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Reversible phosphorylation of proteins in proliferating and differentiating cells : cyclic variations and the effect of growth regulatorsFerreira, Gracinda Maria Nunes January 1994 (has links)
A Dissertation Submitted to the Faculty of Science
University of the Witwatersrand, Johannesburg
In fulfilment of the requirements
for the Degree of Doctor of Philosophy / Living cells are highly auto-dynamic entities which
means that the underlying biochemistry is equally
dynamic, a reality which is ignored by most researchers.
Theoretical studies indicate that such a state must be
due to the existence of oscillatory variations in the
levels and activities of key components in the cell. In
this study, the dynamic behaviour of four major,
interrelated areas of cell biochemistry
(phosphorylation, dephosphorylation, the terminal
reaction of glycolysis and the amount of soluble
protein) were examined and all systems found to
oscillate in murine erythroleukaemic cells (MEL) and,
where examined, also in the human HL-6Q leukaemic cell
line.
certain processes have been shown to be oscillatory for the first time ( phosphorylation
potential, the lactate dehydrogenase active isozyme level and aspects of the regulation thereof). While others have been shown to occur at a higher frequency
than previously reported (phosphotyrosine phosphatase
activity, the activity and apparent isozyme pattern of
lactate dehydrogenase, the amount of extractable
protein). All rhythms are shown (for the first time) to
be complex and to involve several contributing
periodicities, some modulating the period and amplitude
of the observed oscillation. The frequencies are very
high (periods of 1-20 minutes and probably Less) and the
amplitudes are equally high (variations in magnitude of
as much as a hundred fold).
Phosphorylation processes, currently of particular
interest with regard to the nature and control of cell
proliferation are thus found to be more highly dynamic
than previously believed, a fact which throws some doubt
on the current ideas on cell proliferation. The actual
lactate dehydrogenase (LDH) active isozyme pattern is
shown not to be constant (as generally believed) but to
vary at high frequency (possibly due to
phosphorylation of the the enzyme) while the kinetics
and specificity of the lone isozyme in murine
erythroleukaemic cells appear to be varying at
equally high frequency due to the action of
regulators (perhaps arising elsewhere within the
glycolytic pathway). Similar results were obtained with
HL-60 leukaemic cells with at least two of the
isozymes varying in level, to some extent independently.
The hormone, insulin, and the inducer of cell
differentiation, HMBA (hexamethylenebisacetamide), have
been found to affect the dynamics of the four systems
although, because of the complexity of the rhythms the
actual effects on the dynamics are not easily defined.
Insulin has a marked effect on the mean level of
the activity of the LDH isozyme.
The fact that all oscillations are seen despite no
attempt being made to synchronise the cell population
suggests the existence of communication between cells
but how this can occur when the rhythms are of such high
frequency is intriguing.
All the results add further support for the long
standing view of my supervisor, that the properties and
behaviour of cells reflect the internal dynamics and
that differentiation, cancer and intracellular
signalling occur through changes in the pattern of
temporal organisation of cellular oscillations. / AC2018
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Reversible phosphorylation of proteins in proliferating and differentiating cells: cyclic variations and the effect of growth regulatorsFerreira, Gracinda Maria Nunes January 1994 (has links)
A Dissertation Submitted to the Faculty of Science
University of the Witwatersrand, Johannesburg
In fulfilment of the requirements
for the Degree of Doctor of Philosophy
Johannesburg 1994 / Living cells are highly auto-dynamic entities which means that the
underlying biochemistry is equally dynamic, a reality which is ignored
by most researchers.
Theoretical studies indicate that such a state must be due to the
existence of oscillatory variations in the levels and activities of key components in the cell. In this study, the dynamic behaviour of four
major, interrelated areas of cell biochemistry (phosphorylation,
dephosphorylation, the terminal reaction of glycolysis and the amount
of soluble protein) were examined and all systems found to oscillate
in murine erythroleukaemic cells (MEL) and, where examined, also
in the human HL-6Q leukaemic cell line. [Abbreviated Abstract. Open document to view full version] / MT2017
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Turf retardation and weed control in common Kentucky bluegrass by CGA-17020 and CGA-24705Howell, Sandra L. January 2011 (has links)
Digitized by Kansas Correctional Industries
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An efficient switched capacitor buck-boost voltage regulator using delta-sigma control loopRao, Arun 29 April 2002 (has links)
Voltage converters or charge pumps find their use in many circuits. They are
extensively used in hand held devices as cell phones, pagers, PDA's and laptops.
Some of the important issues relating to design of voltage regulators for handheld
devices are size, efficiency and noise. Another important factor to be considered is
the discharge characteristic of the various batteries used by the handheld devices.
This thesis addresses the issues of tones present in the conventional switched
capacitor voltage regulator. An alternate architecture with a delta-sigma control
loop to eliminate this problem is proposed. Also discussed is a method to compute
the efficiency of switched capacitor charge pumps. A test chip implementing the new
architecture was fabricated in a 0.72-micron CMOS process. The results of the test
chip verify the improved architecture. / Graduation date: 2002
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Structural studies of the Ro ribonucleoprotein and the metalloregulator CsoRRamesh, Arati 15 May 2009 (has links)
Ro ribonucleoproteins are antigenic protein-RNA particles that are the major targets of the immune reaction in autoimmune disorders like systemic lupus erythematosus. The Ro protein has been implicated in cellular RNA quality control, due to its preference for binding misfolded non-coding RNAs such as pre5S ribosomal RNAs and U2 small-nuclear RNAs besides binding cytoplasmic RNAs called Y RNAs. Although well characterized in eukaryotes, an understanding of Ro in prokaryotes is lacking. To gain structural insight into Ro-RNA interactions we have determined a high resolution crystal structure of Rsr, a Ro ortholog from the bacterium D. radiodurans. The structure of Rsr reveals two domains- a flexible, RNA binding HEAT repeat domain and a cation binding vonWillebrand factor A domain. Structural differences between Rsr and Xenopus laevis Ro at the misfolded non-coding RNA binding site suggest a possible conformational switch in Ro that might enable RNA binding. Structural and biochemical characterization reveals that Ro binds cytoplasmic small RNAs called Y RNAs with low nanomolar affinity, to form ~700kDa multimers. Formation of these multimers suggests one possible mode by which Ro RNAs may be targeted towards downstream processing events. Metal responsive transcriptional regulators sense specific metals in the cells and regulate the expression of specific operons involved in export, import or sequestration of the metal. CsoR is a copper(I) specific transcriptional regulator of the cso operon which consists of a putative copper export pump, CtpV. In copper limiting conditions, CsoR binds the operator/promoter region of the cso operon. In increased concentrations of copper (I), CsoR binds copper (I) with high affinity and is released from the operator/promoter site, causing derepression of the cso operon. To gain structural insight into CsoR function, we have solved the crystal structure of copper(I) bound CsoR. The structure reveals a homodimer with a subunit bridging copper site. The trigonal planar geometry and the presence of cysteine and histidine ligands at the metal site are favorable for copper(I) binding. The structure reveals a novel DNA binding fold in CsoR, making it the founding member of a new structural class of metalloregulators.
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Structural studies of the Ro ribonucleoprotein and the metalloregulator CsoRRamesh, Arati 15 May 2009 (has links)
Ro ribonucleoproteins are antigenic protein-RNA particles that are the major targets of the immune reaction in autoimmune disorders like systemic lupus erythematosus. The Ro protein has been implicated in cellular RNA quality control, due to its preference for binding misfolded non-coding RNAs such as pre5S ribosomal RNAs and U2 small-nuclear RNAs besides binding cytoplasmic RNAs called Y RNAs. Although well characterized in eukaryotes, an understanding of Ro in prokaryotes is lacking. To gain structural insight into Ro-RNA interactions we have determined a high resolution crystal structure of Rsr, a Ro ortholog from the bacterium D. radiodurans. The structure of Rsr reveals two domains- a flexible, RNA binding HEAT repeat domain and a cation binding vonWillebrand factor A domain. Structural differences between Rsr and Xenopus laevis Ro at the misfolded non-coding RNA binding site suggest a possible conformational switch in Ro that might enable RNA binding. Structural and biochemical characterization reveals that Ro binds cytoplasmic small RNAs called Y RNAs with low nanomolar affinity, to form ~700kDa multimers. Formation of these multimers suggests one possible mode by which Ro RNAs may be targeted towards downstream processing events. Metal responsive transcriptional regulators sense specific metals in the cells and regulate the expression of specific operons involved in export, import or sequestration of the metal. CsoR is a copper(I) specific transcriptional regulator of the cso operon which consists of a putative copper export pump, CtpV. In copper limiting conditions, CsoR binds the operator/promoter region of the cso operon. In increased concentrations of copper (I), CsoR binds copper (I) with high affinity and is released from the operator/promoter site, causing derepression of the cso operon. To gain structural insight into CsoR function, we have solved the crystal structure of copper(I) bound CsoR. The structure reveals a homodimer with a subunit bridging copper site. The trigonal planar geometry and the presence of cysteine and histidine ligands at the metal site are favorable for copper(I) binding. The structure reveals a novel DNA binding fold in CsoR, making it the founding member of a new structural class of metalloregulators.
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Contingency ranking for on-line voltage stability assessment /Jia, Zhihong, January 1999 (has links)
Thesis (M.Eng.), Memorial University of Newfoundland, 2000. / Bibliography: leaves 115-118.
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AC mains voltage regulation by solid-state power conversiontechniques侯經權, Hau, King-kuen. January 1990 (has links)
published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy
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Auxin relations in a dwarf nana₁?allele of Zea mays L.Salih, Abbas Ahmed, 1929- January 1958 (has links)
No description available.
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The effects of gibberellin on alfalfa seedlingsNelson, Roy A., 1930- January 1959 (has links)
No description available.
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