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W Helfrich

Publications and source records attributed to W Helfrich.

At least 37 records · Page 2Linked to original sources
PubMed1994

Detection of a putative 30-kDa ligand of the cluster-2 antigen.

The cluster-2 antigen, also called EGP-2, is a 38-kDa transmembrane glycoprotein with a distribution that is largely confined to human epithelial cells and their derived carcinomas. Monoclonal antibodies (MAbs) directed against EGP-2 have been extensively studied as anti-tumor agents, yet the function of the antigen is not known. In the present study we used a biotinylated recombinant soluble derivative of the EGP-2 (sEGPbio) as a probe to detect a possible EGP-2 ligand, using various carcinoma cell lines as a substrate. The recombinant soluble EGP-2 was expressed in the Autographa californica nuclear polyhedrosis virus (baculovirus) expression system. The sEGP-2, to which we engineered a poly-histidine affinity tag, was purified from infected Spodoptera frugiperda insect cells using immobilized metal-ion-affinity chromatography (IMAC). In Western blot analysis the sEGPbio probe bound to a 30-kDa protein band in 2 out of 5 of the assessed carcinoma cell lines, suggesting that this band may be an EGP-2 ligand. Interestingly, binding only occurred when, prior to SDS-PAGE, cell lysates had been subjected to a reducing agent (2-mercapto-ethanol). The physiological significance of this phenomenon and nature of the detected 30-kDa protein band remains to be determined.

Amino Acid Sequence↗
PubMed1993

Special features of phosphatidylcholine vesicles as seen in cryo-transmission electron microscopy.

Vesicles of egg yolk phosphatidylcholine (EYPC) were studied by cryo-transmission electron microscopy. The electron micrographs indicate that, despite the rapidity of cooling, membrane undulations are flattened and some vesicles change their shapes before the samples freeze. These artefacts are attributed to the action of the lateral tension that results from the membrane area contraction associated with the temperature drop. Other micrographs represent grainy membranes and angular vesicles. We regard them as the first direct evidence for the superstructure and optically invisible roughness which were recently postulated for these membranes.

Dimyristoylphosphatidylcholine↗
PubMed1992

A discordance between the human muscle NCAM sequence and those seen in other NCAM cDNA clones.

A cDNA clone, designated NC7, has been isolated from human foetal kidney that partially codes for the 140 kDa isoform of human NCAM. This clone contains a 6 bp insert that is not present in the human muscle cDNA clone lambda 4.4. This same sequence has also been found in both a cDNA clone obtained from a human Small Cell Lung Carcinoma (SCLC) line and in human genomic DNA. Furthermore, an equivalent sequence to the 6 bp region identified in the above samples is present in mouse, rat and chicken NCAM. The 6 bp insertion does not lie at a predicted intron/exon boundary as extrapolated by homology studies with the chicken and, therefore, the mechanism by which the sequence is deleted from the human muscle clone lambda 4.4 remains unclear.

Amino Acid Sequence↗
PubMed1992

Splicing of the VASE exon of neural cell adhesion molecule (NCAM) in human small-cell lung carcinoma (SCLC).

Expression of the neural cell adhesion molecule (NCAM) on small-cell lung carcinoma (SCLC) cell lines and tumour tissue has been investigated. Cell lines were found to express highly sialylated NCAM. Neuraminidase treatment revealed the presence of the 140- and 120-kDa isoforms with differential expression of a 95-kDa protein. Similar data were obtained with SCLC tumour tissues. These results were corroborated by Northern blotting where mRNA of 6.7 and 5.5 kb coding for the 140- and 120-kDa isoforms, respectively, were identified. In a few tumours, a weaker band of 7.4-kb mRNA coding for the 180-kDa NCAM was also identified. This result could not be confirmed biochemically due to shortage of material. Finally, a 5-kb transcript was identified in all SCLC samples examined. The NCAM isoform coded by this mRNA remains unknown. Using the polymerase chain reaction (PCR), we have demonstrated the presence of the VASE mini-exon in some isoforms of SCLC NCAM. The VASE mini-exon sequence in human SCLC differs from the published murine sequence by only one base change. This substitution does not result in altered amino-acid sequence.

Amino Acid Sequence↗
PubMed1984

Ureteral obstruction secondary to perianeurysmal fibrosis.

Ureteral obstruction secondary to perianeurysmal fibrosis is rare. We have added 3 cases to the 61 cases previously reported in the literature. Perianeurysmal fibrosis should be included in the differential diagnosis of ureteral obstruction particularly when there is medial deviation of the ureters. Abdominal ultrasound is a valuable screening test to confirm the presence of perianeurysmal fibrosis. Treatment must be individualized for each patient, but the majority of patients will benefit most from preoperative urinary drainage followed by aneurysmectomy and ureterolysis.

Aged↗
PubMed1984

Magnetic anisotropy of lecithin membranes. A new anisotropy susceptometer.

Cylindrical giant vesicles prepared from egg lecithin and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are oriented in an external magnetic field and observed by phase contrast microscopy. The anisotropic part of the diamagnetic susceptibility of the lecithin membrane is determined from the distribution of angles between the magnetic field and the long cylinder axis due to thermal fluctuations. The anisotropy of DMPC is found to be larger by a factor of 2 than that of egg lecithin. This is attributed to the presence of unsaturated acyl chains in egg lecithin.

Chemical Phenomena↗
PubMed1981

Osmotic shrinkage of giant egg-lecithin vesicles.

Osmotic shrinkage of giant egg-lecithin vesicles was observed by phase-contrast microscopy. The vesicles remained or became spherical when shrinking. Small and thick-walled vesicles formed visible fingers attached to the sphere. The water permeability of the single bilayer was found to be 41 micrometers/s. A variety of observations indicate that osmosis induces a parallel lipid flow between the monolayers of the bilayer, leading to a strong positive spontaneous curvature. They also suggest the formation of mostly submicroscopic daughter vesicles. The estimated coupling constant, 2 . 10(-6) mol/mol, is large enough to be biologically significant.

Lipid Bilayers↗
PubMed1978

Magnetic anisotropy of egg lecithin membranes.

Magnetic realignment and rotational diffusion of cylindrical egg lecithin vesicles were measured under a phase contrast microscope. The anisotropy of magnetic susceptibility times membrane thickness was calculated from the data for several thin-walled vesicles. The resulting values were assigned to discrete numbers of bilayers. The difference between the susceptibilities parallel and perpendicular to the long axes of the lecithin molecules is deduced to be X parallel - X perpendicular = -(0.28 +/- 0.02) . 10(-8) cgs at 23 degrees C, if a bilayer thickness of 60 A is assumed.

Magnetics↗
PubMed1976

Red blood cell shapes as explained on the basis of curvature elasticity.

Assuming that the shape of red blood cells is controlled by the curvature elasticity of the surrounding membrane, we fit theoretical shapes to the contours Evans and co-workers determined by interference microscopy. Very good agreement is obtained for disc shapes. The fit is not so good for less common shapes, which may result from Evans' parametric representation and from the interference of shear elasticity.

Elasticity↗