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J van den Heuvel

Publications and source records attributed to J van den Heuvel.

17 recordsLinked to original sources
PubMed2004

Optimised fermentation strategy for 13C/15N recombinant protein labelling in Escherichia coli for NMR-structure analysis.

A widely applicable cultivation strategy, which reduces the costs of expensive isotopes, is designed for maximal (98-100%) incorporation of [13C] and [15N] into labelled recombinant protein expressed in Escherichia coli, allowing better assignment of the resonances for NMR studies. Isotope labelling of the culture was performed throughout the complete process, starting from preculture. Sufficient biomass is first generated in a batch phase. Upon consumption of glucose, identified by a sharp drop of on-line monitored oxygen consumption, expression is induced and cultivation is continued under glucose-limited conditions as fed-batch process. Thereby a quantitative utilisation of the most expensive component [13C]-glucose is achieved, while the approximate amount of the [15N]-ammonium chloride to be incorporated is calculated from the scheduled biomass. The usefulness of the strategy is demonstrated with production of uniformly [13C/15N]-labelled tryparedoxin of Crithidia fasciculata. Ideal isotope incorporation and product quality is documented by MALDI-TOF mass spectrometry and two- and three-dimensional NMR spectra.

Carbon Isotopes↗
PubMed2000

Nonnutritive sucking during heelstick procedures decreases behavioral distress in the newborn infant.

We investigated if nonnutritive sucking (NNS) during heelstick procedures alleviates behavioral distress in neonates. In our NICU, 26 neonates without severe complications (mean Minde score 0.8, range 0-3), undergoing heelstick procedures at least twice a day, in the first 2 weeks of life, were enrolled in the trial (mean gestational age 33.9 weeks, range 26-39 weeks, mean birth weight 1, 988.5 g, range 1,200-4,010 g, mean Apgar score at the first minute 6. 7, range 4-10, at the fifth minute 8.5, range 6-10). Two heelpricks were performed in each neonate with NNS randomly assigned. Behavioral states, transcutaneous oxygen tension (TcPO(2)), heart rate, and respiratory rate were monitored before, during and after the heelstick procedures. Heelstick procedures lasted for a mean of 109 s (range 50-230 s) with NNS, and a mean of 128.8 s (range 20-420 s) without NNS. Compared with baseline, heart rate and behavioral distress increased and respiratory rate decreased during heelstick and after heelstick. Oxygen tension did not change. Nonnutritive sucking had no effect on respiratory rate or transcutaneous oxygen tension, but reduced the time of crying and the heart rate increase during the procedure. In conclusion, NNS can be recommended to reduce distress in newborns undergoing invasive routine procedures. Further studies are needed to evaluate the effects of NNS on respiratory rate and blood gas levels.

Blood Specimen Collection↗
PubMed1998

Susceptibility towards intramolecular disulphide-bond formation affects conformational stability and folding of human basic fibroblast growth factor.

The conformational stability and the folding properties of the all-beta-type protein human basic fibroblast growth factor (hFGF-2) were studied by means of fluorescence spectroscopy. The results show that the instability of the biological activity of hFGF-2 is also reflected in a low conformational stability of the molecule. The reversibility of the unfolding and refolding process was established under reducing conditions. Determination of the free-energy of unfolding in the presence of reducing agents revealed that the conformational stability of hFGF-2 (DeltaGH2Oapp congruent with21 kJ. mol-1, 25 degreesC) is low compared with other globular proteins under physiological conditions (20-60 kJ.mol-1). However, the conformational stability of hFGF-2 is particularly low under non-reducing conditions. This instability is attributed to intramolecular disulphide-bond formation, rendering the molecule more susceptible to denaturant-induced unfolding. In addition, denaturant-induced unfolding of hFGF-2 renders the protein more susceptible to irreversible oxidative denaturation. Experimental evidence is provided that the irreversibility of the unfolding and refolding process in the absence of reducing agents is linked to the formation of an intramolecular disulphide bond involving cysteines 96 and 101.

3T3 Cells↗
PubMed1998

The genome-linked protein (VPg) of southern bean mosaic virus is encoded by the ORF2.

The sequence of the 20 N-terminal amino acids of the viral protein (VPg) which is covalently attached to the genomic RNA of the bean strain of Southern bean mosaic virus (SBMV-B) has been determined. The obtained VPg sequence mapped to position 327 to 346 of the SBMV-B ORF2 product, downstream of the putative protease domain and in front of the RNA-dependent RNA polymerase. Thus indicating that the sobemovirus genomic arrangement is similar to that of subgroup II luteoviruses. Comparison with other viral sequences revealed a high similarity with the sequence of the ORF2-product of the cowpea strain of SBMV (SBMV-C). No significant similarities were detected with amino acid sequences derived of other sobemoviruses or non-related viruses.

Amino Acid Sequence↗
PubMed1998

Probing the presumed catalytic triad of a selenium-containing peroxidase by mutational analysis.

Glutathione peroxidases (GPx) are characterized by a catalytically active selenium which forms the center of a strictly conserved triad composed of selenocysteine, glutamine, and tryptophan. In order to check the functional relevance of this structural peculiarity, six molecular mutants of phospholipid hydroperoxide glutathione peroxidase (PHGPx) were designed, isolated, and investigated kinetically. Replacement of the selenocysteine in position 46 by cysteine decreased k + 1, i.e., the reaction rate of reduced enzyme with hydroperoxide, by three orders of magnitude. The rate of regeneration of the reduced enzyme by glutathione (k' + 2) was similarly affected. Additional substitution of Gln81 or Trp136 by acid residues resulted in a further decrease of k + 1 by three orders of magnitude, whereas histidine or neutral residues in these positions proved to be less deleterious. The data support the hypothesis that the typical triad of selenocysteine, glutamine, and tryptophan is indeed a novel catalytic center in which the reactivity of selenium is optimized by hydrogen bonding provided by the adjacent glutamine and tryptophan residues.

Animals↗
PubMed1997

Expression of the potato leafroll virus ORF0 induces viral-disease-like symptoms in transgenic potato plants.

The role of the open reading frame 0 (ORF0) of luteoviruses in the viral infection cycle has not been resolved, although the translation product (p28) of this ORF has been suggested to play a role in host recognition. To investigate the function of the potato leafroll luteovirus (PLRV) p28 protein, transgenic potato plants were produced containing the ORF0. In the lines in which the ORF0 transcripts could be detected by Northern (RNA) analysis, the plants displayed an altered phenotype resembling virus-infected plants. A positive correlation was observed between levels of accumulation of the transgenic transcripts and severity of the phenotypic aberrations observed. In contrast, potato plants transformed with a modified, untranslatable ORF0 sequence were phenotypically indistinguishable from wild-type control plants. These results suggest that the p28 protein is involved in viral symptom expression. Southern blot analysis showed that the transgenic plants that accumulated low levels of ORF0 transcripts detectable only by reverse transcription-polymerase chain reaction, contained methylated ORF0 DNA sequences, indicating down-regulation of the transgene provoked by the putatively unfavorable effects p28 causes in the plant cell.

Amino Acid Sequence↗
PubMed1997

[Amalgam use and mercury emission in the Netherlands].

An overview is presented of the emission of mercury to the environment by restoring teeth with amalgam, extraction, replacement of amalgam, and the final phase of teeth. Important input data were the trade figures of amalgam. The emission of mercury from amalgam fillings are characterized by diffuse spreading. Many small sources are together a substantial source of the leakage of mercury to the environment. Amalgam adhering to cotton-wool and in extracted teeth deliver a relevant contribution to the mercury load in municipal waste. The total mercury emission from dental amalgam to the environment in the Netherlands is at the estimate 500 kg a year, with a worst case maximum of 935 kg.

Dental Amalgam↗
PubMed1996

Schizosaccharomyces pombe has a novel eukaryotic initiation factor 4F complex containing a cap-binding protein with the human eIF4E C-terminal motif KSGST.

Genetic and biochemical analyses were performed on the cytoplasmic cap-binding complex (eukaryotic initiation factor (eIF) 4F) of Schizosaccharomyces pombe. Genomic and cDNA sequencing of the S. pombe gene (tif1) encoding the cap-binding component eIF4E revealed the presence of two introns in a reading frame of 219 codons. The encoded sequence of 218 amino acids shows a greater degree of identity to the mammalian eIF4E sequence than does its counterpart from Saccharomyces cerevisiae. In particular, unlike its S. cerevisiae counterpart, S.pombe eIF4E has a C-terminal Ser209 within the motif KSGST that is a site of phosphorylation in hamster and rabbit eIF4E. Of relevance to its potential regulatory role, eIF4E was found to be encoded by an mRNA with a six-nucleotide leader and to be of low abundance in vivo. Cross-linking experiments identified S. pombe eIF4E as the major cap-binding protein while a further protein, p36, also showed cap-dependent binding. eIF4A was not associated with the cap-binding complex. While S. pombe eIF4E was shown capable of binding S. cerevisiae p20, an equivalent protein was absent from the eIF4F complex isolated from S. pombe cells. S. pombe 4F therefore shows a remarkable combination of structural and functional properties, some of which it shares with its higher and its lower eukaryotic counterparts.

Amino Acid Sequence↗
PubMed1996

[Supplementary selenium , an antidote against mercury?].

The consequences of both a high and a low intake of selenium are described in this article. Mercury released by dental silver amalgam might affect the protective functions of selenium. However, the literature does not sustain the existence of such an effect. In view of the small margin between safe and toxic doses of selenium and the absence of a scientific consensus as to the possible toxic effects of mercury from amalgam (additional to dietary mercury), it does not seem to be warranted to advise suppletion of selenium.

Antidotes↗
PubMed1996

[Selenium and mercury. (Un)healthy antagonism?].

The trace element selenium is involved in the protection against damage caused by free radicals. Selenium prevents carcinogenesis and growth of neoplasms. However, the mechanism is insufficiently known. Furthermore, selenium interacts with mercury, thereby preventing toxic reactions to high doses of mercury. The intake of selenium and the desired minimum and maximum concentrations are described.

Animals↗
PubMed1995

The highly acidic C-terminal region of the yeast initiation factor subunit 2 alpha (eIF-2 alpha) contains casein kinase phosphorylation sites and is essential for maintaining normal regulation of GCN4.

Regulation of the effective activity of eukaryotic initiation factor 2 (eIF-2) in protein synthesis is known to involve phosphorylation of its alpha subunit. Two mammalian enzymes, the haem-controlled repressor (HCR) and the double-stranded RNA-activated inhibitor (dsI), phosphorylate Ser-51 of the alpha subunit, thereby inhibiting the exchange of bound nucleotides on, and thus the recycling of, eIF-2. In Saccharomyces cerevisiae, the equivalent serine seems to be phosphorylated by the GCN2 protein kinase, which is activated by amino acid starvation. However, in the present paper we show that this is not the only site of phosphorylation in yeast eIF-2 alpha. We report the preparation of recombinant yeast eIF-2 alpha from Escherichia coli and its use in in vitro phosphorylation studies. Mammalian HCR and dsI are shown to phosphorylate specifically Ser-51 of yeast eIF-2 alpha, whereas extracts from yeast cells do not. Instead, at least one of three serine residue in the acidic C-terminal region of this protein is phosphorylated by fractions of yeast possessing casein kinase activities 1 and 2. A triple Ser-->Ala mutant form of yeast eIF-2 alpha was found to be no longer phosphorylated by either of the yeast (or mammalian) casein kinase activities in vitro. Isoelectric focusing of yeast extracts confirmed that the mutated sites normally act as sites of phosphorylation in vivo. The same mutant was used to show that the three sites have no essential function under normal physiological conditions in yeast. In contrast, deletion of the 13 amino acid long C-terminal region of eIF-2 alpha, including the three phosphorylation sites, led to derepression of GCN4 in vivo. Thus removal of the short, highly acidic C-terminal region of eIF-2 alpha has the same regulatory effect on translational (re)initiation as phosphorylation of the Ser-51 residue of the wild-type protein. This result provides new insight into the role of eIF-2 alpha activity in the regulation of translational (re-) initiation.

Amino Acid Sequence↗
PubMed1995

[The Dutch version of the McGill pain questionnaire: a reliable pain questionnaire].

OBJECTIVE: To assess whether the McGill pain questionnaire, translated into Dutch (MPQ-DLV), is a reliable instrument to measure pain. DESIGN: Questionnaire study. SETTING: Faculty of Social Sciences, University of Leiden, the Netherlands. METHOD: The MPQ-DLV was administered three times to 92 patients who had physiotherapy: in group I (n = 62) twice before and four hours after physiotherapy treatment, in group II (n = 30) before, directly after and four hours after treatment. The questionnaire consisted of questions to determine (a) the quality and intensity, (b) the localisation and evolution of the pain, (c) the effects of the pain on quality of life and further (d) visual analog pain intensity scales. Subsets of questions were combined into nine indices. For all indices on all three occasions Cronbach's alpha coefficients were determined. Moreover, test-retest correlation coefficients were determined between the scores of the first and second, the first and third, and the second and third occasions. RESULTS: The test-retest correlations of the nine indices and the visual analog pain intensity scales ranged from 0.62 to 0.93 (median: 0.84). Cronbach's alpha coefficients for the indices varied between 0.61 and 0.85 (median: 0.72). CONCLUSION: The MPQ-DLV is a reliable instrument for measuring pain.

Adolescent↗
PubMed1995

Probing the presumed catalytic triad of selenium-containing peroxidases by mutational analysis of phospholipid hydroperoxide glutathione peroxidase (PHGPx).

Single and double site mutants affecting the presumed catalytic centre of the selenoenzyme PHGPx were subjected to functional analysis. The rate constants k+1 and k'+2, for the oxidation and the regeneration of the ground state enzyme were estimated, respectively. Moreover, the alkylation rate of the reactive centre by iodoacetate (kinact.) was also analysed. The substitution of the catalytically competent selenocysteine 46 by cysteine (PHGPxcys46) decreased k+1 and k'+2 by about three orders of magnitude, although leaving unaffected kinact.. Furthermore, mutations of PHGPxcys46 involving the other residues of the triad decreased both kinact. and k+1, thus highlighting the involvement of Gln 81 and Trp 136 in the dissociation/activation of the nucleophilic cysteine thiol. In general, substitutions of Gln 81 or Trp 136 by acidic residues in PHGPxcys46 most dramatically depressed the k+1 values, because they practically prevented the dissociation of the thiol group, while neutral or positively charged residues in these positions allowed an intermediate dissociation and induced a corresponding reactivity of the thiol. Our data, for the first time, reveal that the presumed triad of selenocysteine, glutamine and tryptophan residues represents a novel type of catalytic centre, whose integrity is essential for the full catalytic function of glutathione peroxidases.

Animals↗
PubMed1994

Rubella embryopathy after maternal reinfection.

Reinfection with rubella is possible. The real risk for fetus and newborn is not known, as are the incidences of rubella reinfection during pregnancy and congenital rubella infection after maternal reinfection.

Antibodies, Viral↗
PubMed1990

GUUS an expert system in the intensive care unit.

In cooperation with the Rotterdam School of Management of the Erasmus University in Rotterdam, an expert system GUUS was developed in the intensive care unit of the Department of Thoracic Surgery of the Leiden University Hospital. This expert system is able to diagnose postoperative haemodynamic problems in patients after coronary artery surgery and can give suggestions for therapy. GUUS has been developed by using the expert system shell Acquaint. The knowledge base was initially based on existing protocols and interviews with the medical head of the intensive care unit. The first prototype was tested and modified by using actual patient cases collected via special questionnaires. Subsequently the performance of GUUS was tested in a single blind comparison with three human experts. The results of this test were encouraging and initiated further development and implementation of the system.

Artificial Intelligence↗
PubMedDate not supplied

Evaluation of fitting rules with a programmable hearing aid.

A study was performed with the 3M 8200 multi-programmable hearing aid in order to try to identify an optimal frequency-gain response, based on the standard calculation rules: NAL, POGO, Berger and Half gain. Furthermore, we examined to what extent multiple programs are used and appreciated. The 3M hearing aid was presented to 126 hearing-impaired patients for a trial period. The participants undertook several tests of speech intelligibility and sound quality. In comparison to the final settings after the trial period, it transpired that the NAL rule came f1p4est to the most used program and gave the best prediction of the gain at 1000 Hz. The attempt to optimize standard calculation rules according to indications made by the patients failed. The SRT-in-noise test showed improvements of the S/N ratio of 2.5 dB. The results of this study point towards separate processing of low- and high-frequency sounds as a useful concept.

Adult↗