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H Engelhardt

Publications and source records attributed to H Engelhardt.

96 records · Page 6Linked to original sources
PubMedDate not supplied

Topology of the anion-selective porin Omp32 from Comamonas acidovorans.

Limited proteolysis experiments were performed with outer membranes from Comamonas acidovorans to probe the topology of its major protein component, the anion-selective porin Omp32. Proteinase K treatment above a critical temperature of 42 degrees C cleaved the surface-exposed regions of the porin, yielding membrane-embedded fragments which were separated by SDS polyacrylamide gel electrophoresis or reversed phase chromatography. The identification of the proteinase K-sensitive sites was performed by microsequencing. This allowed us to determine six surface-exposed sites of the porin, all located in nonconserved primary structure regions. These results along with the previously determined amino acid sequence and in conjunction with some structural constraints applicable to porins allowed us to propose a chain-folding model of the Omp32 porin. The features of our model are compared with the structure of the Rhodobacter capsulatus porin, recently established by X-ray crystallography (Weiss et al., 1991) and they are used to elucidate the structural basis of the anion selectivity.

Amino Acid Sequence↗
PubMedDate not supplied

Viscoelastic properties of erythrocyte membranes in high-frequency electric fields.

The high deformability of erythrocytes which is essential for their transport through the capillaries depends critically on their discoid shape and on the elasticity of the plasma membrane, which may be determined by interactions of the cytoskeleton, the lipid/protein leaflet and the glycocalyx. Although techniques exist for measurement of the static elastic properties of erythrocytes, the cells are continuously deformed in vivo, the stress varying within periods of a few seconds. Thus dynamic elastic behaviour is essential for their physiological function. We present here a novel means of measuring the dynamic elastic constants of the red cell based on the transient deformation of individual cells in an inhomogeneous high-frequency (HF) electric field. By microscopy it is possible to record cellular elongations as small as 200 nm occurring within time scales of 1 ms. A main advantage is that the cellular response is linear and thus can be more readily interpreted theoretically. We have observed a creep function consisting of two exponentials with response times of 0.1 s and 1 s, which can be described in terms of a simple viscoelastic model. A remarkable temperature dependence of the membrane elasticity between 25 degrees C and 15 degrees C is observed for freshly drawn cells but not for trypsinized ones.

Elasticity↗
PubMedDate not supplied

Comparative studies on the significance of in vitro data of BCG vaccines.

In vitro parameters of BCG vaccine, such as colony-forming units or bacterial weight, are significant with respect to efficacy and occurrence of side effects only for vaccines which are made by one manufacturer according to one method and tested in one laboratory. With respect to colony-forming units from different products, widely varying doses must be applied to gain comparable effects. Similar effects can be expected from the human dose, recommended for each particular product. These conclusions, derived from experiences in vaccination against tuberculosis can also be considered essential for comparative immunotherapy with BCG vaccines.

BCG Vaccine↗
PubMedDate not supplied

Uterine natural killer cells in species with epitheliochorial placentation.

The epitheliochorial placenta represents the least intimate association between maternal and fetal tissues. The best known examples of this form of placentation are the domestic livestock species. Current information on the nature and proposed functions of uterine lymphocyte populations in ruminants (sheep and cattle), horses and pigs is presented. In ruminants unusual gamma delta T cells may play a role in mid to late gestation. During normal horse pregnancy, fetally derived endometrial cup cells invade the uterine stroma and are destroyed by maternal leukocytes midway through gestation. Natural killer (NK) cells or lymphokine-activated killer cells may be involved in this process, but the presence of these cell types in the equine uterus has yet to be established. The pig is similar to the human and rodent in that NK-like cells are present in the uterine stroma and seem to play a role in pregnancy. These cells are activated during early placental development and may be important in early interactions between the conceptus and the maternal immune system. The contribution of pregnancy-associated uterine lymphocytes to successful gestation has not been established. However, a common theme among these species is that the presence of the genetically foreign conceptus seems to activate uterine lymphocytes and to redirect their activities towards the promotion of fetal survival.

Animals↗
PubMedDate not supplied

Chiral separations with coated and uncoated capillaries.

Chiral resolution depends on the time the two enantiomers have for active migration within the capillary. Consequently, the magnitude of the electroosmotic flow (EOF) has a paramount influence on resolution, especially for chiral acidic compounds (counterosmotic migration). In this case, when the mobility of the analytes relative to that of the EOF is known, a rule of thumb can be deduced: Coated capillaries with suppressed EOF should be used when the effective mobility of the analyte is less than 50% of that of the EOF. Uncoated capillaries give better resolution when the effective mobility of the analyte is higher than 50% of that of the EOF because of the longer effective migration distance. The efficiencies achieved are mainly a function of the time the analytes spend in the capillary when solute-wall interactions can be neglected.

Amino Acids↗