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.

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.

[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.

Cloning, expression, purification, and characterization of the acid alpha-mannosidase from Trypanosoma cruzi.

The acid alpha-mannosidase of Trypanosoma cruzi is a broad-specificity hydrolase involved in the catabolism of glycoconjugates, presumably in the digestive vacuole. We have cloned the alpha-mannosidase gene from a T.cruzi epimastigote genomic library. The alpha-mannosidase gene was determined to be single copy by Southern analysis, and similar sequences were not detected in genomic digests of either Trypanosoma brucei or Leishmania donovani. The coding region was subcloned into the Pichia pastoris expression vector pPICZ, and alpha-mannosidase activity was detected in the medium of induced cultures. The recombinant alpha-mannosidase demonstrated a pH optimum, inhibition by swainsonine, Km, and substrate specificity consistent with the characteristics of the alpha-mannosidase previously purified from T.cruzi epimastigotes. The recombinant enzyme was purified 103-fold from the culture medium of Pichia pastoris and had a native molecular mass of 359 kDa by gel filtration. A combination of SDS-PAGE, deglycosylation with endo H, and NH2-terminal sequencing indicates that the enzyme is originally synthesized as a homodimeric polypeptide that is subsequently cleaved to form a heterotetramer composed of 57 and 46 kDa subunits. A polyclonal antibody raised to the recombinant enzyme was shown to immunoprecipitate the alpha-mannosidase from T.cruzi cell extracts and will be used in future immunolocalization studies.

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.

Isolation and characterization of a class II alpha-mannosidase cDNA from lepidopteran insect cells.

Lepidopteran insect cells are used routinely as hosts for foreign glycoprotein expression by recombinant baculoviruses, but the precise nature of their N-glycosylation pathway remains poorly defined. These cells clearly have processing glucosidases and mannosidases that can convert precursors to Man3GlcNAc2 structures and fucosyltransferases that can add fucose to the oligosaccharide core. However, their ability to extend these structures to produce complex side chains like those found in mammalian cells remains to be determined. To begin to examine this pathway at the molecular genetic level, we isolated and characterized a class II alpha-mannosidase (alpha-mannosidase II) cDNA from Sf9, a lepidopteran insect cell line. In mammalian cells, this enzyme catalyzes the committed step in the pathway converting N-linked carbohydrates to complex forms. Degenerate primers against conserved regions in known class II alpha-mannosidase protein sequences were used to generate an alpha-mannosidase II-specific PCR product from Sf9 cell DNA. Sequence information from this product was used to isolate a partial cDNA clone, the 5' end was isolated by ligation-anchored PCR, and the full length alpha-mannosidase II cDNA was assembled. This cDNA contained a long open reading frame predicted to encode an 1130 amino acid protein with 37% identity to human Golgi alpha-mannosidase II and with a type II membrane topology, a feature of all known Golgi processing enzymes. Southern blotting indicated that alpha-mannosidase II is a single copy gene in Sf9 cells. Other Lepidoptera had related alpha-mannosidase II genes, but there was variation among different genera, and the Sf9 alpha-mannosidase II cDNA did not cross-hybridize with DNA from animals outside Lepidoptera. Steady-state levels of alpha-mannosidase II RNA were low in uninfected Sf9 cells and even lower after baculovirus infection. The in vitro-translated Sf9 alpha-mannosidase II protein had the expected size and was translocated and N-glycosylated by microsomal membranes. Expression of the Sf9 alpha-mannosidase II cDNA in the baculovirus system produced large amounts of a protein with the expected size and swainsonine-sensitive alpha-mannosidase II activity towards an aryl-alpha-mannoside substrate. These results demonstrate that Sf9 cells encode and express an alpha-mannosidase II with properties similar to those of the mammalian enzyme.

[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).

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.

Complex-type N-linked oligosaccharides of gp120 from human immunodeficiency virus type 1 contain sulfated N-acetylglucosamine.

The major envelope glycoproteins gp120 and gp41 of human immunodeficiency virus type 1, the causative agent for human AIDS, contain numerous N-linked oligosaccharides. We report here our discovery that N-acetylglucosamine residues within the complex-type N-linked oligosaccharides of both gp120 and its precursor, gp160, are sulfated. When human Molt-3 cells persistently infected with human T-cell leukemia virus IIIB were metabolically radiolabeled with 35SO4, gp160, gp120, and to some extent gp41 were radiolabeled. The 35SO4-labeled oligosaccharides were quantitatively released by N-glycanase treatment and were bound by immobilized Ricinus communis agglutinin I, a lectin that binds to terminal beta-galactosyl residues. The kinetics of release of sulfate upon acid hydrolysis from 35SO4-labeled gp120 indicate that sulfation occurs in a primary sulfate ester linkage. Methylation analysis of total glycopeptides from Molt-3 cells metabolically radiolabeled with [3H]glucosamine demonstrates that sulfation occurs at the C-6 position of N-acetylglucosamine. Fragmentation of the gp120-derived 35SO4-labeled glycopeptides by treatment with hydrazine and nitrous acid and subsequent reduction generated galactosyl-anhydromannitol-6-35SO4, which is the expected reaction product from GlcNAc-6-sulfate within a sulfated lactosamine moiety. Charge analysis of the [3H]galactose- and [3H]glucosamine-labeled glycopeptides from gp120 and gp160 indicates that approximately 14% of the complex-type N-linked oligosaccharides are sulfated.

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.

gp160 of HIV-I synthesized by persistently infected Molt-3 cells is terminally glycosylated: evidence that cleavage of gp160 occurs subsequent to oligosaccharide processing.

The envelope glycoprotein of HIV-I in infected, cultured human T cells is synthesized as a precursor of apparent Mr 160 kDa (gp160) and is cleaved to two glycoproteins, gp120 and gp41, which are the mature envelope glycoproteins in the virus. Neither the temporal and spatial features of glycosylation nor the oligosaccharide processing and proteolytic cleavage of the envelope glycoprotein are well understood. To understand more about these events, we investigated the glycosylation and cleavage of the envelope glycoproteins in the CD4+ human cell line, Molt-3, persistently infected with HIV-I (HTLV IIIB). The carbohydrate analysis of gp160 and gp120 and the behavior of the glycoproteins and glycopeptides derived from them on immobilized lectins demonstrate that both of these glycoproteins contain complex- and high-mannose-type Asn-linked oligosaccharides. In addition, the N-glycanase-resistant oligosaccharides of gp120 were found to contain N-acetyl-galactosamine, a common constituent of Ser/Thr-linked oligosaccharides. Pulse-chase analysis of the conversion of [35S]cysteine-labeled gp160 showed that in Molt-3 cells it takes about 2 h for gp120 to arise with a half-time of conversion of about 5 h. At its earliest detectable occurrence, gp120 was found to contain complex-type Asn-linked oligosaccharides. Taken together, these results indicate that proteolytic cleavage of gp160 to gp120 and gp41 occurs either within the trans-Golgi or in a distal compartment.

The dysfunctional LDL receptor in a monensin-resistant mutant of Chinese hamster ovary cells lacks selected O-linked oligosaccharides.

The Chinese hamster ovary (CHO) cell line Monr31, which is resistant to the cytotoxic ionophore monensin, produces a receptor for the low density lipoprotein (LDL) that has a lowered binding affinity for LDL and is approximately 5 kDa smaller in size than the receptor from parental CHO cells. It has been proposed that the reduced size and affinity for LDL are associated with a reduced level of O-glycosylation of Ser/Thr residues in the receptor. To examine this possibility in more detail, both parental CHO and Monr31 cells were metabolically radiolabeled with [3H]glucosamine, and the labeled LDL receptors were purified by immunoprecipitation and identified by SDS-PAGE-fluorography. The Ser/Thr-linked oligosaccharides in the receptors from both parental CHO and Monr31 cells are mono- and desialylated species having the common core structure Gal beta 1-3GalNAc. The receptor from Monr31 cells, however, contains about one-third fewer Ser/Thr-linked oligosaccharides than the receptor from parental CHO cells. Analysis of the glycopeptides derived from the Monr31 cell LDL receptors indicates that they contain Ser/Thr-linked oligosaccharides only in the clustered domain and are missing Ser/Thr-linked oligosaccharides in the unclustered regions of the protein. Additionally, analysis of a human LDL receptor lacking the domain for attachment of the clustered Ser/Thr-linked oligosaccharides and expressed in both parental CHO and Monr31 cells indicated that the truncated human receptor from Monr31 cells is devoid of Ser/Thr-linked oligosaccharides. In contrast, the truncated human receptor produced by parental CHO cells contains Ser/Thr-linked oligosaccharides contributing approximately 5 kDa to its apparent size. Collectively, these results demonstrate that the LDL receptor produced by the Monr31 cells contains Ser/Thr-linked oligosaccharides in the clustered domain but is missing Ser/Thr-linked oligosaccharides in the unclustered, NH2-terminal domains of the receptor.

Characterization of an S-type lectin purified from porcine heart.

We have purified a carbohydrate-binding protein from porcine heart by affinity chromatography on asialofetuin-Sepharose and have characterized this protein with respect to its size, amino acid composition, partial amino acid sequence, and carbohydrate-binding specificity. Porcine heart lectin (PHL) has a subunit molecular mass of 14,700 and is immunologically cross-reactive with a polyclonal antibody raised against a lectin isolated from calf heart. The amino acid composition of PHL is similar to that of lectins that have been isolated from calf heart, bovine brain, and rat lung. Moreover, the primary sequences of four tryptic fragments (52 amino acids total) derived from PHL are closely related to sequences previously determined for 10 other vertebrate-derived lectins. The ability of PHL to agglutinate rabbit erythrocytes was inhibited only by oligosaccharides containing terminal beta-galactosyl residues. These data indicate that PHL is a vertebrate "S-type" lectin and provide further evidence that the structures and carbohydrate-binding specificities of these lectins are highly conserved across diverse vertebrate genera.

[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.