The oxidation kinetics of thin nickel films between 250 and 500 °C.

The oxidation kinetics of thin polycrystalline Ni films is of fundamental interest as well as being relevant for potential applications. It was investigated between 250 and 500 °C for 10-150 nm thick films. Even for the thinnest films, oxidation was found to be diffusion controlled. The high density of grain boundaries in the formed NiO layer leads to a tracer diffusion coefficient that is higher than reported in the literature, indicating accelerated Ni diffusion along the grain boundaries. Cr segregation to the bottom interface in doped-NiO films hindered the acceleration of the oxidation of thin films.

Combined theoretical and experimental analysis of processes determining cathode performance in solid oxide fuel cells.

Solid oxide fuel cells (SOFC) are under intensive investigation since the 1980's as these devices open the way for ecologically clean direct conversion of the chemical energy into electricity, avoiding the efficiency limitation by Carnot's cycle for thermochemical conversion. However, the practical development of SOFC faces a number of unresolved fundamental problems, in particular concerning the kinetics of the electrode reactions, especially oxygen reduction reaction. We review recent experimental and theoretical achievements in the current understanding of the cathode performance by exploring and comparing mostly three materials: (La,Sr)MnO3 (LSM), (La,Sr)(Co,Fe)O3 (LSCF) and (Ba,Sr)(Co,Fe)O3 (BSCF). Special attention is paid to a critical evaluation of advantages and disadvantages of BSCF, which shows the best cathode kinetics known so far for oxides. We demonstrate that it is the combined experimental and theoretical analysis of all major elementary steps of the oxygen reduction reaction which allows us to predict the rate determining steps for a given material under specific operational conditions and thus control and improve SOFC performance.

Nonlinear electrical grain boundary properties in proton conducting Y-BaZrO3 supporting the space charge depletion model.

The overall proton conductivity of polycrystalline acceptor-doped BaZrO(3) is limited by the high resistivity of its grain boundaries. To investigate the nature of the electrical response of the grain boundaries as a function of the DC bias, Y-doped BaZrO(3) ceramics with a very large grain size (up to 200 µm) have been prepared in an infrared image furnace. The grains are so large that even individual grain boundaries can be addressed by microelectrodes. DC voltage-dependent resistance and capacitance of the grain boundaries are discussed in terms of the space charge model. The results corroborate carrier depletion (OH(O)˙, h˙, V(O)˙˙) as origin of the pronounced grain boundary resistance. This picture fits well into the space charge scenario found for various related oxide materials, and leads to strategies for improving grain boundary conductivity.

Immunocytochemical localization of mutant low density lipoprotein receptors that fail to reach the Golgi complex.

In the low density lipoprotein (LDL) receptor system, blocks in intracellular movement of a cell surface receptor result from naturally occurring mutations. These mutations occur in patients with familial hypercholesterolemia. One class of mutant LDL receptor genes (class 2 mutations) produces a receptor that is synthesized and glycosylated in the endoplasmic reticulum (ER) but does not reach the cell surface. These receptors contain serine/threonine-linked (O-linked) carbohydrate chains with core N-acetylgalactosamine residues and asparagine-linked (N-linked) carbohydrate chains of the high mannose type that are only partially trimmed. To determine the site of blockage in transport, we used electron microscope immunohistochemistry to compare the intracellular location of LDL receptors in normal human fibroblasts with their location in class 2 mutant fibroblasts. In normal cells, LDL receptors were located in coated pits, coated vesicles, endosomes, multivesicular bodies, and portions of the Golgi complex. In contrast, the mutant receptors in class 2 cells were almost entirely confined to rough ER and irregular extensions of the rough ER. Metabolic labeling studies with [3H]glucosamine confirmed that these mutant receptors contain core O-linked sugars, suggesting that the enzymes that attach these residues are located in the rough ER or the transitional zone of the ER. These studies establish that naturally occurring mutations in cell surface receptors can cause the receptors to remain trapped in the ER, thereby preventing their normal function and producing a genetic disease.

Laparoscopic sleeve gastrectomy achieves substantial weight loss in an adolescent girl with morbid obesity.

BACKGROUND: The European guidelines for bariatric surgery clearly define criteria for operating children with morbid obesity. However the appropriate technique for this age-group has not been identified yet. So far gastric banding and Roux-Y bypass represent the standards, but they demand life-long tolerance of either an artificial device or significant malabsorption. Although laparoscopic sleeve gastrectomy (LSG) demands neither, it has not been advocated for this age-group as a stand-alone technique. We report the outcome and the rationale for this approach in a 16-year-old girl with morbid obesity. MATERIAL AND METHOD: The patient had been in an intensive weight loss programme for several years, but within the last 12 months her body weight had increased again dramatically. At referral she presented with a body mass index (BMI) of 43.1 kg/m(2) (height 169 cm, preoperative weight 121 kg) and suffered from co-morbidities as features of a developing metabolic-vascular syndrome such as dyslipidemia and arterial hypertension. Our obesity team and her parents opted for surgery at that time. The patient underwent LSG with a 5-trocar technique. With a gastroscope protecting the lesser curvature, the stomach was resected from the antrum to the fundus using an EndoGIA stapler. The operative time was 95 minutes, there were no perioperative complications and the patient was extubated immediately. An upper GI contrast study on postoperative day 4 showed a tubular gastric remnant with a volume of about 200 ml. The patient's diet was advanced as tolerated to full oral intake, and she was followed-up regularly in our special obesity outpatient clinic. After 12 months she had lost 36 kg (BMI 29 kg/m(2)) and enjoyed sports and activities with friends again. Laboratory studies ruled out malnutrition or vitamin deficiency. CONCLUSION: LSG is a safe and effective option for bariatric surgery in obese adolescents. It can be offered as a stand-alone restrictive operation and could be extended to a malabsorptive procedure at any time. However longer follow-up is required before universally recommending this procedure.

Cloning, expression, purification, and characterization of the murine lysosomal acid alpha-mannosidase.

Catabolism of alpha-linked mannose residues on eukaryotic glycoproteins is accomplished by a broad specificity lysosomal alpha-mannosidase (EC 3.2.1.24). Based on regions of protein sequence conservation between the lysosomal alpha-mannosidase from Dictyostelium discoideum and the murine Golgi glycoprotein processing alpha 1,3/1,6-mannosidase, alpha-mannosidase II, we have cloned a cDNA encoding the murine lysosomal alpha-mannosidase. The longest of the clones was 3.1 kb in length and encoded a polypeptide of 992 amino acids containing a putative NH2-terminal signal sequence and 11 potential N-glycosylation sites. The deduced amino acid sequence was 76.5% identical to the human lysosomal alpha-mannosidase and 38.1% identical to the lysosomal alpha-mannosidase from D. discoideum. Expression of the cDNA in Pichia pastoris resulted in the secretion of an alpha-mannosidase activity into the culture medium. This recombinant expression product was purified and was shown to have enzymatic characteristics highly similar to the enzyme purified from mammalian sources and to the human lysosomal alpha-mannosidase cDNA expressed in Pichia. These characteristics include a similar pH optimum, Km, Vmax, inhibition by swainsonine, and activity toward natural substrates. Northern blots identified a major 3.5 kb RNA transcript in all murine tissues tested. A minor transcript of 5.4 kb was also detected in some murine tissues similar to the alternatively spliced transcripts that have been previously identified in human tissues.

The alpha-mannosidase of Trypanosoma cruzi: structure and function.

Trypanosoma cruzi alpha-mannosidase has been purified to apparent homogeneity. It is a 240,000-Da tetramer composed of four identical subunits (58,000 Da). Each subunit contains one N-linked high-mannose oligosaccharide. Based on pH optimum and sensitivity to inhibition by swainsonine, we suggest it to be lysosomal, but this has yet to be demonstrated directly. The enzyme appears to be developmentally regulated and may be a key enzyme in the degradation of the lipopeptidophosphoglycan (LPPG) during transformation from epimastigote to trypomastigote. Preliminary experiments suggest T. cruzi does not utilize the mannose 6-phosphate recognition system for sorting alpha-mannosidase (or other acid hydrolases) to the lysosome. To clone the alpha-mannosidase from T. cruzi we have used the same approach that has been used for other alpha-mannosidases. The cDNA amplification product was subcloned and sequenced. Comparison of the T. cruzi alpha-mannosidase sequence with the alpha-mannosidases that were used in the original primer design demonstrated a greater similarity to murine lysosomal and Dictyostelium alpha-mannosidases than to Golgi alpha-mannosidases.

The technical feasibility of cryonics.

Cryonic suspension is a method of stabilizing the condition of someone who is terminally ill so that they can be transported to the medical care facilities that will be available in the late 21st or 22nd century. There is little dispute that the condition of a person stored at the temperature of liquid nitrogen is stable, but the process of freezing inflicts a level of damage which cannot be reversed by current medical technology. Could this damage be reversed by future technology? We consider the limits of what medical technology should eventually be able to achieve (based on currently understood chemistry and physics) and whether the repair of frozen tissue is within those limits.

[Postoperative endoscopy for the diagnosis and therapy of complications]. / Postoperative Endoskopie zur Diagnose und Therapie von Komplikationen.

A variety of endoscopic methods are available as the main tools in the diagnostics and therapy of various complications after visceral and thoracic surgery. Indications for endoscopic interventions are anastomotic leaks, stenoses, Gl-tract bleedings, biliary lesions and functional problems after surgical procedures. The most common are fibrin sealing of fistulas, dilatation and bougienage, injection therapy for bleeding, bile duct interventions and stent implantations. In most cases operative revisions can be avoided by using endoscopic methods with an overall good success rate. No disadvantages are foreseen following conventional operative interventions if the endoscopic treatment is not successful.

[Conventional or laparoscopic cholecystectomy in treatment of acute cholecystitis?]. / Konventionelle oder laparoskopische Cholecystektomie zur Behandlung der akuten Cholecystitis?

Elective laparoscopic cholecystectomy has become established as the procedure of choice for the treatment of symptomatic cholecystolithiasis while the application of this method for acute cholecystitis has been propagated with restrainment. In a prospective study 114 conventional (right subcostal incision) and 102 laparoscopic cholecystectomies for this indication were compared. The overall complication rate amounted 10.7% for conventional cholecystectomy and 8.9% for laparoscopic cholecystectomy. The rate of conversion was 9.2%. Due to the fact that intraoperative cholangiography was carried out in 60% of conventional cholecystectomies and in only one of laparoscopic procedures the arithmetic advantage of minimally invasive technique with respect to blood loss and operating time does not allow final conclusions. These patients however recovered clearly faster and could be discharged after an average of 5.2 +/- 4.2 postoperative days, while the hospitalisation after conventional operations amounted to 7.6 +/- 3.8 days (p < 0.001).

Enzymatic sulfation of N-glycosidically linked oligosaccharides by endothelial cell membranes.

Homogenates of human vascular endothelial cells catalyze the transfer of 35SO4 from 3'-phosphoadenosine 5'-phospho[35S]sulfate into macromolecular endogenous acceptors with properties of both glycoproteins and glycosaminoglycans. Analysis of the 35S-glycoprotein products by both DEAE-cellulose chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that these 35S-glycoproteins correspond to the major sulfated glycoproteins observed when endothelial cell cultures were labeled with 35SO4 [A. Heifetz, C. Watson, A. R. Johnson, and M. K. Roberts (1982) J. Biol. Chem. 257, 13581-13586]. The pH optimum of the glycoprotein sulfotransferase is 7.0-7.5, which is distinctly different than that of endothelial glycosaminoglycan sulfotransferase(s), whose pH optimum is 6.0. The 35S-glycoprotein products were characterized as sialated, triantenary-branched, N-linked 35SO4-oligosaccharides containing an endo-beta-N-acetylglucosaminidase D-sensitive site. The site of sulfation was characterized as the GlcNAc residue on the reducing end of the N-linked oligosaccharide. Thus, these sulfotransferases in a cell-free homogenate appear to preferentially add sulfate moieties to a specific class of glycoprotein acceptors at a specific site on sialated oligosaccharides.

Localization of adenylate cyclase during development of Dictyostelium discoideum.

Cyclic AMP is known to function as the chemotactic signal during aggregation of single-celled amoebae of the cellular slime mold Dictyostelium discoideum. Evidence from several laboratories has accumulated suggesting that cAMP also acts as a regulatory molecule during Dictyostelium multicellular differentiation. We have used ultramicrotechniques and a sensitive radioimmunoassay in the localization of adenylate cyclase, the cAMP synthetic enzyme, during the development of Dictyostelium. We demonstrate that adenylate cyclase activity is localized in the prespore cells of the culminating individual with no activity detectable in the prestalk region. We show that this lack of activity in the stalk may be due to a masking by an endogenous inhibitor of the enzyme. Within the spore mass we found an increasing gradient of enzyme activity toward the base. These data, along with that from the localization of cyclic nucleotide phosphodiesterase, indicate that an enzymatic potential exists for the creation of cAMP gradients during development in the organism. Such a gradient may provide positional information necessary to direct the terminal differentiation of spore and stalk cells.

Asparagine-linked oligosaccharides containing poly-N-acetyllactosamine chains are preferentially bound by immobilized calf heart agglutinin.

We have investigated the carbohydrate-binding specificity of a mammalian lectin, calf heart agglutinin, by determining the interaction of the immobilized lectin with a variety of complex-type Asn-linked oligosaccharides. Our results demonstrate that calf-heart agglutinin binds with high affinity to oligosaccharides containing the repeating disaccharide (3Gal beta 1-4GlcNAc beta 1)n or poly-N-acetyllactosamine sequence and that the presence of terminal beta-linked galactosyl residues is neither sufficient nor necessary for high affinity interactions.

Relationship of the terminal sequences to the length of poly-N-acetyllactosamine chains in asparagine-linked oligosaccharides from the mouse lymphoma cell line BW5147. Immobilized tomato lectin interacts with high affinity with glycopeptides containing long poly-N-acetyllactosamine chains.

To investigate the factors regulating the biosynthesis of poly-N-acetyllactosamine chains containing the repeating disaccharide [3Gal beta 1,4GlcNAc beta 1] in animal cell glycoproteins, we have examined the structures and terminal sequences of these chains in the complex-type asparagine-linked oligosaccharides from the mouse lymphoma cell line BW5147. Cells were grown in medium containing [6-3H]galactose, and radiolabeled glycopeptides were prepared and fractionated by serial lectin affinity chromatography. The glycopeptides containing the poly-N-acetyllactosamine chains in these cells were complex-type tri- and tetraantennary asparagine-linked oligosaccharides. The poly-N-acetyllactosamine chains in these glycopeptides had four different terminal sequences with the structures: I, Gal beta 1,4GlcNAc beta 1,3Gal-R; II, Gal alpha 1,3Gal beta 1,4GlcNac beta 1,3Gal-R; III, Sia alpha 2,3Gal beta 1,4GlcNAc beta 1,3Gal-R; and IV, Sia alpha 2,6Gal beta 1,4GlcNAc beta 1,3Gal-R. We have found that immobilized tomato lectin interacts with high affinity with glycopeptides containing three or more linear units of the repeating disaccharide [3Gal beta 1,4GlcNAc beta 1] and thereby allows for a separation of glycopeptides on the basis of the length of the chain. A high percentage of the long poly-N-acetyllactosamine chains bound by immobilized tomato lectin were not sialylated and contained the simple terminal sequence of Structure I. In addition, a high percentage of the sialic acid residues that were present in the long chains were linked alpha 2,3 to penultimate galactose residues (Structure III). In contrast, a high percentage of the shorter poly-N-acetyllactosamine chains not bound by the immobilized lectin were sialylated, and most of the sialic acid residues in these chains were linked alpha 2,6 to galactose (Structure IV). These results indicate that there is a relationship in these cells between poly-N-acetyllactosamine chain length and the degree and type of sialylation of these chains.

[Does the lithotripter change gallstone surgery?]. / Andert der Lithotripter die Gallensteinchirurgie?

Extracorporeal shock-wave lithotripsy (ESWL) is a new method for treating gallstones. ESWL is an alternative method to cholecystectomy for treating symptomatic gallbladder stones--complicated cases excluded--in about 15% of all cases. The risk of stone recurrence with all its consequences (symptoms, complications, late mortality) has to be weighed against the higher morbidity and mortality of surgical treatment. ESWL can be used for bile duct stones instead of endoscopy. Concrements cannot be removed mechanically (10-20%) have been treated with a high success rate (80%) using ESWL. In summary, at present ESWL is restricted to a small number of selected cases.