mediated exclusively via the basic Arg-Gly rich region in the C-terminal part of EBNA-2. With a MAb directed against the Trp-Trp322-Pro (WWP) motif of EBNA-2, which is known to be essential for the interaction of EBNA-2 with the cellular factor RBPJkappa/CBF1, we could inhibit the DNA binding of EBNA-2, providing further evidence that this region of EBNA-2 forms direct contact with RBPJkappa/CBF1.

Amino Acid Sequence↗
PubMed1995

Provocation of hypotension during head-up tilt testing in subjects with no history of syncope or presyncope.

BACKGROUND: Head-up tilt test is increasingly being used to evaluate patients with syncope. This study was designed to evaluate the specificity of head-up tilt testing using different tilt angles and isoproterenol infusion doses in normal volunteers with no prior history of syncope or presyncope. METHODS AND RESULTS: One hundred fifty volunteers were randomized to two groups of 75 each. In group 1, subjects were further randomized to have head-up tilt testing at a 60, 70, or 80 degree angle at baseline followed by repeat tilt testing during a low-dose isoproterenol infusion that increased the heart rate by an average of 20%. In group 2, after having a baseline head-up tilt test at a 70 degree angle for a maximum of 20 minutes, subjects were randomized to have a repeat tilt table testing at a 70 degree angle during a low-dose, 3 micrograms/min, or 5 micrograms/min isoproterenol infusion. In group 1, syncope or presyncope along with hypotension developed in 2 subjects during the baseline test at 60 and 70 degrees of tilt and in 5 subjects during tilting at 80 degrees. The addition of low-dose isoproterenol reduced the specificity minimally from 92% to 88% at both 60 and 70 degrees of tilt but substantially to 60% at an 80 degrees angle. However, 6 of the 10 subjects with a positive test at an 80 degree angle had an abnormal response after 10 minutes of tilt testing. In group 2, using various isoproterenol doses with tilt table testing at a 70 degree angle, low-dose (mean infusion dose, 1.5 +/- 0.45 microgram/min), 3 micrograms/min, and 5 micrograms/min isoproterenol infusions elicited an abnormal response in 1 (4%), 5 (20%), and 14 (56%) of the subjects, respectively. Using multiple logistic regression analysis, head-up tilt testing at an 80 degree angle (P = .01) or during 3 micrograms/min (P = .02) and 5 micrograms/min isoproterenol infusion rates (P < .001) was the most significant predictor of an abnormal response. CONCLUSIONS: Head-up tilt testing at a 60 or 70 degree angle with or without low-dose isoproterenol infusion provides an adequate specificity. Caution is needed, however, in interpreting the results if the head-up tilt test at 80 degrees is extended beyond 10 minutes or if high doses of isoproterenol are used.

Adult↗
PubMed1995

[Endonasal implantation of a silicon mold improves the long-term outcome of revision surgery in lacrimal duct stenoses].

BACKGROUND: Uncomplicated dacryocystorhinostomy after dacryocystitis with lacrimal sac obstruction has a success rate of 85%. However therapy of restenosis poses a problem. Vast destruction of lacrimal and nasal mucosa renders the drainage system susceptible for further stenosis. This article presents a new surgical procedure for the treatment of restenosis of the nasolacrimal apparatus. The major difference from other techniques is the endonasal implantation of a silicon foil. This counters the development of synechiae and promotes the epitheliasation of wound surfaces. As a result the nasal mucosa can easier gain access to lacrimal mucosa. A complete mucosal coating of the reconstructed lacrimal drainage system is an important condition for the sufficient drainage of the tear-film. PATIENTS AND METHODS: In 30 patients with restenosis after one or multiple dacryocystorhinostomies a silicon foil was implanted endonasally as part of their surgical revision. After skin incision and removal of scar tissue the bony ostium was enlarged. The canaliculi were intubated with silastic tubing. Afterwards the endonasal synechiae were split and a 0.2-0.4 mm silicon foil was implanted endonasally und fixed. The silastic tubing was brought through a hole in the silicon foil and knotted inside the nose. Then the wound was closed. Postoperative evaluation of the surgical success ranged from 3 to 36 months (mean 16 months). RESULTS: The postoperative result was good in 24 patients. Sixteen patients were without symptoms. 8 had epiphora only on stress. The latter felt their situation to be greatly improved. The long-term results were directly proportional to the amount of reconstructable mucosa and inversely proportional to the severity of canaliculus damage. Adverse reaction to the silicon foil were not noted. CONCLUSION: Endonasal implantation of a silicon foil is a new, easy and successful technique for the treatment of endonasal synechiae and restenosis of the nasolacrimal apparatus.

Adolescent↗
PubMed1994

Binding of D-galactose-terminated ligands to rabbit asialoglycoprotein receptor.

The binding affinities of a series of D-galactose-terminated glycerol glycosides and oligosaccharides for the asialoglycoprotein receptor isolated from rabbit liver were determined in vitro using a radioreceptor-inhibition assay with 125I-asialoorosomucoid. The relative affinities of the synthetic ligands increased with the number of exposed D-galactose termini. Of the compounds examined, 1,2,3-tri-O-beta-lactosylglycerol associated with the greatest affinity (estimated Kd = 7.97 x 10(-5) M). Examination of the affinities of the synthetic series indicated that both the number and propinquity of the D-galactose termini influenced the strength of the binding interactions.

Animals↗
PubMed1992

Synthesis and characterization of 6-O-beta-lactosyl-alpha,beta-lactoses, 1-O-(6-O-beta-lactosyl-beta-lactosyl)-(R,S)-glycerols, and 4,6-di-O-beta-D-galactopyranosyl-alpha,beta-D-glucoses.

1,2,3,2',3',4',6'-Hepta-O-acetyl-beta-lactose (4) was coupled with 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (7) in the presence of Hg(CN)2 to afford 1,2,3,2',3',4',6'-hepta-O-acetyl-6-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-b eta- lactosyl)-beta-lactose (11) which, upon O-deacetylation, gave 6-O-beta-lactosyl-alpha,beta-lactoses (64% from 4). In contrast, the reaction of 7 with benzyl 2,3,2',3',4',6'-hexa-O-acetyl-beta-lactoside in the presence of Hg(CN)2 produced 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O- (2,3,2',3',4',6'-hexa-O-acetyl-1-O-benzyl-beta-lactos-6-yl orthoacetyl)-alpha-lactose (63%) and 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O-(1- cyanoethylidene)-alpha-lactose (27%). The glycosidation of 4 using 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide in the presence of Hg(CN)2 afforded, after deprotection, 4,6-di-O-beta-D-galactopyranosyl-alpha,beta-D-glucoses (66%). The reaction of 11 with 1,2-di-O-benzyl-(R,S)-glycerols and trimethylsilyl trifluoromethanesulfonate yielded, after deprotection, 1-O-(6-O-beta-lactosyl-beta-lactosyl)-(R,S)-glycerols (18%). Under the same coupling conditions 11 reacted with 2-O-benzylglycerol to form 3-O-acetyl-2-O-benzyl-1-O-[2',3',4',6'-hexa-O-acetyl-6-O-(2,3,6,2',3',4' ,6'- hepta-O-acetyl-beta-lactosyl)-beta-lactosyl]-(R,S)-glycerols (16%).

Asialoglycoprotein Receptor↗
PubMed1991

Synthesis and characterization of 2-O-beta-lactosylglycerol, 1,2-di-O-beta-lactosyl-(R,S)-glycerols, and 1,2,3,-tri-O-beta-lactosylglycerol.

The reaction of 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (5) and 1,3-di-O-benzylglycerol in the presence of mercury(II) cyanide in benzene-nitromethane afforded 1,3-di-O-benzyl-2-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)glyc erol (70%), which was converted into 2-O-beta-lactosylglycerol. 1,2-Di-O-beta-lactosyl-(R,S)-glycerols were obtained by way of the coupling of 5 to either 1-O-benzyl-(R,S)-glycerol or 1-O-benzyl-2-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)-(R,S)-gl ycerols. The most efficient route to 1,2, 3-tri-O-beta-lactosylglycerol (17) involved treatment of 2-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)glycerol with 3 mol. equiv. of 5 followed by removal of the blocking groups, to give 17 (47%).

Carbohydrate Sequence↗
PubMed1991

Synthesis and characterization of 6-O-beta-lactosyl-alpha,beta-D-mannopyranoses and 2,6-di-O-beta-lactosyl-alpha,beta-D-mannopyranoses.

The reaction of 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (4) and benzyl 3,4-di-O-benzyl-alpha-D-mannopyranoside (3) in the presence of mercury(II) cyanide in benzene-nitromethane produced benzyl 3,4-di-O-benzyl-2,6-bis-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lact osy l)-alph a D-mannopyranoside (5) and benzyl 3,4-di-O-benzyl-6-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)-alp ha-D- mannopyranoside (6), as part of a complex mixture. Column chromatography, followed by acetylation of the fraction containing 5 and 6, gave a sample of 5 and benzyl 2-O-acetyl-3,4-di-O-benzyl-6-O (2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)-alpha-D-mannopyranoside (7) in approximately 35% and 17% yields (based on 4), respectively. Deprotection of 5 and 7 afforded the target compounds, namely 2,6-di-O-beta-lactosyl-alpha,beta-D-mannopyranoses and 6-O-beta-lactosyl-alpha,beta-D-mannopyranoses, respectively. If the coupling of 4 with 3 were performed in the presence of silver trifluoromethanesulfonate and 2,4,6-trimethylpyridine, only a mixture of 3,6,2',3',4',6'-hexa-O-acetyl- alpha-lactose-1,2-[( 3,6,2',3',4',6'-hexa-O-acetyl-alpha-lactose 1,2-(benzyl 3,4-di-O-benzyl-alpha-D-mannopyranosid-6-yl orthoacetyl)-2-yl]orthoacetate) and 3,6,2',3',4',6'-hexa-O-acetyl-alpha-lactose 1,2-(benzyl 3,4-di-O-benzyl-alpha-D-mannopyranosid-6-yl orthoacetate) was obtained. The orthoacetates were characterized by n.m.r. spectroscopy. The two target materials are useful in the assessment of the binding properties of galactose-terminated ligands to the asialoglycoprotein receptor of normal rabbit and human hepatocytes.

Carbohydrate Sequence↗
PubMed1991

Elevated serum neopterin levels in atherosclerosis.

Plasma levels of neopterin were determined in patients with different clinical stages of atherosclerosis. Non-hospitalized patients with atherosclerosis had serum and plasma neopterin levels within the normal range of the assay (6 +/- 2 nM). These values were not significantly different from those reported for healthy blood donors (5 +/- 2 nM). In contrast, about 50% (29 out of 61) of hospitalized patients undergoing conservative or surgical therapy had neopterin plasma levels, which exceeded the normal range (greater than 10 nM) up to 10-fold. The two groups differ on a significance level of P less than 0.01. For further evaluation hospitalized patients were subgrouped according to neopterin levels. In the subgroup with elevated neopterin levels patients with higher Frederickson types of atherosclerosis were overrepresented compared to patients with normal neopterin levels. Type 4 differed significantly from patients without pathological changes of lipoprotein (P less than 0.05). Only 3 patients suffered from minimal skin necrosis, two of them had elevated neopterin levels. Significantly more patients with peripheral artery occlusions had elevated neopterin levels than patients with occlusions of central arteries (P less than 0.05). All other criteria used for comparison (sex, age, smoking, antioxidant status, diabetes, hypertension, adipositas, hyperuricemia) did not vary significantly in both subgroups. These data indicate that neopterin plasma levels might be a valuable parameter in activity staging and therapeutic follow up of atherosclerotic patients. Additionally, an involvement of the nonspecific immune system in atherogenesis is suggested by the increased plasma neopterin concentrations.

Aged↗
PubMed1990

Synthesis and characterization of new 10-acylderivatives of the antipsoriatic agent dithranol: coupling products of dithranol with all-trans-retinoic acid, 13-cis-retinoid acid and an aromatic analogue of retinoic acid: all-trans-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl- nona-2,4,6,8-tetraenoate.

The synthesis of new 10-acylderivatives of dithranol 1 is described. Compound 1 was reacted with the acid chlorides of all-trans retinoic acid 5, 13-cis-retinoic acid 6 and all-trans-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-nona-2,4,6,8- tetraenoate 7 in toluene and collidin as a base to give the coupling products 2, 3 and 4. The different structures were confirmed by high resolution 1H- and 13C-NMR spectroscopy. Initial investigations with the enzyme glucose-6-phosphate dehydrogenase indicate that all of them are inhibitors of the protein and therefore might have antipsoriatic activity.

Acitretin↗
PubMed1990

[Synthesis and biochemical properties of new 10-acyl derivatives of dithranols: acetylsalicyldithranol and 1-acetyllactyldithranol].

By reaction of the corresponding acid chlorides of acetylsalicylic acid (8) and L-acetyllactic acid (5) with dithranol (1) in toluene and collidin or pyridine as a base two new 10-acylderivatives of (1) were prepared: L-acetyllactyldithranol (2) and acetylsalicyldithranol (3). Both derivatives strongly inhibited the enzyme glucose-6-phosphate dehydrogenase, indicating possible antipsoriatic activity.

Anthralin↗
PubMed1990

[Synthesis, characterization, racemation and biochemical studies on 10-acylderivatives of chrysarobin: sorbylchrysarobin, beta-carbethoxypropionylchrysarobin and senecioylchrysarobin].

The racemic synthesis of three 10-acylderivatives of chrysarobin (1) is described. Senecioylchrysarobin (3), beta-carbethoxypropionylchrysarobin (4) and sorbylchrysarobin (5) were prepared by reaction of (1) with the corresponding carboxylic acid chlorides and collidine as a base in toluene. The separation of the racemates of (3) and (5) on a chiral stationary phase is demonstrated for the first time. All of the new compounds showed an increased potency of inhibition of the enzyme glucose-6-phosphate dehydrogenase, an indication for possible antipsoriatic activity.

Anthracenes↗