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Biomedical subjects

M Fennema

Publications and source records attributed to M Fennema.

At least 19 recordsLinked to original sources
PubMed1999

Design and synthesis of reagents for phage display screening of dehalogenases.

Bifunctional molecules containing both a biotin and a substrate unit have been designed and synthesized for phage display screening of mutant libraries of haloalkane dehalogenase enzymes. The molecules were assembled using a convergent modular synthetic strategy. One molecule was synthesized to evaluate the concept of covalent capture and a second for screening of phage libraries for enantioselectivity.

Alkyl and Aryl Transferases↗
PubMed1999

A bacterial haloalkane dehalogenase gene as a negative selectable marker in Arabidopsis.

The dhlA gene of Xanthobacter autotrophicus GJ10 encodes a dehalogenase which hydrolyzes dihalo- alkanes, such as 1, 2-dichloroethane (DCE), to a halogenated alcohol and an inorganic halide (Janssen et al. 1994, Annu. Rev. Microbiol. 48, 163-191). In Xanthobacter, these alcohols are further catabolized by alcohol and aldehyde dehydrogenase activities, and by the product of the dhlB gene to a second halide and a hydroxyacid. The intermediate halogenated alcohols and, in particular, the aldehydes are more toxic than the haloalkane substrates or the pathway products. We show here that plants, including Arabidopsis, tobacco, oil seed rape and rice, do not express detectable haloalkane dehalogenase activities, and that wild-type Arabidopsis grows in the presence of DCE. In contrast, DCE applied as a volatile can be used to select on plates or in soil transgenic Arabidopsis which express dhlA. The dhlA marker therefore provides haloalkane dehalogenase reporter activity and substrate dependent negative selection in transgenic plants.

Arabidopsis↗
PubMed1997

Primary structure and catalytic mechanism of the epoxide hydrolase from Agrobacterium radiobacter AD1.

The epoxide hydrolase gene from Agrobacterium radiobacter AD1, a bacterium that is able to grow on epichlorohydrin as the sole carbon source, was cloned by means of the polymerase chain reaction with two degenerate primers based on the N-terminal and C-terminal sequences of the enzyme. The epoxide hydrolase gene coded for a protein of 294 amino acids with a molecular mass of 34 kDa. An identical epoxide hydrolase gene was cloned from chromosomal DNA of the closely related strain A. radiobacter CFZ11. The recombinant epoxide hydrolase was expressed up to 40% of the total cellular protein content in Escherichia coli BL21(DE3) and the purified enzyme had a kcat of 21 s-1 with epichlorohydrin. Amino acid sequence similarity of the epoxide hydrolase with eukaryotic epoxide hydrolases, haloalkane dehalogenase from Xanthobacter autotrophicus GJ10, and bromoperoxidase A2 from Streptomyces aureofaciens indicated that it belonged to the alpha/beta-hydrolase fold family. This conclusion was supported by secondary structure predictions and analysis of the secondary structure with circular dichroism spectroscopy. The catalytic triad residues of epoxide hydrolase are proposed to be Asp107, His275, and Asp246. Replacement of these residues to Ala/Glu, Arg/Gln, and Ala, respectively, resulted in a dramatic loss of activity for epichlorohydrin. The reaction mechanism of epoxide hydrolase proceeds via a covalently bound ester intermediate, as was shown by single turnover experiments with the His275 --> Arg mutant of epoxide hydrolase in which the ester intermediate could be trapped.

Amino Acid Sequence↗
PubMed1992

Continuous intra-arterial PO2 monitoring during thoracic surgery.

Intermittent blood gas sampling has several disadvantages, the most important being that samples are usually taken at set intervals, or when changes in oxygenation are suspected--when it is too late. Another problem is inaccuracy caused by careless blood sample handling. Continuous intravascular PaO2 monitoring eliminates these problems. This study shows that the Continucath sensor is an easy-to-use and reliable monitor, with specific early warning capabilities for hypoxia, thereby improving anesthetic and intensive care management. Its characteristics are: a stabilization period of 10 minutes, a 90% response time of 90 seconds, temperature dependence of 4% per degree celsius, a flow dependence of less than 1% if the flow is more than 5 cm/sec, a drift of less than 0.7% per hour, a correlation coefficient of 0.92 when compared to blood gas analysis during surgery.

Adult↗
PubMed1992

pO2-profiles in human muscle tissue as indicator of therapeutical effect in septic shock patients.

Automatically stepwise driven pO2 electrodes were transcutaneously inserted into muscle tissue of severely ill septic shock patients. The pO2 profile was plotted from 200 individual measurements registered during 5 minutes and a histogram plotted for documentation. Arterial and venous blood gases, cardiac output, systemic and pulmonary vascular resistance were measured continuously on-line. In septicemia multiple drug schemes are suggested all intending to increase oxygen supply to the tissue and to improve oxygen demand/supply mismatch. So far the attending physician is bound to conclude and continue respectively change the treatment scheme according to the above described macrophysiological parameters. Perfusion distribution and local inhomogenities of tissue oxygen supply remain undetected. In the described study pretreatment pO2 profiles in musculus quadriceps femoris were obtained and measurements repeated in intervals of 10 minutes after start of pharmacological treatment. The changes of pO2 profiles of 20 patients, monitored in such a way over days and weeks, were carefully correlated to the described cardiocirculatory parameters and blood gas analyses. Dopamine was used to improve cardiac function and tissue oxygen supply as well. The investigations show that resulting changes of cardiovascular and blood gas parameters do not always indicate that tissue oxygen supply has really improved. On the other hand there was never an improvement in tissue oxygen supply when no changes of the other parameters had occurred. It is advised to add as a further diagnostic parameter tissue pO2 measurements to get insight if improvement in cardiac and pulmonary function really has the intended effect of improvement of tissue oxygen supply.

Autoanalysis↗
PubMed1992

Myocardial oxygen supply under critical conditions, the effects of hemodilution and fluorocarbons.

This article reviews the factors influencing myocardial oxygen supply and demand. The regulative mechanisms in coronary blood flow, especially in critical conditions, are explained. Myocardial oxygenation in coronary artery disease is discussed with special reference to pharmacological intervention. An extensive evaluation of the effects of hemodilution on both the healthy and diseased heart is presented. Effects of hemodilution with fluorocarbons for the treatment or prevention of myocardial ischemia are shown with the aid of intramyocardial oxygen partial pressure measurements.

Animals↗
PubMed1990

Cardiovascular responses, hemodynamics and oxygen transport to tissue during moderate isovolemic hemodilution in pigs.

In conclusion, in contrast to many reports obtained from dogs, in pigs the rise in CO during moderate isovolemic hemodilution is, besides the increased venous return, more induced by increased work performance of the heart and less by a decreased SVR. The rise in CO did not compensate for the decrease in oxygen transport capacity. Our results confirm most of the reported findings in humans at the same stage of hemodilution. Besides changes in hemodynamics, in our study a gradual decreased oxygen affinity of hemoglobin could be observed. That the pig animal model for studying hemodilution and oxygen transport to the tissue is more appropriate than the dog model is open to discussion.

Animals↗
PubMed1989

Tissue oxygen tension in the cerebral cortex of the rabbit.

Polarographic techniques were employed to measure oxygen partial pressure using 10 micron glass-protected gold microelectrodes. When inserting the electrode into the cortex, a PO2-profile is produced. The average PO2 was about 9 mm Hg. Nearly all measurements were below 25 mm Hg and measurements above 50 mm Hg were rare. When the FiO2 was increased from 0.3 to 1.0, tissue PO2 increased, then gradually decreased. This is probably due to vasoconstriction of pre-capillary sphincters. Acute hypoxia showed the opposite effect, but the autoregulation does not seem to be so effective. When CO2 was added to the inspiratory gas mixture the PO2 increased and showed little tendency to return to normal values. This increase in PO2 is due to the direct effect of CO2 and H+ on the blood vessels, causing vasodilation, and therefore an increase in blood flow and tissue oxygenation.

Animals↗
PubMed1988

Myocardial oxygen tensions during ischaemia in fluorocarbon diluted pigs.

Previous work by the authors has shown that, following ligation of the left anterior descending coronary artery (LAD), myocardial oxygen tension (PmO2) in expected areas of maximal ischaemia is maintained at the expense of ischaemic border zones of the infarct area. Post-ischaemic haemodilution with the fluorocarbon containing plasma substitute Fluosol-DA 20% (FDA) could significantly improve PmO2 and pre-ischaemic haemodilution can delay myocardial ischaemia. We now present an analysis of the pattern of PmO2 changes to be seen when myocardial ischaemia is induced following prior haemodilution with FDA. Two groups of juvenile Yorkshire pigs were anaesthetised with intraperitoneal thiopentone, intubated and ventilated with halothane, nitrous oxide and oxygen. After placement of cardiovascular monitoring lines, a thoracotomy was performed. The pericardium was opened and 4 steel-protected gold microelectrodes were placed in the terminal supply area of the LAD in such a way that 2 electrodes were in the area of myocardial ischaema to be produced. One group of pigs were bled (20 ml/kg) and the loss was replaced with equal volumes of FDA. The animals were ventilated with halothane and oxygen and the terminal LAD was ligated. Electrode outputs were recorded on a flat bed recorder and analysed. LAD occlusion in the control animals resulted in similar changes in PmO2 to those described above.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Protection against myocardial ischaemia by prior haemodilution with fluorocarbon emulsions.

The possible prophylactic effects of Fluosol-DA 20% (FDA) haemodilution against myocardial hypoxia were studied in two groups of anaesthetized immature pigs. Precalibrated 200-micron diameter oxygen microelectrodes were inserted to the myocardium of the left ventricle. One group of animals was haemodiluted with FDA and both groups received 100% oxygen (plus halothane). The lower one-third of the left anterior descending coronary artery was occluded; this caused no significant cardiovascular changes. Analysis from the microelectrodes in the most hypoxic areas of the myocardium revealed significant decreases in myocardial oxygen tension (PmO2) in the control group 15 min after occlusion in the FDA-diluted group. Analysis of other electrodes suggested greater hyperaemic compensatory response in ischaemic border areas in the FDA-treated group.

Animals↗
PubMed1988

Aprotinin reduces hypothermic mortality--an experimental model.

In order to test the postulate that post-hypothermic damage may be caused by protease activation, the effect of the administration of aprotinin on hypothermic mortality was investigated in anaesthetized rabbits. A group of 6 animals received 40.000 KIU aprotinin intravenously prior to the induction of hypothermia by surface cooling and this was followed by a further 35.000 KIU each hour for 5 h. The animals were cooled to 29 degrees C and then rewarmed. A control group received equal volumes of physiological saline. The aprotinin treated animals survived, whereas all the control group died within 7 days, 5 of them within 24 h. The haemodynamic, biochemical and haematological changes in the two groups are reported.

Animals↗
PubMed1986

Effects of haemodilution with fluorocarbons or dextran on oxygen tensions in the acutely ischaemic myocardium.

The effect of haemodilution with dextran or with oxygen transporting fluorocarbons (Fluosol-DA 20%) on myocardial oxygen tension (PmO2) during experimental myocardial ischaemia was studied in pigs. Polarographic oxygen microelectrodes were introduced 3 mm to the left ventricle wall and the distal one-third of the left anterior descending coronary artery (LAD) was occluded. Anaesthesia was maintained with 0.5% halothane in oxygen to ensure maximal oxygen content of the fluorocarbons. The animals were divided into three groups of five animals each. In group I no treatment was given and in groups II and III, after bleeding 20 ml kg-1, haemodilution was performed with Fluosol-DA 20% or 5% dextran respectively. Occlusion of the LAD caused no significant changes in cardiovascular vascular variables and only in group III (dextran) were significant effects of haemodilution observed. LAD occlusion caused highly significant decreases in PmO2. After haemodilution, PmO2 in the Fluosol group II (in contrast to groups I and III) was no longer significantly different from pre-occlusion values. After 5 h of occlusion, mean PmO2 in this group had returned to 92.2% of the pre-occlusion values, whereas in groups I and III it was 27.8% and 33.7%, respectively.

Animals↗