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S Larsen

Publications and source records attributed to S Larsen.

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

Active site of dihydroorotate dehydrogenase A from Lactococcus lactis investigated by chemical modification and mutagenesis.

The flavin-containing enzyme dihydroorotate dehydrogenase (DHOD) catalyzes the oxidation of dihydroorotate (DHO) to orotate, the first aromatic intermediate in pyrimidine biosynthesis. The first structure of a DHOD, the A form of the enzyme from Lactococcus lactis, has recently become known, and some conserved residues were suggested to have a role in the active site [Rowland et al. (1997) Structure 2, 239-252]. In particular, Cys 130 was hypothesized to work as a base, which activates dihydroorotate (DHO) for hydride transfer. By chemical modification and site-directed mutagenesis we have obtained results consistent with this proposal. Cys 130 was susceptible to alkylating reagents, and mutants of Cys 130 (C130A and C130S) showed hardly detectable enzyme activity at pH 8.0, while at pH 10 the C130S mutant enzyme had approximately 1% of wild-type activity. Mutants of Lys 43, Asn 132, and Lys 164 were also constructed. Exchange of Lys 43 to Ala or Glu (K43A and K43E) and of Asn 132 to Ala (N132A) affected both catalysis and substrate binding. Expressed as kcat/KM for DHO, the deterioration of these three mutant enzymes was 10(3)-10(4)-fold. Flavin spectra of the mutant enzymes were not, like the wild-type enzyme, bleached by DHO in stopped-flow experiments, showing that they were deficient with respect to the first half-reaction, namely reduction of FMN by DHO, which was not rate limiting for the wild-type enzyme. The binding interaction between flavin and the reaction product, orotate, could be monitored by a red shift of the flavin absorbance in the wild-type enzyme. The C130A, C130S, and N132A mutant enzymes displayed similar capacity to bind orotate. In contrast, orotate did not change the absorption spectra of the K43 mutant enzymes, although it did inhibit their activity. All of the mutant enzymes, except K164A, contained normal levels of flavin. The results are discussed in relation to the structures of DHODA and other flavoenzymes. The possible acid-base chemistry of Cys 130 is compared to previous work on mammalian dihydropyrimidine dehydrogenases, flavoenzymes, which catalyze the reversed reaction, namely the reduction of pyrimidine bases.

Alkylating Agents↗
PubMed1997

The Mars Pathfinder atmospheric structure investigation/meteorology (ASI/MET) experiment.

The Mars Pathfinder atmospheric structure investigation/meteorology (ASI/MET) experiment measured the vertical density, pressure, and temperature structure of the martian atmosphere from the surface to 160 km, and monitored surface meteorology and climate for 83 sols (1 sol = 1 martian day = 24.7 hours). The atmospheric structure and the weather record are similar to those observed by the Viking 1 lander (VL-1) at the same latitude, altitude, and season 21 years ago, but there are differences related to diurnal effects and the surface properties of the landing site. These include a cold nighttime upper atmosphere; atmospheric temperatures that are 10 to 12 degrees kelvin warmer near the surface; light slope-controlled winds; and dust devils, identified by their pressure, wind, and temperature signatures. The results are consistent with the warm, moderately dusty atmosphere seen by VL-1.

Atmosphere↗
PubMed1997

Crystallization and preliminary X-ray diffraction analysis of the heterotetrameric dihydroorotate dehydrogenase B of Lactococcus lactis, a flavoprotein enzyme system consisting of two PyrDB subunits and two iron-sulfur cluster containing PyrK subunits.

Dihydroorotate dehydrogenases are flavin-containing enzymes which catalyze the conversion of (S)-dihydroorotate to orotate. Dihydroorotate dehydrogenase B (DHODB) from Lactococcus lactis is a heterotetramer containing two subunits of the protein encoded by the pyrDb gene (PyrDB) and two subunits of the protein encoded by the pyrK gene (PyrK). In addition, DHODB contains two molecules of flavin mononucleotide, two molecules of flavin adenine dinucleotide and two [2Fe-2S] iron-sulfur clusters as tightly bound cofactors. Yellow crystals of this enzyme have been grown using the hanging-drop vapour-diffusion technique from solutions of 2.5 M ammonium sulfate and 0.1 M sodium acetate, pH 4.6. The crystals have been shown to contain both the PyrDB and the PyrK subunits and fluorescence measurements indicate that the two different subunits interact very closely with each other in the active-site region. Native data sets have been collected to 2.6 A with a conventional X-ray source and to 2.2 A using synchrotron radiation. The crystals are rhombohedral, space group R32, with correspondin8 hexagonal unit-cell dimensions a = b = 202.3 and c = 81.0 A. The asymmetric unit in the crystal contains one PyrDB subunit and one PyrK subunit, which suggests that the two halves of the heterotetramer are related by a crystallographic twofold axis.

Journal Article↗
PubMed1997

[Potentially avoidable perinatal deaths in Denmark and Sweden 1991].

In 1991 the perinatal mortality rate in Denmark was 8.0/1000 deliveries compared to 6.5/1000 in Sweden. An international audit was designed to investigate whether the perinatal death rates in the two countries to some extent could reflect differences in the quality of care. Medical records of 97% of all perinatal deaths in 1991 in the two countries were analyzed. A new classification focusing on potential avoidability from a health services perspective was elaborated at a Nordic-Baltic workshop, using the variables: time of death in relation to admission and delivery, fetal malformation, gestational age, growth-retardation and Apgar score at 5 min. Rates of perinatal deaths of malformed infants (0.00195 and 0.00145) and intrapartum deaths of non-malformed infants (0.00042 and 0.00019) were significantly higher in Denmark than in Sweden. The study raised the following questions: why is the rate of perinatal death of malformed infants higher in Denmark than in Sweden and could intrapartum care in Denmark be improved?

Apgar Score↗
PubMed1997

A randomized trial of enhanced therapy for early syphilis in patients with and without human immunodeficiency virus infection. The Syphilis and HIV Study Group.

BACKGROUND: Reports of neurosyphilis and invasion of cerebrospinal fluid by Treponema pallidum in patients with human immunodeficiency virus (HIV) infection have led to doubts about the adequacy of the recommended penicillin G benzathine therapy for early syphilis. METHODS: In a multicenter, randomized, double-blind trial, we assessed two treatments for early syphilis: 2.4 million units of penicillin G benzathine and that therapy enhanced with a 10-day course of amoxicillin and probenecid. The serologic and clinical responses of patients with and without HIV infection were studied during one year of follow-up. RESULTS: From 1991 through 1994, 541 patients were enrolled, including 101 patients (19 percent) who had HIV infection but differed little from the uninfected patients in their clinical presentations. The rates at which chancres and rashes resolved did not differ significantly according to treatment assignment or HIV status. Serologically defined treatment failures were more common among the HIV-infected patients. The single clinically defined treatment failure was in an HIV-infected patient. Rates of serologically defined treatment failure did not differ according to treatment group (18 percent at six months with usual therapy; 17 percent with enhanced therapy). T. pallidum was found at enrollment in the cerebrospinal fluid of 32 of 131 patients (24 percent) and after therapy in 7 of 35 patients tested. None had clinically evident neurosyphilis, and the rate of detection of T. pallidum did not differ according to HIV status. CONCLUSIONS: After treatment for primary or secondary syphilis, the HIV-infected patients responded less well serologically than the patients without HIV infection, but clinically defined failure was uncommon in both groups. Enhanced treatment with amoxicillin and probenecid did not improve the outcomes. Although T. pallidum was detected in cerebrospinal fluid before therapy in a quarter of the patients tested, such a finding did not predict treatment failure. The current recommendations for treating early syphilis appear adequate for most patients, whether or not they have HIV infection.

Adult↗
PubMed1997

The crystal structure of rhamnogalacturonase A from Aspergillus aculeatus: a right-handed parallel beta helix.

BACKGROUND: Pectic substances are the major polysaccharide components of the middle lamella and primary cell wall of dicotyledonous plants. They consist of homogalacturonan 'smooth' regions and highly rhamnified 'hairy' regions of rhamnogalacturonan. The backbone in rhamnogalacturonan-l (RG-l), which is composed of alternating galacturonic acid and rhamnose residues, is the substrate for a new class of enzymes known as rhamnogalacturnoases (RGases). RGase A is a novel enzyme implicated in the enzymatic degradation of RG-l. RESULTS: The structure of RGase A from Aspergillus aculeatus has been solved by the single isomorphous replacement method including anomalous scattering (SIRAS method) to 2.0 A resolution. The enzyme folds into a large right-handed parallel beta helix, with a core composed of 13 turns of beta strands. Four parallel beta sheets (PB1, PB1a, PB2 and PB3), formed by the consecutive turns, are typically separated by a residue in the conformation of a left-handed alpha helix. As a consequence of the consecutive turns, 32% of all residues have their sidechains aligned at the surface or in the interior of the parallel beta helix. The aligned residues at the surface are dominated by threonine, aspartic acid and asparagine, whereas valine, leucine and isoleucine are most frequently found in the interior. A very large hydrophobic cavity is found in the interior of the parallel beta helix. The potential active site is a groove, oriented almost perpendicular to the helical axis, containing a cluster of three aspartic acid residues and one glutamic acid residue. The enzyme is highly glycosylated; two N-linked and eighteen O-linked glycosylation sites have been found in the structure. CONCLUSIONS: Rhamnogalacturonase A from A. aculeatus is the first three-dimensional structure of an enzyme hydrolyzing glycoside bonds within the backbone of RG-l. The large groove, which is the potential active site of RGase A, is also seen in the structures of pectate lyases. Two catalytic aspartic acid residues, which have been proposed to have a catalytic role, reside in this area of RGase A. The distance between the aspartic acid residues is consistent with the inverting mechanism of catalysis. The glycan groups bound to RGase A are important to the stability of the crystal, as the carbohydrate moiety is involved in most of the intermolecular hydrogen bonds.

Amino Acid Sequence↗
PubMed1997

[A time study in a department of histopathology].

In the Department of Histo- and Cytopathology, Herlev University Hospital, Copenhagen, a time study was performed according to the principles known from work sampling. From 22.11-12.12.1993 laboratory technicians, pathologists and secretaries were interviewed and an activity form was filled in. Six thousand nine hundred and fifty interviews were performed and the time study showed that for all groups of personnel 40% of the time was used on specimens sent for microscopy, 5% on autopsies (excl. microscopy), 15% on teaching and research, 20% on scientific meetings, reading and administration and 20% on other activities e.g. lunch, holiday, absence owing to illness. There was little variation for the different groups of personnel. On the other hand the time used on specific laboratory procedures, e.g. serial cutting, special-, and immunostaining, varied considerably for laboratory technicians, pathologists and secretaries respectively. Time studies, especially "work sampling" yield important information for the planning of laboratory services and provide documentation also for the time not directly related to routine work.

Denmark↗
PubMed1997

[The influence of dietary factors on weight change estimated by the use of multivariate graphical models].

The aim of the present study was to analyse the influence of dietary factors on weight change in a multifactorial context by use of graphical models. A random sample of 2304 Danish men and women, aged 30, 40, 50, and 60 years, living in Copenhagen County underwent a general health examination, and their BMI was calculated. They all completed questionnaires regarding education, life conditions, life habits, and dietary intake at entry. At follow-up five years later BMI was also calculated. BMI at entry depended on family predisposition to obesity, and for women, on cohabitation as well. At follow-up five years later BMI in the male group was only related to former BMI, whereas in the female group it was influenced by parity as well: No association was found between total energy intake, percentage of energy from fat or from alcohol and weight changes. No influence of other putative determining factors was found for either gender. We conclude, that although the graphical model detected several relations between diet, habits, and social factors, no influence of dietary factors on weight changes were found by use of multifactorial graphical models.

Adult↗
PubMed1997

Crystal structure of the dihaem cytochrome c4 from Pseudomonas stutzeri determined at 2.2A resolution.

BACKGROUND: . Cytochromes c4 are dihaem cytochromes c found in a variety of bacteria. They are assumed to take part in the electron-transport systems associated with both aerobic and anaerobic respiration. The cytochrome c4 proteins are located in the periplasm, predominantly bound to the inner membrane, and are able to transfer electrons between membrane-bound reduction systems and terminal oxidases. Alignment of cytochrome c4 sequences from three bacteria, Pseudomonas aeruginosa, Pseudomonas stutzeri and Azotobacter vinelandii, suggests that these dihaem proteins are composed of two similar domains. Two distinctly different redox potentials have been measured for the Ps. stutzeri cytochrome c4, however. RESULTS: . The crystal structure of the dihaem cytochrome c4 from Ps. stutzeri has been determined to 2.2A resolution by isomorphous replacement. The model, consisting of two entire cytochrome c4 molecules and 138 water molecules in the asymmetric unit, was refined to an R value of 20.1% for all observations in the resolution range 8-2.2A. The molecule is organized in two cytochrome c-like domains that are related by a pseudo-twofold axis. The symmetry is virtually perfectly close to the twofold axis, which passes through a short hydrogen bond between the two haem propionic acid groups, connecting the redox centre of each domain. This haem-haem interaction is further stabilized by an extensive symmetrical hydrogen-bond network. The twofold symmetry is not present further away from the axis, however, and the cytochrome c4 molecule can be considered to be a dipole with charged residues unevenly distributed between the two domains. The haem environment in the two domains show pronounced differences, mainly on the methionine side of the haem group. CONCLUSIONS: . The structure, in conjunction with sequence alignment, suggests that the cytochrome protein has evolved by duplication of a cytochrome c gene. The difference in charge distribution around each haem group in the two domains allows the haem group in the N-terminal domain to be associated with the lower redox potential of 241 mV and the C-terminal haem group with the higher potential of 328 mV. The molecular dipole characteristic of cytochrome c4 is important for its interaction with, and recognition of, its redox partners. In cytochrome c4, the hydrogen-bond network (between residues that are conserved in all known cytochrome c4 subspecies) seems to provide an efficient pathway for an intramolecular electron transfer that can ensure cooperativity between the two redox centres. The C-pyrrole corners of the haem edges are potential sites for external electron exchange.

Amino Acid Sequence↗
PubMed1997

The crystal structure of the flavin containing enzyme dihydroorotate dehydrogenase A from Lactococcus lactis.

BACKGROUND: . Dihydroorotate dehydrogenase (DHOD) is a flavin mononucleotide containing enzyme, which catalyzes the oxidation of (S)-dihydroorotate to orotate, the fourth step in the de novo biosynthesis of pyrimidine nucleotides. Lactococcus lactis contains two genes encoding different functional DHODs whose sequences are only 30% identical. One of these enzymes, DHODA, is a highly efficient dimer, while the other, DHODB, shows optimal activity only in the presence of an iron-sulphur cluster containing protein with which it forms a complex tetramer. Sequence alignments have identified three different families among the DHODs: the two L. lactis enzymes belong to two of the families, whereas the enzyme from E. coli is a representative of the third. As no three-dimensional structures of DHODs are currently available, we set out to determine the crystal structure of DHODA from L. lactis. The differences between the two L. lactis enzymes make them particularly interesting for studying flavoprotein redox reactions and for identifying the differences between the enzyme families. RESULTS: . The crystal structure of DHODA has been determined to 2.0 resolution. The enzyme is a dimer of two crystallographically independent molecules related by a non-crystallographic twofold axis. The protein folds into and alpha/beta barrel with the flavin molecule sitting between the top of the barrel and a subdomain formed by several barrel inserts. Above the flavin isoalloxazine ring there is a small water filled cavity, completely buried beneath the protein surface and surrounded by many conserved residues. This cavity is proposed as the substrate-binding site. CONCLUSIONS: . The crystal structure has allowed the function of many of the conserved residues in DHODs to be identified: many of these are associated with binding the flavin group. Important differences were identified in some of the active-site residues which vary across the distinct DHOD families, implying significant mechanistic differences. The substrate cavity, although buried, is located beneath a highly conserved loop which is much less ordered than the rest of the protein and may be important in giving access to the cavity. The location of the conserved residues surrounding this cavity suggests the potential orientation of the substrate.

Amino Acid Sequence↗
PubMed1997

Crystallization and preliminary X-ray studies of rhamnogalacturonase A from Aspergillus aculeatus.

Recombinant rhamnogalacturonase A from Aspergillus aculeatus has been crystallized and X-ray diffraction data has been collected. Crystals were grown by the hanging-drop vapour-diffusion technique, under the conditions 10% PEG 8000, 0.05 M KH(2)PO(4) and 0.1 M sodium acetate buffered at pH 3.5. The crystals diffract beyond 2.0 A resolution and belong to one of the orthorhombic space groups I2(1)2(1)2(1) or I222, with the unit-cell parameters a = 62.9, b = 125.4 and c = 137.0 A. There is one molecule in the asymmetric unit and a solvent content of approximately 54%. The enzyme is highly glycosylated corresponding to 5.9 kDa.

Journal Article↗
PubMed1997

The pharmacokinetics of tiagabine in healthy elderly volunteers and elderly patients with epilepsy.

The pharmacokinetics of tiagabine after single-dose (8 mg) and multiple-dose (3 mg, three-times daily for four days) administration of tiagabine HCl were investigated in healthy elderly volunteers (n = 8; Group 1), elderly patients with epilepsy receiving at least one hepatic enzyme-inducing antiepileptic drug (AED) (n = 8; Group 2), and healthy young volunteers (n = 8; Group 3). Participants were matched by gender, age (Groups 1 and 2), alcohol intake, body weight, and whether they smoked tobacco. The pharmacokinetic parameters of tiagabine following single- and multiple-dose administration were similar in both healthy elderly and young volunteers except for a small but significant difference in the area under the concentration-time curve after multiple-doses (103 +/- 29 ng.hr/mL/mg in the elderly versus 72 +/- 20 ng.hr/mL/mg in younger participants). This is not expected to have any clinical relevance because of the large intersubject variability in this parameter. In contrast, and as expected, the pharmacokinetics of tiagabine were altered in the presence of enzyme-inducing antiepileptic drugs: Time to reach maximum plasma concentration, area under the concentration-time curve, and elimination half-lives were significantly lower (e.g. 39 +/- 13 ng.hr/mL/mg for AUC after multiple-dose) compared with corresponding values in the healthy volunteers. These findings suggest that adjusting the dose of tiagabine on the basis of the age of the patient is not necessary, although, irrespective of age, higher doses and/or more frequent administrations will be required in patients taking concomitant enzyme-inducing antiepileptic drugs.

Adult↗
PubMed1997

Postural load during VDU work: a comparison between various work postures.

The aim of this study was to compare the postural load during VDU work in the following work postures: (1) Supporting and not supporting the forearms on the table top, (2) Sitting and standing positions, and (3) Sightline to the centre of the screen at an angle of 15 degrees and 30 degrees below the horizontal. The muscle load from the upper part of musculus trapezius and from the lumbar part of musculus erector spinae (L3 level) was measured by electromyography (EMG). Postural angles of head, upper arm and back were measured by inclinometers. The load on m. trapezius when using the keyboard was significantly less in sitting with supported forearms compared to sitting and standing without forearm support. Further, the time and number of periods when the trapezius load was below 1% MVC was significantly greater with support versus no support. The load on the right erector spinae lumbalis was also significantly less and the time when the load was below 1% MVC was significantly longer in a sitting work position with support versus standing without support. In addition, when using a mouse supporting the forearms reduced the static trapezius load in sitting. The results from this study document clearly the importance of giving the operator the possibility of supporting the forearms on the table top.

Adult↗
PubMed1997

Intrapartum death of nonmalformed fetuses in Denmark and Sweden in 1991. A perinatal audit.

BACKGROUND: In 1991 the rate of intrapartum death of non-malformed fetuses was higher in Denmark than in Sweden (4.2 vs. 1.9 per 10,000, OR 2.24). However, it is not clear whether this difference reflects potentially avoidable cases and/or suboptimal care. MATERIAL AND METHODS: Short descriptions were made from medical records of all 50 intrapartum deaths in Denmark and Sweden in 1991. Ten obstetricians, two from each of the Nordic countries, reviewed the cases to determine whether (1) intra-uterine death might have occurred before admission, (2) surveillance and intervention were insufficient, (3) fetal death was potentially avoidable by improved obstetric care; and, if so, to suggest ways of improved health care. RESULTS: There was a statistically higher rate of insufficient care (surveillance and intervention) (high or less degree) in the Danish cases (66% vs. 55%). The proportion of potentially avoidable fetal deaths was also higher in Denmark (59% vs. 52%) although the difference was not statistically significant. CONCLUSION: The significantly higher rate of intrapartum death of non-malformed infants in 1991 in Denmark compared to Sweden might be reduced by improved intrapartum surveillance and interventions.

Adult↗
PubMed1997

Deficient gastric lipase secretion in pancreatic insufficiency.

BACKGROUND: Gastrin is an important stimulator of gastric lipase secretion in man. In advanced pancreatic insufficiency gastric lipases might compensate for the lack of pancreatic lipases, but the role of gastrin in such compensation remains to be evaluated. The aim of this study was to examine the effect of gastrin on the gastric lipase secretion in patients with pancreatic insufficiency. METHODS: Eight patients with pancreatic insufficiency secondary to alcohol abuse were studied, and six healthy subjects volunteered as controls for the study. All volunteers received identical doses of intravenous gastrin-17 (10, 30, and 60 pmol/kg/h). The gastric content was measured, using a nasogastric tube for aspiration, and the amount and activity of gastric lipase output were determined. Plasma concentrations of gastrin, secretin, and cholecystokinin were measured by radioimmunoassays. RESULTS: The increased plasma levels of gastrin were accompanied by a dose-dependent increase in the amount and activity of gastric lipase in controls, but in the patients the response was almost abolished. CONCLUSIONS: Gastrin in postprandial concentrations does not influence the secretion of gastric lipase in patients with pancreatic insufficiency due to chronic pancreatitis.

Adult↗
PubMed1997

Helicobacter pylori infection in patients with chronic pancreatitis and duodenal ulcer.

BACKGROUND: The prevalence of duodenal ulcer is high in patients with chronic pancreatitis. Patients with simple duodenal ulcer without chronic pancreatitis are mostly Helicobacter pylori-infected, and the prevalence of IgG seropositivity is > 95%. The prevalence of H. pylori infection in patients with chronic pancreatitis is not known. METHODS: IgG antibodies against H. pylori were measured in a cross-sectional survey of consecutive patients who had their exocrine pancreas function examined with a Lundh meal test in the period 1988-95 and in a control group of patients with simple duodenal ulcer. RESULTS: Twenty-seven per cent of the patients with chronic pancreatitis had duodenal ulcer during the observation period. The prevalence of IgG antibodies against H. pylori was 22% in patients with chronic pancreatitis without duodenal ulcer as compared with 27% with non-organic abdominal pain. The prevalence of IgG antibodies against H. pylori was 60% in patients with chronic pancreatitis complicated by duodenal ulcer as compared with 86% in controls with simple duodenal ulcer. CONCLUSIONS: H. pylori infection contributes but may not be the only cause of duodenal ulcer in patients with chronic pancreatitis.

Adult↗
PubMed1997

Randomized controlled trial with sequential design of laparoscopic versus conventional appendicectomy.

BACKGROUND: A prospective study including 272 patients with suspected appendicitis was performed. The aims were to evaluate the representativity of the study group and to compare diagnostic and therapeutic laparoscopy with conventional appendicectomy. METHODS: The study was an open, randomized, single-centre trial with sequential design. One hundred and eight patients were randomized between laparoscopy or conventional appendicectomy, of whom 84 had acute appendicitis. Duration of postoperative convalescence was the major endpoint. RESULTS: The study patients were representative of the eligible population regarding age and stage of appendicitis. The risk of unnecessary appendicectomy was significantly (P = 0.03) lower after laparoscopy. The mean difference in duration of postoperative convalescence was 4.7 days in favour of of laparoscopic appendicectomy (P = 0.07), and 26 min in duration of operation in favour of conventional appendicectomy (P < 0.01). No differences were detected in postoperative hospital stay, pain assessment or complications. CONCLUSION: The laparoscopic procedure is at least as good as conventional appendicectomy. Initial laparoscopy reduces the rate of misdiagnosis.

Adolescent↗