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Biomedical subjects

H Boer

Publications and source records attributed to H Boer.

At least 19 recordsLinked to original sources
PubMed2000

Characterization of Trichoderma reesei cellobiohydrolase Cel7A secreted from Pichia pastoris using two different promoters.

Heterologous expression of T. reesei cellobiohydrolase Cel7A in a methylotrophic yeast Pichia pastoris was tested both under the P. pastoris alcohol oxidase (AOX1) promoter and the glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter in a fermentor. Production of Cel7A with the AOX1 promoter gave a better yield, although part of the enzyme expressed was apparently not correctly folded. Cel7A expressed in P. pastoris is overglycosylated at its N-glycosylation sites as compared to the native T. reesei protein, but less extensive than Cel7A expressed in Saccharomyces cerevisiae. The k(cat) and K(m) values for the purified protein on soluble substrates are similar to the values found for the native Trichoderma Cel7A, whereas the degradation rate on crystalline substrate (BMCC) is somewhat reduced. The measured pH optimum also closely resembles that of purified T. reesei Cel7A. Furthermore, the hyperglycosylation does not affect the thermostability of the enzyme monitored with tryptophane fluorescence and activity measurements. On the other hand, CD measurements indicate that the formation of disulfide bridges is an important step in the correct folding of Cel7A and might explain the difficulties encountered in heterologous expression of T. reesei Cel7A. The constitutive GAP promoter expression system of P. pastoris is nevertheless well suited for activity screening of cellulase activities in microtiter plates. With this type of screening method a faster selection of site-directed and random mutants with, for instance, an altered optimum pH is possible, in contrast to the homologous T. reesei expression system.

Biotechnology↗
PubMed2000

Duration of regrowth of ryegrass (Lolium perenne) effects on grazing behavior, intake, rumen fill, and fermentation of lactating dairy cows.

The relative importance of duration of sward regrowth and fill and fermentation in the rumen on the control of grazing time and intake rate during the first grazing session of the day was studied. Four lactating dairy cows were allowed to graze ryegrass (Lolium perenne) swards, with five different regrowth periods after mowing (6, 9, 16, 22, and 30 d). The cows were allowed to graze until they stopped voluntarily (cessation of grazing activity for at least 15 min). Before and after grazing the rumen contents were evacuated, weighed, sampled, and returned to the animals. Samples of rumen liquid were taken immediately before rumen evacuation and approximately 30, 60, 120, and 240 min after the grazing session was finished. Grazing time and intake rate did not follow a significant trend with period of regrowth. Bite rate did not change significantly with duration of regrowth with cows exhibiting high rates of biting for all the sward conditions. Rumen pools sizes of dry matter, neutral detergent fiber, and volatile fatty acids (VFA), measured after grazing, increased significantly with days of sward regrowth, even though the changes over days were small. Concentration of VFA followed a significant quadratic trend with a maximum concentration observed at approximately 110 min after cessation of grazing. In this study, rumen fill, VFA (either total or major components), ammonia, pH, and osmotic pressure as individual variables were not correlated with grazing time or dry matter intake.

Animals↗
PubMed1998

The thermal stability and domain interactions of the mannitol permease of Escherichia coli. A differential scanning calorimetry study.

The thermal stability and domain interactions in the mannitol transporter from Escherichia coli, enzyme IImtl, have been studied by differential scanning calorimetry. To this end, the wild type enzyme, IICBAmtl, as well as IICBmtl and IICmtl, were reconstituted into a dimyristoylphosphatidylcholine lipid bilayer. The changes in the gel to liquid crystalline transition of the lipid indicated that the protein was inserted into the membrane, disturbing a total of approximately 40 lipid molecules/protein molecule. The thermal unfolding profile of EIImtl exhibited three separate transitions, two of which were overlapping, that could be assigned to structural domains in the protein. Treatment with trypsin, resulting in the degradation of the water-soluble part of the enzyme while leaving the binding and translocation capability of the enzyme intact, resulted in a decrease of the Tm and enthalpy of unfolding of the membrane-embedded C domain. This effect was much more apparent in the presence of the substrate but only partly so in the presence of the substrate analog perseitol. These results are consistent with a recently proposed model (Meijberg, W., Schuurman-Wolters, G. K., and Robillard, G. T. (1998) J. Biol. Chem. 273, 7949-7946), in which the B domain takes part in the conformational changes during the substrate binding process.

Base Sequence↗
PubMed1998

Prader-Willi syndrome and psychotic symptoms: 1. Case descriptions and genetic studies.

Six people with Prader-Willi syndrome (PWS) who developed psychoses are described. Along with other literature reviewed in the present paper, the results imply an association between PWS and psychotic symptoms. Genetic studies were possible in five cases and SNRPN expression was examined in three cases. Maternal uniparental disomy and 15q11q13 deletions were found, demonstrating that psychotic symptoms are not associated with a single type of genetic abnormality.

Adolescent↗
PubMed1998

The use of cumulative gas and volatile fatty acid production to predict in vitro fermentation kinetics of Italian ryegrass leaf cell walls and contents at various time intervals.

Differences between the fermentation characteristics of cell contents (CC) and protease-treated cell walls (CW) of young leaves of Italian ryegrass (Lolium multiflorum Lam.) cultivar Multimo (tetraploid), were studied in vitro. Gas and volatile fatty acid (VFA) production rates were measured at regular intervals, as was the degradability of organic matter (OM) of CW. The measured VFA were used to predict the gas production and fermentable OM using stoichiometric calculations. For CW the volume and kinetics of measured gas production were the same as those predicted from the VFA formed. In contrast, the measured gas production for CC was consistently less than predicted, indicating that the stoichiometric equations were not valid for rapidly fermenting substrates. For both CC and CW, the relative rate of acetic acid production levelled off more slowly than for other VFA, resulting in an increasing gas yield (in ml/g fermentable OM) after 12 (CW)-24 (CC) h incubation. Consequently, the fermentation of OM was not linearly related to gas production kinetics. For CW, the kinetics of decline of degradable OM and fermentable OM were the same, after correction for a constant 'lost fraction' of degradable OM of 205 g/kg OM. This work indicates the value of detailed studies of fermentation processes to evaluate herbage quality. In particular, the role of CC and the difference between degradation and fermentation require further attention.

Cell Wall↗
PubMed1998

Medical opinions, beliefs and prescription of orthopaedic footwear: a survey of Dutch orthopaedists and rehabilitation practitioners.

OBJECTIVES: To get insight into medical opinions about the use of orthopaedic footwear and the medical and social factors related to the prescription of orthopaedic footwear by orthopaedists and rehabilitation practitioners. METHODS: In this study 85 orthopaedists and 96 rehabilitation practitioners filled out a questionnaire measuring perceived desirability of prescribing orthopaedic footwear in specific medical conditions, the perceived advantages of orthopaedic footwear, the perceived disadvantages of orthopaedic footwear, the attitude to orthopaedic footwear and satisfaction with the co-operation with the pedorthist. Clinicians were asked to estimate their referral rate of orthopaedic footwear. RESULTS: Orthopaedists and rehabilitation practitioners agree that the prescription of orthopaedic footwear should be considered in the case of rheumatoid arthritis, amputation of the foot and diabetic foot and not be considered in the case of sprain and back pain. In the case of hallux valgi, dermatological problems and clavus (severe corn) a reticent prescription policy seems to be the optimal choice. In the other medical conditions studied no unequivocal prescription policy could be derived. Respondents who prescribed orthopaedic footwear more than the median (more than 50 prescriptions per year) were more often rehabilitation practitioner, perceived more advantages of prescription footwear, perceived less disadvantages of prescription footwear and were more satisfied about the co-operation with the pedorthist. CONCLUSION: In some medical conditions orthopaedists and rehabilitation practitioners agree about the optimal use of orthopaedic footwear. In some other medical conditions orthopaedists and rehabilitation practitioners are divided about the use of orthopaedic footwear. Reported rate of prescription was not related to desirability of prescription, but was related to beliefs such as perceived advantages, perceived disadvantages and satisfaction with co-operation with the pedorthist, underlining the importance of cognitive factors in prescription style.

Adult↗
PubMed1998

Problem behaviors associated with deletion Prader-Willi, Smith-Magenis, and cri du chat syndromes.

Problem behaviors of individuals who had one of three chromosome deletion disorders (5p- cri-du-chat, 15q- Prader-Willi, or 17p- Smith-Magenis) were investigated. The Aberrant Behavior Checklist was used. Results were contrasted with those of two groups of people with mental retardation who were described in other studies. The checklist rates many, but not all, potentially relevant behaviors. Eating abnormalities, known to be problematic in Prader-Willi syndrome, and sleep abnormalities, believed to be problematic in Smith-Magenis syndrome, were not included in the survey. All three disorders were associated with greater ratings of problem behaviors than the comparison groups on at least one subscale of the checklist. The results lend support to the partial specificity model of behaviors associated with genetically determined syndromes.

Adolescent↗
PubMed1996

Relation between the oligomerization state and the transport and phosphorylation function of the Escherichia coli mannitol transport protein: interaction between mannitol-specific enzyme II monomers studied by complementation of inactive site-directed mutants.

Previous experiments with the mannitol-specific enzyme II of Escherichia coli, EIImtl, have demonstrated that (1) the enzyme is a dimer, (2) the dimer is necessary for maximum activity, and (3) phosphoryl groups could be transferred between EIImtl subunits [van Weeghel et al. (1991) Biochemistry 30, 1768-1773; Weng et al. (1992) J. Biol. Chem. 267, 19529-19535; Weng & Jacobson (1993) Biochemistry 32, 11211-11216; Stolz et al. (1993) J. Biol. Chem. 268, 27094-27099]. The experiments in this article address the mechanistic role of the dimer. They indicate that the A, B, and C domains of EIImtl preferentially interact within the same subunit. Site-directed mutants in each of the three domains of EIImtl were used to study phosphoryl group transfer by the EIImtl dimer in vitro and mannitol transport in vivo. The C domain mutant, EIImtl-G196D, which was unable to bind mannitol, and the separated C domain, IICmtl, which was unable to phosphorylate mannitol, formed a heterodimer which was capable of mannitol phosphorylation in vitro and mannitol transport in vivo. The rates of phosphorylation were approximately 10-fold lower in heterodimers containing two inactive subunits relative to the rates in heterodimers containing one inactive and one wild type subunit; phosphoryl group transfer through one subunit is kinetically preferred to intersubunit transfer. Heterodimers formed in vivo between one wild type EIImtl subunit and the CB domain double mutant, EIImtl-G196D/C384S, transported mannitol as rapidly as wild type EIImtl alone; the presence of the inactive double mutant subunit did not reduce the transport rate. Thus, only one active A, B, and C domain in the dimer is sufficient for transport and phosphorylation activity, and if all three domains are situated on the same subunit, maximum rates are achieved.

Biological Transport↗
PubMed1996

Health education to improve repeat participation in the Dutch breast cancer screening programme: evaluation of a leaflet tailored to previous participants.

Participation in breast cancer screening programmes often declines in the course of the programme. The purpose of the present study was to examine whether health education could diminish the amount of drop-outs between two screening rounds. The health education was tailored to women who previously underwent mammography. Based on the Elaboration Likelihood Model two versions of the tailored leaflet were made: a simple version and a version with additional peripheral cues. In an experimental study among 2961 women the effects of the tailored leaflets on reparticipation were tested against a standard leaflet. Re-participation rates were high (> 90%) and did not differ between the 3 groups. No significant differences regarding beliefs about re-participating were found between the 3 groups. Results indicate that the tailored information leaflets did not enhance re-participation. Therefore, the required additional efforts and costs do not seem to be justified. The results of the study provide indications that less painful mammograms and friendly staff might improve re-participation.

Aged↗
PubMed1996

Maladaptive behaviour in Prader-Willi syndrome in adult life.

Thirty adults with Prader-Willi syndrome (PWS) were compared with 30 adults with non-specific learning disability matched for age, sex and severity of mental retardation. Maladaptive behaviour was assessed with the Aberrant Behavior Checklist (ABC), a 58-item structured interview which rates behaviours from 0 (not a problem) to 3 (severe problem) and which yields five factors (I) irritability, agitation; (II) lethargy, withdrawal; (III) stereotypic behavior; (IV) hyperactivity, non-compliance; and (V) inappropriate speech). The PWS sample had significantly higher factor I (P < 0.001) and factor V (P < 0.05) scores. The PWS sample had mean scores above 1 for 17 ABC items; the contrast subjects had no mean scores above 1. The factor I scores for the PWS sample were similar to those of inpatients in hospital facilities for adults with mental retardation and mental illness or severely challenging behaviour. The results support previous work, and extend it by suggesting that temper tantrums, self-injury, impulsiveness, lability of mood, inactivity and repetitive speech are characteristic behaviours in PWS in adult life. Studies of the reasons for heterogeneity in behaviour are now needed.

Activities of Daily Living↗
PubMed1996

Perceived risk, anxiety, mammogram uptake, and breast self-examination of women with a family history of breast cancer: the role of knowing to be at increased risk.

Since women with a first-degree relative with breast cancer are at increased risk for breast cancer, it is of special importance that they adhere to early detection programs. In this study, women with (389) and without (3295) a family history of breast cancer were compared with respect to risk perception, breast cancer anxiety, and early detection behavior. Special attention was paid to the role of knowing that family history is a breast cancer risk factor. It was found that 46% of "family history positives" did not know that their risk was increased by their family history. Still, family history positives had increased risk perception; our results suggest that this was partly caused by their knowing they belonged to a risk group and partly by their having experienced the disease at close range. Although family history positives had higher risk perceptions, no differences in early detection behavior were found. This could not be attributed to high anxiety levels. Implications for health education are discussed.

Anxiety↗
PubMed1995

Phosphorylation site mutants of the mannitol transport protein enzyme IImtl of Escherichia coli: studies on the interaction between the mannitol translocating C-domain and the phosphorylation site on the energy-coupling B-domain.

Mannitol binding and translocation catalyzed by the C domain of the Escherichia coli mannitol transport protein enzyme IImtl is influenced by domain B. This interaction was studied by monitoring the effects of mutating the B domain phosphorylation site, C384, on the kinetics of mannitol binding to the C domain. The dissociation constants for mannitol to the C384 mutants in inside-out membrane vesicles varied from 45 nM for the wild-type enzyme to 306 nM for the mutants. The rate constants pertinent to the binding equilibrium were also altered by the mutations. The association rate of mannitol to the cytoplasmic binding site in the mutants was accelerated for all mutants. The exchange rate of bound mannitol on the wild-type enzyme was shown to be pH dependent with a pKa of approximately 8 and increasing rates at higher pH. This rate was increased for all the mutants, but the pKas differed for the various mutants. The exchange rate for binding to the isolated IICmtl, however, was not pH dependent and exhibited a low rate. Exchange measured at 4 degrees C showed that, of the two steps, binding and occlusion, involved in binding to wild-type EIImtl in inside-out vesicles, only one could be detected for the C384E and C384L mutants. This suggests that the mutations increased the rate of the occlusion step so that it was no longer separable from the initial binding step or that the mutations eliminated the occlusion step altogether. The change in the mannitol binding kinetics of the C domain indicates that the B and C domains of EIImtl influence each other's conformation.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1994

Expression, purification, and kinetic characterization of the mannitol transport domain of the phosphoenolpyruvate-dependent mannitol phosphotransferase system of Escherichia coli. Kinetic evidence that the E. coli mannitol transport protein is a functional dimer.

The overexpression of the membrane-bound C domain of the mannitol transport protein EIIMtl of Escherichia coli has been achieved. This protein, IICMtl, consisting of the first 346 amino acids, was purified from membrane vesicles and still bound mannitol with a high affinity. Gel filtration experiments showed that purified IICMtl was a dimer, confirming that the interaction within the EIIMtl dimer occurs between the membrane-bound portions of the protein. IICMtl in combination with a chimeric protein consisting of the membrane-bound EIIGlc C domain and the cytoplasmic EIIMtl BA domain could restore both phosphoenolpyruvate-dependent phosphorylation and mannitol/mannitol-P exchange activity. The interaction in this complex was comparable to that of IICMtl with soluble IIBAMtl in as much as there appeared to be no specific interaction between IICMtl and the membrane-bound EIIGlc C domain; the Km of IICMtl for the chimer was so low that saturation could not be achieved. In contrast, a very high affinity with a Km of 2 nM was measured between purified IICMtl and purified EIIMtl. This interaction was manifested in a IICMtl-dependent stimulation of the EIIMtl catalyzed phosphoenolpyruvate-dependent mannitol phosphorylation reaction and the mannitol/mannitol-P exchange reaction. The high affinity of IICMtl for the wild type enzyme can be explained by the formation of heterodimers consisting of a IICMtl monomer and an EIIMtl monomer which interact at the level of the membrane-bound domains. The 2-fold increase in mannitol phosphorylation activity of the hetero- versus homodimer is an indication that the individual subunits in the homodimer are functionally coupled and work at only half their maximum rate. It is known that the EIIMtl dimer, but not the monomer, catalyzes the mannitol/mannitol-P exchange reaction. Since the heterodimer also catalyzes this reaction, it appears that only one functional B domain is required per dimer.

Base Sequence↗
PubMed1993

Expression and characterization of a structural and functional domain of the mannitol-specific transport protein involved in the coupling of mannitol transport and phosphorylation in the phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli.

The mannitol-specific transport protein in Escherichia coli, EIImtl, consists of three structural and functional domains: a hydrophilic EIII-like domain (the A domain); a hydrophobic transmembrane domain (the C domain); and a second hydrophilic domain (the B domain) which connects the A and C domains together. The A domain contains the first phosphorylation site, His554, while the B domain contains the second phosphorylation site, Cys384. The phosphoryl group which is needed for the active transport of mannitol is sequentially transferred from P-enolpyruvate via the two phosphorylation sites to mannitol bound to the substrate binding site. In this paper, the expression, purification, and initial characterization of the B domain, IIBmtl, are described. Oligonucleotide-directed mutagenesis was used to produce an amber stop codon (TAG) and HindIII restriction site in a flexible loop between the B and A domains in the subcloned gene fragment coding for IIBAmtl (van Weeghel et al., 1991c). The gene fragment coding for IIBmtl was then subcloned behind strong promoters, located in two different expression/mutagenesis vectors, which directed the expression of the 15.3-kDa polypeptide in Escherichia coli. The domain was purified from E. coli crude cell extracts by using Q-Sepharose Fast Flow, S-Sepharose Fast Flow, and hydroxylapatite column steps. This purification procedure resulted in 1 mg of pure IIBmtl/g of cell, wet weight. The purified B domain was analyzed in vitro for its catalytic activity with membranes containing the phosphorylation site mutant form of EIImtl, C384S, and with the transmembrane domain, IICmtl. The B domain, together with purified IIA, was able to restore the P-enolpyruvate-dependent phosphorylation activity of the membrane-bound C domain. Steady-state mannitol phosphorylation kinetics at saturating EI, HPr, and IIAmtl yielded an apparent Km of P-IIBmtl for IICmtl of 200 microM and an apparent Vmax of 71 nmol of mtl-P min-1 mg of membrane protein)-1. This Vmax value is comparable to that of wild-type EIImtl measured under the same experimental conditions.

Base Sequence↗
PubMed1993

Absorption of volatile fatty acids from the rumen of lactating dairy cows as influenced by volatile fatty acid concentration, pH and rumen liquid volume.

The effect of rumen liquid volume, pH and concentration of volatile fatty acids (VFA) on the rates of absorption of acetic, propionic and butyric acids from the rumen was examined in lactating dairy cows. Experimental solutions introduced into the emptied, washed rumen comprised two different volumes (10 or 30 l), four levels of pH (4.5, 5.4, 6.3, 7.2) and three levels of individual VFA concentrations (20, 50 or 100 mM-acetic, propionic or butyric acid). All solutions contained a total of 170 mM-VFA and an osmotic value of 400 mOsmol/l. Absorption rates were calculated from the disappearance of VFA from the rumen corrected for passage with liquid phase to the omasum. An increase in initial fluid pH caused a reduction in fractional absorption rates of propionic and butyric acids. Increasing the initial pH from 4.5 to 7.2 reduced fractional absorption rates of acetic, propionic and butyric acids from 0.35, 0.67 and 0.85 to 0.21, 0.35 and 0.28/h respectively. The fractional absorption rates of all VFA were reduced (P < 0.05) by an increase in initial rumen volume. The fractional absorption rate of acetic acid was lower (P < 0.05) at an initial concentration of 20 mM than of 50 mM. The fractional absorption rate of propionic acid tended (P < 0.10) to decrease as the level of concentration increased while fractional absorption rate of butyric acid was not affected by butyric acid concentration. These results indicate that relative concentrations of VFA in rumen fluid might not represent relative production rates and that attempts to estimate individual VFA production from substrate digestion must take account of pH and VFA concentration.

Acetates↗