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K Dijkstra

Publications and source records attributed to K Dijkstra.

28 records · Page 2Linked to original sources
PubMed1992

Characterization of the protonation and hydrogen bonding state of the histidine residues in IIAmtl, a domain of the phosphoenolpyruvate-dependent mannitol-specific transport protein.

The A domain of the mannitol-specific EII, IIAmtl, was subcloned and proven to be functional in the isolated form (Van Weeghel et al., 1991). It contains a histidine phosphorylation site, the first of two phosphorylation sites in the parent protein. In this paper, we describe the characterization of the three histidine residues in IIAmtl with respect to their protonation and hydrogen bonding state, using 1H[15N] heteronuclear NMR techniques and protein selectively enriched with [delta 1,epsilon 2-15N]histidine. The active site residue has a low pKa (less than 5.8) and shows no hydrogen bond interactions. The proton in the neutral ring is located at the N epsilon 2 position, which also proved to be the site of phosphorylation. The phosphorylation raises the pKa of the active site histidine considerably but does not change the hydrogen bond situation. The other two histidine residues, one of which is probably located on the surface of the protein, were also characterized. Both show hydrogen bond interactions in the unphosphorylated protein, but these are disturbed by the phosphorylation process. These observations, combined with small changes in pKa and titration behavior, indicate that the IIAmtl changes its conformation upon phosphorylation.

Escherichia coli↗
PubMed1992

Three-dimensional 15N-1H-1H and 15N-13C-1H nuclear-magnetic resonance studies of HPr a central component of the phosphoenolpyruvate-dependent phosphotransferase system from Escherichia coli. Assignment of backbone resonances.

We have performed three-dimensional NMR studies on a central component of the phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli, denoted as HPr. The protein was uniformly enriched with 15N and 13C to overcome spectral overlap. Complete assignments were obtained for the backbone 1H, 15N and 13C resonances, using three-dimensional heteronuclear 1H NOE 1H-15N multiple-quantum coherence spectroscopy (3D-NOESY-HMQC) and three-dimensional heteronuclear total correlation 1H-15N multiple-quantum coherence spectroscopy (3D-TOCSY-HMQC) experiments on 15N-enriched HPr and an additional three-dimensional triple-resonance 1HN-15N-13C alpha correlation spectroscopy (HNCA) experiment on 13C, 15N-enriched HPr. Many of the sequential backbone 1H assignments, as derived from two-dimensional NMR studies [Klevit, R.E., Drobny, G.P. & Waygood, E.B. (1986) Biochemistry 25, 7760-7769], were corrected. Almost all discrepancies are in the helical regions, leaving the published antiparallel beta-sheet topology almost completely intact.

Bacterial Proteins↗
PubMed1992

Fetal Doppler velocimetry in the internal carotid and umbilical artery during Braxton Hicks' contractions.

Using Doppler ultrasound, previous studies revealed a considerable increase in vascular resistance in the uteroplacental circulation during Braxton Hicks' contractions. Consequently, uteroplacental blood flow is reduced and this affects placental oxygen transfer to the fetus, causing a fall in fetal arterial PO2. In view of the important role of arterial PO2 in the regulation of cerebral blood flow in the fetus, we hypothesised that Braxton Hicks' contractions cause a decrease in cerebral vascular resistance. A study was undertaken in 16 healthy near term pregnancies, using pulsed-wave Doppler ultrasound to evaluate the influence of Braxton Hicks' contractions on cerebral vascular resistance of the fetus. Flow velocity waveforms (FVWs) were recorded of the fetal internal carotid and umbilical artery and the Pulsatility Index (PI) was calculated. During Braxton Hicks' contractions the PI in the recorded vessels did not change. Fetal heart rate showed also no changes during Braxton Hicks' contractions. These findings indicate that resistance to blood flow downstream of these arteries, is not significantly altered, suggesting that Braxton Hicks' contractions have little or no effect on fetal haemodynamics and on fetal oxygenation in the healthy near term fetus.

Carotid Artery, Internal↗
PubMed1992

Uteroplacental Doppler velocimetry during Braxton Hicks' contractions.

Pulsed-wave Doppler ultrasound was used to evaluate the influence of Braxton Hicks' contractions on flow velocity waveforms in the uterine arteries. Flow velocity waveforms were obtained from a standardized site, at the crossing of the uterine artery with the external iliac artery near the uterine wall. Doppler signals were recorded in 16 healthy near-term nulliparous pregnant women. During Braxton Hicks' contractions, a considerable increase in pulsatility index (PI) was found in the uterine arteries increasing from 0.71 +/- 0.21 (mean +/- SD) to 1.14 +/- 0.67 (p < 0.005). Maternal heart rate decreased slightly but significantly during contractions. Despite the high PI values that were found during Braxton Hicks' contractions, a diastolic notch in the flow velocity waveform was never noticed. The findings indicate that during Braxton Hicks' contractions, resistance to blood flow in the uteroplacental circulation is considerably increased.

Adult↗
PubMed1990

Hairy cell leukemia preferentially expresses the IgG3-subclass.

Surface IgG expression of 29 cases of hairy cell leukemia (HCL) was assessed using IgG-subclass-specific monoclonal and F(ab)'2 polyclonal antibodies. A marked preference for the IgG3 subclass was found, as 16 of 19 IgG-positive HCL's expressed IgG3. In 10 cases, IgG3 was concurrently expressed with other heavy chains. No preferential IgG3 expression was observed in 11 IgG-positive non-Hodgkin's lymphomas. The marked predominance of IgG3 in HCL suggests a deviation in heavy chain class switching that may be related to the characteristically very low expression of LFA-1 and ICAM-1 molecules on hairy cells, and hence a defect in T-cell hairy cell interaction.

Antigens, Differentiation↗
PubMed1980

1H-NMR and photochemically-induced dynamic nuclear polarization studies on bovine pancreatic phospholipase A2.

Proton-NMR resonances of trytophan 3 and tyrosine 69 in bovine pancreatic phospholipase A2, its pro-enzyme and in Ala1-transaminated protein were assigned using photochemically-induced dynamic nuclear polarization (photo-CIDNP) as such or in combination with spin-echo measurements. In addition assignments were made by suppression of cross-relaxation effects using short (0.1 s) high-power laser pulses.

Animals↗
PubMedDate not supplied

Captopril improves recovery of adenosine triphosphate during reperfusion of the ischemic isolated rat heart; a 31-phosphorus-nuclear magnetic resonance study.

The effect of captopril on energy-rich phosphates and pH during normothermic ischemic arrest, hypothermic cardioplegic arrest and subsequent reperfusion was investigated in the isolated rat heart using 31P-nuclear magnetic resonance. The hearts remained in the probe during all perfusion procedures and captopril (80 ml.l-1) treatment was started directly after cannulation. After normothermic ischemic arrest (15 min), the ATP content of captopril-treated hearts was not significantly different from that of untreated hearts (53 +/- 9% and 52 +/- 8%, respectively). Accumulation of inorganic phosphate at the end of ischemia was significantly less in treated hearts, suggesting a higher end-ischemic nucleotide content in treated hearts. Hypothermic cardioplegic arrest (St. Thomas' Hospital solution, 4 degrees C) lasted for 3 h at 10 degrees C. Adenosine triphosphate in untreated hearts was significantly lower at the end of ischemia; 36 +/- 6% compared to 53 +/- 9% for untreated hearts. Adenosine triphosphate in untreated hearts recovered to 76 +/- 9% after normothermic ischemia and to 72 +/- 7% after hypothermic ischemia at the end of 30 min reperfusion. Captopril significantly improved adenosine triphosphate recovery in both treated groups; 89 +/- 4% after normothermic and 83 +/- 4% hypothermic ischemia. We conclude that captopril has a beneficial effect on recovery of adenosine triphosphate both after normothermic and after hypothermic ischemia.

Adenosine Triphosphate↗