Biomedical subjects

M K Olsen

Publications and source records attributed to M K Olsen.

12 recordsLinked to original sources

PubMed2006

Generating controllable atom-light entanglement with a Raman atom laser system.

We introduce a scheme for creating continuous variable entanglement between an atomic beam and an optical field, by using squeezed light to outcouple atoms from a Bose-Einstein condensate via a Raman transition. We model the full multimode dynamics of the atom laser beam and the squeezed optical field and show that, with appropriate two-photon detuning and two-photon Rabi frequency, the transmitted light is entangled in amplitude and phase with the outcoupled atom laser beam. The degree of entanglement is controllable via changes in the two-photon Rabi frequency of the outcoupling process.

Journal Article↗

PubMed2005

Einstein-Podolsky-Rosen correlations via dissociation of a molecular Bose-Einstein condensate.

Recent experimental measurements of atomic intensity correlations through atom shot noise suggest that atomic quadrature phase correlations may soon be measured with a similar precision. We propose a test of local realism with mesoscopic numbers of massive particles based on such measurements. Using dissociation of a Bose-Einstein condensate of diatomic molecules into bosonic atoms, we demonstrate that strongly entangled atomic beams may be produced which possess Einstein-Podolsky-Rosen (EPR) correlations in field quadratures in direct analogy to the position and momentum correlations originally considered by EPR.

Journal Article↗

PubMed2001

Quantum superchemistry: dynamical quantum effects in coupled atomic and molecular Bose-Einstein condensates.

We show that in certain parameter regimes there is a macroscopic dynamical breakdown of the Gross-Pitaevskii equation. Stochastic field equations for coupled atomic and molecular condensates are derived using the functional positive- P representation. These equations describe the full quantum state of the coupled condensates and include the commonly used Gross-Pitaevskii equation as the noiseless limit. The full quantum theory includes the spontaneous processes which will become significant when the atomic population is low. The experimental signature of the quantum effects will be the time scale of the revival of the atomic population after a near total conversion to the molecular condensate.

Journal Article↗

PubMed2001

Disease mechanisms revealed by transcription profiling in SOD1-G93A transgenic mouse spinal cord.

Mutations of copper,zinc-superoxide dismutase (cu,zn SOD) are found in patients with a familial form of amyotrophic lateral sclerosis. When expressed in transgenic mice, mutant human cu,zn SOD causes progressive loss of motor neurons with consequent paralysis and death. Expression profiling of gene expression in SOD1-G93A transgenic mouse spinal cords indicates extensive glial activation coincident with the onset of paralysis at 3 months of age. This is followed by activation of genes involved in metal ion regulation (metallothionein-I, metallothionein-III, ferritin-H, and ferritin-L) at 4 months of age just prior to end-stage disease, perhaps as an adaptive response to the mitochondrial destruction caused by the mutant protein. Induction of ferritin-H and -L gene expression may also limit iron catalyzed hydroxyl radical formation and consequent oxidative damage to lipids, proteins, and nucleic acids. Thus, glial activation and adaptive responses to metal ion dysregulation are features of disease in this transgenic model of familial amyotrophic lateral sclerosis.

Age of Onset↗

PubMed2000

Social support and quality of life in patients with coronary artery disease.

The relationship between perceived social support and domain-specific health-related quality of life (HRQOL) was examined in a sample of cardiac catheterization patients after considering age, gender, race, education, and coronary artery disease (CAD) severity. Data was collected on 4,278 cardiac catheterization patients (63% males) and included 1,215 patients with non-significant CAD and 3,063 patients who had significant CAD ( > or = 75% stenosis of at least one major coronary artery). Among the patients with significant CAD, 2,721 were classified as low disease severity and 342 were considered high disease severity. Regression models indicated that a lack of social support was associated with significantly lower levels of HRQOL across all eight SF-36 HRQOL domains after considering disease severity and other demographic factors. The models also indicated that social support and other relevant variables interacted across various HRQOL domains. Physical function and physical role function were lower with age, whereas mental health, emotional role function, and vitality were higher with age. Females reported lower HRQOL than males across all domains. Minority patients reported lower levels of HRQOL than white patients across four domains. Increased disease severity was related to lower levels among four of the eight HRQOL domains. The observed interactions of social support with minority status, disease severity, and education suggest that a subset of individuals may suffer lower levels of HRQOL. These individuals may subsequently require the greatest degree of care and potentially benefit most from intervention.

Adult↗

PubMed1998

KT5720 and U-98017 inhibit MAPK and alter the cytoskeleton and cell morphology.

We previously identified KT5720 and U-98017 as agents that had paclitaxel (taxol)-like activity in a Chinese hamster ovary (CHO) paclitaxel-dependent cell screen for paclitaxel mimetics. In vitro polymerization of purified brain tubulin is not affected substantially by these compounds, suggesting that, unlike paclitaxel, these agents do not directly affect tubulin. However, these compounds cause profound rearrangements of the cytoskeleton in intact cells, including an apparent alteration of microtubule length, overlapping of cells, and an increase in cell size. We show that KT5720 and U-98017 effectively inhibit mitogen-activated protein kinase (MAPK) activity in vitro. Staurosporine, a poor inhibitor of MAPK but a potent inhibitor of cAMP-dependent protein kinase A (PKA) activity, phospholipid/Ca++-dependent kinase (PKC), and cdc2, does not cause similar changes. In addition, paclitaxel-dependent cells grown in U-98017 have substantially decreased levels of stimulated MAPK. In correlation with these results, we have confirmed the presence of MAPK in isolated tubulin and microtubules in cells. We have examined the hypothesis that these compounds are working through inhibition of MAPK to alter microtubules by inhibiting the phosphorylation of microtubule-associated proteins. A MAPKK dominant negative mutation transfected in CHO cells inhibits activation of MAPK. Transfectants carrying this dominant mutant have impaired activation of MAPK and an altered cell morphology, similar in some respects to that seen with KT5720 and U-98017. These results support a role for MAPK family members in the control of microtubule dynamics and suggest that in intact cells U-98017 and KT5720 achieve their effects of altering cytoskeleton and supporting partial growth of paclitaxel-dependent cells through inhibition of kinases such as MAPK.

Animals↗

PubMed1993

Isolation and analysis of novel mutants of Escherichia coli prlA (secY).

Plasmid libraries of prlA mutants containing single-base-pair changes throughout the gene were generated by in vitro random mutagenesis. The prlA mutations capable of suppressing the secretion defect of LamB caused by mutations in the LamB signal peptide were selected and analyzed. Together with additional mutations generated by site-directed mutagenesis, a number of novel prlA mutations and/or suppressors were identified. These mutations provide the starting points for studying the relationship of structure and function of PrlA in its interaction with LamB and/or other component(s) in the Escherichia coli protein secretion-translocation complex.

Amino Acid Sequence↗

PubMed1992

Stable production of an analog of human tissue plasminogen activator from cultured Drosophila cells.

We have studied the expression of an analog of human tissue plasminogen activator, FK2P, in Drosophila Schneider 2 cells. A number of promoters were tested, including the Drosophila metallothionein promoter (MTd), baculovirus immediate early promoter (IE), Drosophila copia promoter, mouse metallothionein promoter, cytomegalovirus immediate early promoter with or without intron, SV40 immediate early promoter, and human elongation factor 1 alpha promoter. Two of these promoters drove significant expression of FK2P. The MTd promoter is tightly regulated and upon induction with copper or cadmium expression of FK2P increases as much as 180-fold, accumulating in the culture medium to about 7 micrograms FK2P/10(6) cells/day as determined by ELISA. The IE promoter can direct the constitutive expression to yield about 0.4 microgram FK2P/10(6) cells/day. The production of FK2P in these cell lines remains at about the same level after repeated passages, even in the absence of selective pressure. The FK2P accumulated in the culture medium is fully active in an assay using a chromogenic substrate for serine proteases. Western immunoblot analysis shows that the product remains predominantly as single-chain molecules in serum-free medium, while in serum-containing medium two-chain material occurs as expected due to the presence of plasmin in serum. Judged from the size in Western immunoblots, the FK2P produced is glycosylated.

Amino Acid Sequence↗

PubMed1990

Substrate analogue inhibition and active site titration of purified recombinant HIV-1 protease.

The aspartyl protease of human immunodeficiency virus 1 (HIV-1) has been expressed in Escherichia coli at high levels, resulting in the formation of inclusion bodies which contain denatured insoluble aggregates of the protease. After solubilization of these inclusion bodies in guanidinium chloride, the protease was purified to apparent homogeneity by a single-step reverse-phase HPLC procedure. The purified, but inactive, protein was denatured in 8 M urea and refolded to produce the active protease. Enzyme activity was demonstrated against the substrate H-Val-Ser-Gln-Asn-Tyr-Pro-Ile-Val-OH, modeled after the cleavage region between residues 128 and 135 in the HIV gag polyprotein. With this substrate, a Vmax of 1.3 +/- 0.2 mumol/(min.mg) and KM of 2.0 +/- 0.3 mM were determined at pH 5.5. Pepstatin (Iva-Val-Val-Sta-Ala-Sta-OH) and substrate analogues with the Tyr-Pro residues substituted by Sta, by Phe psi [CH2N]Pro, and by Leu psi [CH(OH)CH2]Val inhibited the protease with KI values of 360 nM, 3690 nM, 3520 nM, and less than 10 nM, respectively. All were competitive inhibitors, and the tightest binding compound provided an active site titrant for the quantitative determination of enzymatically active HIV-1 protease.

Amino Acid Sequence↗

PubMed1990

A simple Escherichia coli system for monitoring HIV protease activity: analysis of two temperature-sensitive protease mutants.

A simple Escherichia coli system has been developed for the detection of human immunodeficiency virus (HIV) protease activity. In this system, the protease sequence is placed downstream of the HIV gag polypeptide in an operon arrangement. Upon expression of the operon, gag serves as the substrate for the protease; the level of protease activity can be determined by measurement of the cleavage product of gag in cell extracts by Western immunoblotting. This system is useful in both detection of protease mutations generated by mutagenesis and in testing substrate specificity of the protease by mutagenesis of the gag sequence. Using this system, we have observed that modification of the N-terminus of HIV protease renders the enzyme temperature sensitive; the temperature sensitivity is made more pronounced by the conserved change of valine to isoleucine at residue eleven.

Endopeptidases↗

PubMed1989

Effect of nucleotide sequences directly downstream from the AUG on the expression of bovine somatotropin in E. coli.

We have studied the expression of bovine somatotropin (BSt) to gain more understanding of various factors affecting translation in E. coli. The unmodified cDNA coding for mature bovine somatotropin does not produce significant amounts of BSt in E. coli using a pBR322-derived vector. However, a translation fusion with 16 codons from trpLE in front of BSt cDNA results in greater than 20% of total cell protein as the fusion product. Analysis of transcription by measuring the rate and integrity of the mRNA confirms that a post-transcriptional event is responsible for the poor expression of the BSt cDNA. There are two potential stem-loop structures in the 5' region of the mRNA which may interfere with translation. To study their effect on translation, lacZ fusions and oligonucleotide mutagenesis were carried out. The results demonstrate that the secondary structure involving the initiation codon blocks translation initiation. Removal of this stem-loop results in a 100-fold increase in BSt expression. However, the expression level is still low, amounting to only 0.5-1% of total cell protein. High level expression can be obtained by replacement of the beginning sequence of BSt cDNA with trpLE codons. These results suggest that in addition to the secondary structure, the nucleotide sequence or amino acid context within the beginning of BSt is incompatible with one of the steps in translation initiation.

Cloning, Molecular↗

PubMed1988

Use of lacZ expression to monitor transcription.

For use in monitoring transcription in operon fusion, we have constructed a lacZ sequence with the initiation codon ATG and the Escherichia coli consensus Shine-Dalgarno site. There are unique restriction endonuclease sites flanking the sequence to allow easy isolation of the lacZ sequence with or without the Shine-Dalgarno site. We have placed this lacZ sequence behind the bovine growth hormone (BGH) gene and found that the lacZ product beta-galactosidase synthesized reflects the level of BGH-specific mRNA.

Animals↗