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Biomedical subjects

M Frey

Publications and source records attributed to M Frey.

At least 109 records · Page 6Linked to original sources
PubMed1997

Tyrosine kinase-dependent regulation of L-selectin expression through the Leu-13 signal transduction molecule: evidence for a protein kinase C-independent mechanism of L-selectin shedding.

The L-selectin adhesion molecule mediates lymphocyte extravasation in peripheral lymph nodes, and has also been implicated in directing leukocyte recruitment to inflammatory tissues and metastasis of lymphoid malignancies. In this study, we demonstrate a novel level of regulation of L-selectin expression that involves the 16-kDa Leu-13 signal transduction molecule. Leu-13 is a member of a multimeric cell surface complex in lymphocytes that includes TAPA-1 (target of antiproliferative Ab-1, CD81) as well as lineage-specific proteins. In the present study, mAb-induced ligation of Leu-13 was shown to rapidly down-regulate L-selectin surface density on normal and malignant human lymphocytes, and to markedly inhibit L-selectin-mediated adhesion of lymphocytes to soluble carbohydrate ligands (i.e., PPME, phosphomonoester core polysaccharide) and to lymph node high endothelial venules. Through the use of genistein and staurosporine, potent inhibitors of tyrosine kinases (TK) and protein kinase C (PKC), respectively, Leu-13-induced L-selectin down-modulation was demonstrated to involve a TK-dependent, PKC-independent pathway, and was attributed to increased L-selectin shedding from surface membranes. Notably, direct L-selectin ligation, modeling cross-linking interactions with endothelial cell ligands, similarly down-regulates L-selectin surface expression through a TK-dependent, PKC-independent mechanism. In sharp contrast, PMA and anti-CD3 mAb down-regulate L-selectin via a staurosporine-sensitive, genistein-resistant pathway that is closely linked to lymphocyte proliferation. Taken together, these results demonstrate a novel role for Leu-13- and L-selectin-induced TK activity in control of L-selectin expression, thus providing insight into the complex molecular mechanisms that potentially regulate L-selectin-dependent lymphocyte homing in vivo.

Antigens, Differentiation↗
PubMed1997

Mechanistic insights into p53-promoted RNA-RNA annealing.

The tumour suppressor protein p53 promotes the annealing of complementary nucleic acids in vitro. We observed an up to 1600-fold increase of RNA-RNA annealing by recombinant p53 protein which was shown to bind to RNA in sequence-independent way. Nuclease mapping experiments suggest that p53 binds to intramolecular duplex portions and only marginally changes the overall secondary structure of RNA at conditions of increased annealing. Thus, the mechanism of p53-promoted RNA-RNA annealing does not seem to be dependent on an activity that melts or changes RNA structure. The activation enthalpy of RNA-RNA annealing is decreased in the presence of p53, i.e. the p53 protein could stabilize the transition state whereas the activation entropy is unfavourable. A comparison with thermodynamic data measured for other facilitators strongly suggests that the mechanism of p53-promoted RNA-RNA annealing is distinct from the mechanism by which other facilitators work. The annealing activity of p53 is almost abolished in the presence of magnesium indicating that it can be sharply regulated in vitro and, in principle, could also be regulated in vivo.

Escherichia coli↗
PubMed1997

Purification and characterization of an active form of the p78Rep protein of adeno-associated virus type 2 expressed in Escherichia coli.

The 78-kDa product (p78Rep) of the rep gene of AAV-2 was expressed with an amino-terminal histidine-tag in Escherichia coli and was purified under denaturing conditions. After renaturation of the p78Rep protein by serial steps of dialysis, the biochemical activities of the p78Rep protein were demonstrated, which include the ATP-dependent endonuclease and helicase activity as well as sequence-specific binding to the AAV-2 terminal repeat. These activities were retained when the protein was purified under denaturing conditions followed by renaturation. When compared with published data for p68Rep, the helicase activity of p78Rep was stronger and the endonuclease activity was weaker. The p78Rep protein was able to inhibit HIV-1 replication after co-microinjection together with infectious proviral HIV-1 DNA into the nuclei of human cells, suggesting that p78Rep is necessary for inhibition of HIV-1 in vivo.

Cell Line↗
PubMed1997

Effects of long-term hypergravity on muscle, heart and lung structure of mice.

Quantitative changes in lung, heart and muscle structure were assessed in mice exposed for 14 weeks to a gravitational field of 3 G since the age of 4 weeks; matched controls were kept at normal gravity (1 G). The body mass of 3-G-exposed mice was significantly reduced by 9%, while total skeletal muscle mass remained the same fraction of body mass. The mass of the soleus muscle was found to be significantly larger in 3-G-exposed mice both in absolute (+27%) and body mass specific terms (+42%). Capillary density was significantly reduced by 22% because of a relatively larger increase of fiber cross-sectional area (+47%) than of capillary to fiber ratio (+16%). Other morphometric variables remained unchanged with hypergravity. Heart mass and mitochondrial volume were both larger in 3-G-exposed mice (+15% and +27%, respectively). This difference reached statistical significance when normalized to body mass. The only significant difference in lung structure detectable by morphometric methods were a smaller volume (-9%), that paralleled lower body mass, and thinner alveolar septa (-12%). From these results it is concluded that the lung's support structures in mice are sufficiently strong to withstand the stress of long-term hypergravity; however, 3-G exposure leads to a selective hypertrophy of soleus muscle fibers while absolute capillary length in this muscle remains unaltered.

Adaptation, Physiological↗
PubMed1997

The influence of the graft length on the functional and morphological result after nerve grafting: an experimental study in rabbits.

Clinical experience shows that the results after the use of long nerve grafts for reconstruction are sometimes poor. Nevertheless several authors have stressed that the concomitant big defect in the soft tissues necessitating the use of long grafts is the reason for some of the failures. In 22 rabbits the saphenous nerve was used as a nerve graft. Animals were separated into 3 groups with different lengths of the grafts, namely 3 cm (group 1), 5 cm (group 2) and 7 cm (group 3). In the left hindlimb the proximal end of the graft was coapted to the cut motor nerve branch of vastus medialis. In a second stage the distal end of the graft was coapted to the nerve branch of rectus femoris. After a total period of 15 months the maximum tetanic tension in the reinnervated rectus femoris and in the contralateral unoperated muscle was determined. Biopsies of the graft and the motor branch distal to the graft were taken in order to count the number of regenerated myelinated nerve fibers. The average maximum tetanic tension in the rectus femoris muscle reinnervated by the 3 cm long graft was 27.2 N, in group 2 the force was 20.5 N. In group 3 the maximum force was 17.6 N, which meant an average loss of 29% compared to the contralateral unoperated muscle. The mean number of regenerated myelinated fibres distal to the graft in the rectus femoris motor branch was 1683 in group 1 and decreased to 1137 in group 3. The results show that the length of the graft influences the results after nerve grafting to a certain extent, but a combination of other factors like concomitant soft tissue injury and destroyed target organs may also be responsible for some of the poor results after the clinical use of long nerve grafts.

Animals↗
PubMed1997

Hydrogenase: a hydrogen-metabolizing enzyme. What do the crystal structures tell us about its mode of action?

Hydrogenases are proteins which metabolize the most simple of chemical compounds, molecular hydrogen, according to the reaction H2<-->2H+ + 2e-. These enzymes are found in many microorganisms of great biotechnological interest such as methanogenic, acetogenic, nitrogen fixing, photosynthetic or sulfate-reducing bacteria. The X-ray structure of a dimeric [NiFe] hydrogenase together with a wealth of biophysical, biochemical and genetic studies have revealed that the large subunit contains the bimetallic [Ni-Fe] active site, with biologically uncommon CO and CN ligands to the iron, whereas the small subunit contains three iron-sulfur cluster. During catalysis, the nickel atom is most likely responsible for a base-assisted heterolytic cleavage of the hydrogen molecule whereas the iron atom could be redox active. Specific channels are probably required for the transfer of the chemical reaction partners (H2, H+ and e-) between the active site, deeply buried inside the protein, and the molecular surface. The generation of a functional enzyme, including the assembly of the complex catalytic center, requires maturation and involves a large number of auxiliary proteins which have been partly characterized by molecular biology.

Crystallography, X-Ray↗
PubMed1997

Questions of the handsurgeon to the radiologist--a survey on the most common lesions in the hand and the implications of diagnostic tools on their therapy.

By the rapid development of imaging techniques, a significant gap developed between the knowledge of the radiologists and that of the hand surgeons on specific indications of the different technical possibilities. The problems to be solved by both specialties together are analyzed. Examples of the most common lesions in the hand like trauma, reflex sympathetic dystrophy, congenital malformation, infection, tumour, rheumatoid and other degenerative processes, nerve compression syndromes etc., are given, and the implications of diagnostic tools on their therapy are discussed.

Hand↗
PubMed1997

Gas access to the active site of Ni-Fe hydrogenases probed by X-ray crystallography and molecular dynamics.

The 2.54 A resolution structure of Ni-Fe hydrogenase has revealed the existence of hydrophobic channels connecting the molecular surface to the active site. A crystallographic analysis of xenon binding together with molecular dynamics simulations of xenon and H2 diffusion in the enzyme interior suggest that these channels serve as pathways for gas access to the active site.

Binding Sites↗
PubMed1997

[Comparative studies of morphometric and functional results following reconstruction of motor nerves].

In order to determine the value of a reconstructive procedure in the peripheral nerve, experimental studies often evaluate the number and the diameter of myelinated nerve fibers as a parameter for the quality of regeneration. This study addresses the correlation between the number of fibers in a peripheral motor nerve after microsurgical reconstruction and the functional result, expressed as the force of the reinnervated muscle. In a total number of 24 sheep, the motor branch to the rectus femoris muscle was severed. The muscle was reinnervated either by direct neurorrhaphy or by nerve grafting, performed in three different ways (free grafting to the ipsilateral muscle, free grafting to the contralateral muscle, vascularized grafting to the ipsilateral muscle). In the final experiments, the muscle force in the reinnervated muscle was determined by supramaximal electrical stimulation. Number and diameter of myelinated nerve fibers were evaluated by computer-assisted morphometric analysis. Regression analysis of morphometric data and the muscle forces was calculated. No correlation was found between fiber numbers in the nerve graft and the maximal force. However, a positive correlation between the number of myelinated fibers in the motor branch distal to the site of coaptation and the functional result was observed in some cases. The diameter of myelinated fibers had no influence on the functional outcome.

Animals↗
PubMed1996

X-ray structure of the ferredoxin:NADP+ reductase from the cyanobacterium Anabaena PCC 7119 at 1.8 A resolution, and crystallographic studies of NADP+ binding at 2.25 A resolution.

The crystal structure of the ferredoxin:NADP+ reductase (FNR) from the cyanobacterium Anabaena PCC 7119 has been determined at 2.6 A resolution by multiple isomorphous replacement and refined using 15.0 A to 1.8 A data, collected at 4 degrees C, to an R-factor of 0.172. The model includes 303 residues, the flavin adenine dinucleotide cofactor (FAD), one sulfate ion located at the putative NADP+ binding site and 328 water molecule sites. The structure of Anabaena FNR, including FAD, a network of intrinsic water molecules and a large hydrophobic cavity in the C-terminal domain, resembles that of the spinach enzyme. The major differences concern the additional short alpha-helix (residues 172 to 177 in Anabaena FNR) and residues Arg 100 and Arg 233 which binds NADP+ instead of Lys 116 and Lys 244 in the spinach enzyme. Crystals of a complex of Anabaena FNR with NADP+ were obtained. The model of the complex has been refined using 15 A to 2.25 A X-ray data, collected at -170 degrees C, to an R-factor of 0.186. This model includes 295 residues, FAD, the full NADP+ (with an occupancy of 0.8) and 444 water molecules. The 2'-5' adenine moiety of NADP+ binds to the protein as 2'-phospho-5'-AMP to the spinach FNR. The nicotinamide moiety is turned towards the surface of the protein instead of stacking onto the FAD isoalloxazine ring as would be required for hydride transfer. The model of the complex agrees with previous biochemical studies as residues Arg 100 and Arg 233 are involved in NADP+ binding and residues Arg77, Lys 53 and Lys 294, located on the FAD side of the enzyme, remain free to interact with ferredoxin and flavodoxin, the physiological partners of ferredoxin: NADP reductase.

Amino Acid Sequence↗
PubMed1996

[Ambulatory surgery in clinical practice: limits and possibilities].

Prerequisites for outpatient surgery performed by primary care physicians are fundamental anatomic knowledge and basic surgical skill. A precise clinical and functional examination of the affected area must precede every wound care, treatment of infection or excision of a skin lesion. The surgical procedure and postoperative care must be determined and discussed with the patient. Lesions with defect and lesions of neurovascular structures as well as deep infections of the hand, stab and bite wounds must be taken care of by a specialist. Histologic examination of excised skin lesions is mandatory. Malignant melanomas have to be considered by a interdisciplinary treatment regimen.

Ambulatory Surgical Procedures↗
PubMed1996

[Breast reconstruction].

The changes in the rationale of surgical therapy of breast cancer led to increased importance of plastic and reconstructive surgery in this field. Besides the development of surgical procedures for breast-conserving surgery, plastic surgery was mainly responsible for the popularization of primary or secondary breast reconstruction, based on several scientific studies, showing no negative effect of breast reconstruction on the oncological course. Also, for defect reconstruction in advanced cases, flaps are indispensable for improvement of the local situation. Further, reduction mammaplasty can be of prophylactic value by significant gland tissue reduction. For breast reconstruction, autologous tissue is of increasing importance, since silicone breast implants have been discredited by a long-lasting media campaign. The best results are achieved with the transverse rectus abdominis myocutaneous flap. In patients with small breasts, the latissimus dorsi myocutaneous flap without prosthesis should be preferred.

Breast↗
PubMed1996

Free jejunum transfers for functional reconstruction after tumour resections in the oral cavity and the pharynx: changes of morphology and function.

Oropharyngeal reconstruction following resections for locally advanced carcinoma by free jejunum transfer was studied in 31 consecutive cases over a period of 6 years, from 1988-1994. The most common site was the hypopharynx (n = 23). Reconstruction of the tonsillar region was performed in 5 cases and of the inner lining of the mouth in 5 cases. Two patients underwent neoglottic reconstruction, creating a tracheo-pharyngeal shunt. By use of an exteriorized jejunal segment for flap monitoring changes in morphology and function of a microvascular transferred denervated segment of jejunum could be monitored. The success rate was 94%. No evidence of fistula formation and local dehiscence were experienced in this series. Histological examinations showed some fibrotic changes 6 months after transplantation; lubrication and motility of the transplant were not severely altered. Biosynthesis, processing, and proteolytic activity of the jejunal epithelial cells were not impaired 2 weeks postoperatively.

Carcinoma, Squamous Cell↗
PubMed1996

Role of a muscle target organ on the regeneration of motor nerve fibres in long nerve grafts: a synopsis of experimental and clinical data.

The importance of the muscle target organ as a promoting factor for nerve fibre regeneration in nerve grafts is still a subject of controversial discussion. In the last few years we published uniform results of experimental series in sheep and rabbits in which we investigated the biology of nerve fibre regeneration in long nerve autografts without connection to a target organ. Surprisingly, we found excellent regeneration of myelinated nerve fibres without the influence of a target organ through the whole length of the nerve graft, with an increase in the number of nerve fibres up to fourfold at the distal end. In the sheep series the additional contact with a muscle target organ for 6 months had a variable effect on the fibre population in the distal end of the nerve graft. The results of our planimetric analyses of nerve biopsies in patients with facial paralysis, who were treated by cross-face nerve grafting and free muscle transplantation, are extremely divergent from the results of our experimental series. Instead of an increase, we found a decrease in number of regenerating nerve fibres arriving at the distal end of the cross-face nerve graft down to 20%. Species-specific differences in the biology of nerve regeneration are discussed, together with their implications for the complex clinical situation of nerve grafting with or without the influence of a target organ.

Anastomosis, Surgical↗
PubMed1996

Scutuloauricularis muscle of the rabbit: a new model for free functional muscle transplantation in the mimic system.

There is little information on the specific process of free, functional muscle transplantation to the face trying to restore mimic function. Up to now one of the main reasons was the impossibility of functional assessment of mimic muscles as well as their transplanted substitutes. The scutuloauricularis muscle provides an ideal model for quantitative assessment of muscle function because of its circumscript tendinous insertion and is suitable for microsurgical transplantation. In a series of 26 adult, female New Zealand rabbits the anatomical and microsurgical details were studied. The scutuloauricularis muscle weighs 1.018 +/- 0.106 g, it is supplied by the auricularis rostralis artery (diameter 0.4 +/- 0.1 mm) and the auricularis rostralis vein (diameter 1.3 +/- 0.1 mm) and one oligofascicular (2-3 fascicles) branch of the facial nerve. During isometric contraction under supramaximal electrostimulation the maximal tetanic tension was 2.995 +/- 0.928 N. Histomorphometric studies in ATP-ase stained cross-sections showed 40.5 +/- 4.6% type I fibres, 32.3 +/- 5.2% type IIA fibres, and 27.2 +/- 7.1% type IIB fibres.

Animals↗
PubMed1996

Behavioral correlates of health and illness in youths with chronic illness.

Relationships between and among general health behavior, illness management behavior, indicators of health (functional, physical/mental, and perceived health status) and indicators of illness (duration, control, and perception of severity) were compared across five samples of youth with either insulin dependent diabetes mellitus (IDDM) or asthma. Descriptive data indicated that youths performed approximately 72% of the health and illness management behaviors recommended by health professionals. General health behavior and illness management behavior were significantly related (r = .39 to .62; p < .05). General health behavior was more consistently related to indicators of health (r = .37 to .62; p < .001) than to indicators of illness. Illness management behavior was not related to indicators of illness either. However, illness management behavior was significantly related to higher perception of health status (r = .35, .48; p < .001). Interestingly, there were no relationships between health and illness indicators. These findings challenge nurses to address general health behavior as well as illness management in practice and to raise questions as to whether illness management improves illness status or if illness status influences health status when health is viewed from a nursing perspective. Knowing the links between behavior and relevant health and illness outcomes will facilitate identification and movement toward goals of improved health and may account for intervention failure.

Adaptation, Psychological↗
PubMed1996

Novel metal sites in protein structures.

Recently, the three-dimensional structures of several novel metalloenzymes have been solved. Of special interest are those containing uncommon and/or not well characterized metals such as molybdenum, tungsten, nickel, vanadium and cobalt. Modulated by the protein environment, the specific properties of these metals and of special metal-binding cofactors such as siroheme and topa quinone are used to catalyze a vast array of fascinating reactions.

Binding Sites↗