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G Kroon

Publications and source records attributed to G Kroon.

9 recordsLinked to original sources
PubMed2003

Plasmodium vivax CS peptides display conformational preferences for folded forms in solution.

Spectroscopic techniques have been used to study the conformations of several synthetic peptides with sequences corresponding to the repeat regions of the circumsporozoite proteins of Plasmodium vivax, variants vk-210 and vk-247. As has previously been shown for P. falciparum, turn-like folded conformations are observed, in rapid dynamic equilibrium with extended-chain forms. These results are consistent with the known similarity of the structural, biosynthetic and immunological properties of the circumsporozoite proteins of different plasmodial species. Additionally, the observation of folded conformers provides a rationale for the effectiveness of these peptides as immunogens and potential vaccines.

Amino Acid Sequence↗
PubMed2001

Local structural plasticity of the prion protein. Analysis of NMR relaxation dynamics.

A template-assisted conformational change of the cellular prion protein (PrP(C)) from a predominantly helical structure to an amyloid-type structure with a higher proportion of beta-sheet is thought to be the causative factor in prion diseases. Since flexibility of the polypeptide is likely to contribute to the ability of PrP(C) to undergo the conformational change that leads to the infective state, we have undertaken a comprehensive examination of the dynamics of two recombinant Syrian hamster PrP fragments, PrP(29-231) and PrP(90-231), using (15)N NMR relaxation measurements. The molecular motions of these PrP fragments have been studied in solution using (15)N longitudinal (T(1)) and transverse relaxation (T(2)) measurements as well as [(1)H]-(15)N nuclear Overhauser effects (NOE). These data have been analyzed using both reduced spectral density mapping and the Lipari-Szabo model free formalism. The relaxation properties of the common regions of PrP(29-231) and PrP(90-231) are very similar; both have a relatively inflexible globular domain (residues 128-227) with a highly flexible and largely unstructured N-terminal domain. Residues 29-89 of PrP(29-231), which include the copper-binding octarepeat sequences, are also highly flexible. Analysis of the spectral densities at each residue indicates that even within the structured core of PrP(C), a markedly diverse range of motions is observed, consistent with the inherent plasticity of the protein. The central portions of helices B and C form a relatively rigid core, which is stabilized by the presence of an interhelix disulfide bond. Of the remainder of the globular domain, the parts that are not in direct contact with the rigid region, including helix A, are more flexible. Most significantly, slow conformational fluctuations on a millisecond to microsecond time scale are observed for the small beta-sheet. These results are consistent with the hypothesis that the infectious, scrapie form of the protein PrP(Sc) could contain a helical core consisting of helices B and C, similar in structure to the cellular form PrP(C). Our results indicate that residues 90-140, which are required for prion infectivity, are relatively flexible in PrP(C), consistent with a lowered thermodynamic barrier to a template-assisted conformational change to the infectious beta-sheet-rich scrapie isoform.

Animals↗
PubMed2000

Treatment of patients with long-standing unexplained subfertility with in vitro fertilization.

OBJECTIVE: To evaluate whether IVF is an effective treatment for long-standing unexplained subfertility. DESIGN: Retrospective cohort study. SETTING: Tertiary care infertility center in a university hospital. PATIENT(S): Two hundred two couples with unexplained subfertility of 2 years' duration or more who attended the center for their first IVF attempt. INTERVENTION(S): Couples were placed on a waiting list for IVF. They received no treatment until IVF was started. MAIN OUTCOME MEASURE(S): Pregnancy rate (PR) while on the waiting list and PR after IVF treatment. RESULT(S): Complete data sets were available for 131 couples. Seventeen of 131 women became pregnant while waiting for IVF treatment (PR 0.9% per exposure cycle), whereas 45 of 119 receiving IVF treatment became pregnant (PR 17% per IVF attempt). CONCLUSION(S): IVF treatment has substantial added value over waiting and is an efficient treatment for long-standing unexplained subfertility.

Adult↗
PubMed1993

Modified assay of prostate-specific antigen with a detection limit < 0.01 microgram/L.

We modified the Hybritech Tandem-E prostate-specific antigen (PSA) assay by increasing the sample volume, increasing enzyme-substrate incubation time, and using diethanolamine buffer. Our modified method has a detection limit of 0.009 microgram/L (P < 0.01). The assay curve is linear from 0.01 to 1.0 micrograms/L and has an overall assay time of about 4 h. Linear plots are obtained when the 1.0 micrograms/L standard is diluted with either matrix buffer or serum from men containing PSA < 0.01 microgram/L. Recovery of PSA (0.10 microgram/L) added to serum from men averaged 94%. Interassay CVs were 13%, 7%, and 4% at PSA concentrations of 0.04, 0.07, and 0.30 micrograms/L, respectively (n = 33). This assay should be useful in the detection of early recurrence of prostate cancer after radical prostatectomy.

Autoanalysis↗
PubMed1984

Automated calmagite compleximetric measurement of magnesium in serum, with sequential addition of EDTA to eliminate endogenous interference.

We describe an automated method for magnesium assay, for use with the Cobas-Bio centrifugal analyzer. Magnesium is reacted with calmagite, a dye, and the absorbance of the magnesium-dye complex at 520 nm is measured. EDTA is then added to break up the complex and the absorbance at 520 nm is re-measured to correct for sample color and turbidity. Including ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) and triethanolamine in the dye reagent eliminates interference by calcium and iron. Within-run CVs were less than 2.0% for concentrations of magnesium ranging from 18 to 40 mg/L, and less than 4% for a magnesium concentration of 9.4 mg/L. Day-to-day precision data, determined over five months were: mean = 21.0 mg/L, CV = 2.7%; mean = 43.0 mg/L, CV = 3.2% (n = 550 for both). Comparison of the Cobas-Bio method (y) with an atomic absorption spectrometric method (x) gave the following results: y = 0.968x + 0.448, r = 0.986, Sy/x = 0.34 mg/L, mean x = 19.8 mg/L, mean y = 19.6 mg/L, n = 44. Hemoglobin, bilirubin, and turbidity do not interfere. The standard curve is linear up to a magnesium concentration of 97 mg/L.

Autoanalysis↗
PubMed1981

Centrifugal analysis with automated sequential reagent addition: measurement of serum calcium.

We describe an automated method for calcium assay, for use with the Cobas-Bio centrifugal analyzer. Calcium is reacted with cresolphthalein complexone and the absorbance of the calcium--dye complex at 575 nm is measured. EDTA is then added to break up the calcium--dye complex and the absorbance at 575 nm is re-measured, to correct for endogenous color and turbidity. Day-to-day precision data, determined over four months, were as follows: mean = 92.9 mg/L, CV = 1.47%; n = 216; mean = 128.7 mg/L, CV = 1.72%; n = 216. Comparison of the Cobas-Bio method (y) with an atomic absorption spectrometric method (x) gave the following results: y = 1.012x--2.05, r = 0.991, Sy/x = 1.2, mean x = 92.63 mg/L, mean y = 91.69 mg/L, n = 74. Hemoglobin, bilirubin, or turbidity does not interfere. At the medical decision value (110 mg/L), the overall analytical error is 4.6 mg/L, which is less than the 5 mg/L allowable (95% confidence limit) error.

Autoanalysis↗
PubMedDate not supplied

Randomised controlled trial of magnetic-resonance pelvimetry in breech presentation at term.

BACKGROUND: Pelvimetry is widely used in women with breech presentation at term to select those for whom planned vaginal delivery is appropriate. However, its clinical value has never been established. We evaluated pelvimetry in a randomised controlled trial. The main outcome measures were the elective and emergency caesarean-section rates and the early condition of the neonate. METHODS: Magnetic-resonance (MR) pelvimetry was done on 235 women. The women were then randomly assigned to two groups--for the study group (n = 118), the pelvimetry results were reported to the responsible obstetricians, who used them as the basis for decisions on whether to schedule elective caesarean or trial of labour; for the control group (n = 117), the pelvimetry results were not disclosed until 8 weeks post partum, and decisions about obstetric management were made on the basis of clinical factors only. FINDINGS: 35 women (15 [13%] study group, 20 [17%] control group) had abnormalities on pelvimetry. The overall caesarean-section rates did not differ significantly between the study and control groups (50 [42%] vs 59 [50%], p = 0.24) but the emergency caesarean-section rate was significantly lower in the study group than in the control group (22 [19%] vs 41 [35%], p = 0.0052). The mean 1 min Apgar scores in the study and control groups were 8.1 and 8.0 (p = 0.93) and the mean 3 min scores 9.5 and 9.4, respectively (p = 0.28). There were no significant differences in the early neonatal outcome for infants born vaginally, by emergency caesarean section, or by elective caesarean section in the two groups, except for a significantly lower Apgar score in the six infants born vaginally to control-group women who had pelvic abnormalities. INTERPRETATION: The use of MR pelvimetry in breech presentation at term did not significantly reduce the overall caesarean-section rate. However, it allowed better selection of the delivery route, with a significantly lower emergency caesarean-section rate. Neonatal outcome was not compromised by use of the pelvimetry data.

Apgar Score↗