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Regulation of ribonucleotide reductase analyzed by simultaneous measurement of the four enzyme activitiesHendricks, Stephen P. 12 March 1998 (has links)
The first committed step in DNA biosynthesis occurs by direct reduction of
ribonucleotides. This reduction is catalyzed by ribonucleotide reductase (RNR), an
enzyme which uses a unique radical mechanism to facilitate the transformation. All four
DNA precursors are synthesized by a single enzyme. Therefore, an intricate pattern of
regulation has evolved to insure that RNR generates the proper quantity of each
deoxyribonucleotide. It is this regulation, and conditions that influence this regulation,
that are the central focal points of this dissertation.
The studies described in this thesis have been aided by the development of a novel
RNR assay. Unlike the traditional assay, this new procedure permits the simultaneous
monitoring of all four RNR activities. This four-substrate assay was used to investigate
whether the four enzyme activities of RNR were differentially sensitive to inhibition by the
radical scavenger, hydroxyurea. The assay results, along with the results of a technique
that measured enzyme inhibition as a function of radical decay, suggest that all activities of
RNR are equally inhibited by hydroxyurea. Instead of differential inhibition, it appears
that the activity level of RNR determines the relative sensitivity to hydroxyurea.
The effects of nucleotide effectors and substrates on the relative turnover rates of the
vaccinia virus and T4 phage RNR were also investigated by use of the four-substrate
assay. When physiological concentrations of the allosteric effectors and substrates were
added to the reaction mixtures, both enzyme forms produced dNDPs in ratios that
approximate the nucleotide composition of their respective genomes. Non-physiological
nucleotide concentrations generated significantly different product profiles, indicating that
RNR has evolved to function within a defined nucleotide environment. Interestingly, the
substrate component of the nucleotide environment proved to be as important as the
allosteric effectors in modulating the reaction rates. Although the allosteric effects of
nucleoside triphosphates have been known for some time, little attention has been given to
the potential role that substrates play in the regulation of RNR. The results from my
research suggest that the regulation of RNR in vivo results from a complex interplay
between the enzyme and its substrates, products, and allosteric effectors. / Graduation date: 1998
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Regulation of sorbitol metabolism by glucose in Clostridium pasteurianumRoohi, Mohammad Sadegh January 1987 (has links)
No description available.
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Regulation of inositol phospholipid hydrolysis by extended treatment with angiotensin II in human aortic smooth muscle cellsNiibori, Yoshiko 06 March 2003 (has links)
Long-term stimuli of many systems leads to decreased cellular
responsiveness, or desensitization. We characterized the desensitization of
angiotensin II (Ang 11)-mediated inositol phospholipid (IP) hydrolysis in cultured
human aortic smooth muscle cells (HASMC). Although it has been suggested that
the desensitization induced by long-term Mg II exposure may result partially from
down-regulation of Ang II receptor, this is not sufficient to explain fully
desensitization in many systems. Post-receptor desensitization of IP hydrolysis
may also result from phosphorylation or changes in protein levels of the effector
enzyme, PLC-β. We identified the major PLC-β isoenzymes expressed by
HASMC as PLC-β1 and PLC-β3. Ang II pretreatment reduced IP accumulation
induced by Ang II (1μM) in a time-dependent manner. Phorbol ester-12-myristrate-13-acetate (PMA), a protein kinase C (PKC) activator, also reduced
Ang II-stimulated IP accumulation. These results suggest that PKC activation may
negatively regulate Ang II-stimulated IP signaling in HASMC, similar to rat cells.
In addition, PKC also reduced IP accumulation stimulated by A1F₄⁻, directly
activating the G protein. It suggests that the majority of PKC-induced
desensitization of Ang II-stimulated IP signaling occurs downstream of the Ang II
receptor in HASMC. However, both PLC-β1 and PLC-β3, expected candidates for
PKC phosphorylation, were phosphorylated independently of PKC activation or
inhibition, indicating that PKC might not be involved in direct phosphorylation of
PLC-β1 and PLC-β3. Furthermore, PLC-β1, but not PLC-β3, was highly
phosphorylated under basal conditions, suggesting that PLC-β1 and PLC-β3 may
play different roles in IP signaling in HASMC. / Graduation date: 2003
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An electrophoretic investigation of some metabolic enzymes in the Japanese eel, Anguilla japonica蔡昌明, Tsoi, Chang-ming, Stephen. January 1984 (has links)
published_or_final_version / Zoology / Master / Master of Philosophy
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Evaluation of Immobilized Boronates for Studies of Adenine Nucleotide MetabolismAlvarez-Gonzalez, Rafael 08 1900 (has links)
Immobilized boronates were evaluated for studies of adenine nucleotide metabolism. These studies were performed using Affi-gel 601, a commercial boronate gel, and dihydroxyboryl Sepharose and dihydroxyboryl-Bio Rex which were synthesized in the laboratory. The studies performed included the determination of the relative binding affinity of a variety of adenine containing compounds for the three immobilized boronates under differing chromatographic conditions.
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Insect carbohydrate metabolism: partial purification of insulin-like peptides and some effects of vertebrate hypoglycemic agents in insectsJacobs, Ruth. January 1979 (has links)
Call number: LD2668 .T4 1979 J32 / Master of Science
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Regulation of cellulose metabolism during growth of Pisum sativumSpencer, Frederick Sherman. January 1975 (has links)
No description available.
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Biochemical and genetic approach to the characterisation of Tec function in the mouseAtmosukarto, Ines Irene Caterina. January 2001 (has links) (PDF)
Copy of author's previously published work inserted. Includes bibliographical references (leaves 160-182). Concentrates mainly on the characterisation of the molecular mechanism of action of the tec protein tyrosine kinase using biochemical and genetic approaches.
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Biophysical analysis of Tec Kinase regulatory regions : implications for the control of Kinase activityPursglove, Sharon Elizabeth. January 2001 (has links) (PDF)
Bibliography: leaves 139-165.
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Biophysical analysis of Tec Kinase regulatory regions : implications for the control of Kinase activity / by Sharon Elizabeth Pursglove.Pursglove, Sharon Elizabeth January 2001 (has links)
Bibliography: leaves 139-165. / ix, 183 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Biochemistry, 2001
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