21 Matching Results

Search Results

Advanced search parameters have been applied.

Chemical and physical characterization of the activation of ribulosebiphosphate carboxylase/oxygenase

Description: Molecular structure of ribulosebiphosphate carboxylase/oxygenase isolated from Rhodospirillium was compared with the enzyme isolated from Alcaligens eutrophus. Peptides derived from the active center of the bacterial enzyme were highly homologous with those isolated from spinach. Molecular shapes of the carboxylases were estimated using neutron scattering data. These studies suggested that the enzyme as isolated from R. rubrum is a solid prolate ellipsoid or cylinder, while the spinach enzyme resembles a hollow sphere. 1 drawing.
Date: January 1, 1983
Creator: Donnelly, M.I.; Ramakrishnan, V. & Hartman, F.C.
Partner: UNT Libraries Government Documents Department

Microbial Oxidation and Demethylation Processes in the Environmental Mercury Cycle

Description: This project demonstrated that bacterial catalase enzymes can convert unreactive Hg(0) to highly reactive Hg(II) ion. It also demonstrated the mechanism of the organomercural lyase, a bacterial enzyme which degrades methylmercury and other organomercurials. Lastly, it demonstrated the 3-dimensional structure of this enzyme by both solution NMR and by x-ray crystallography. These structures provide insights into the catalytic mechanism of the lyase that will allow engineering of variants with improved ability to degrade methylmercury.
Date: October 30, 2000
Creator: Summers, Anne O.
Partner: UNT Libraries Government Documents Department

The active site of ribulose-bisphosphate carboxylase/oxygenase

Description: The active site of ribulose-bisphosphate carboxylase/oxygenase requires interacting domains of adjacent, identical subunits. Most active-site residues are located within the loop regions of an eight-stranded {beta}/{alpha}-barrel which constitutes the larger C-terminal domain; additional key residues are located within a segment of the smaller N-terminal domain which partially covers the mouth of the barrel. Site-directed mutagenesis of the gene encoding the enzyme from Rhodospirillum rubrum has been used to delineate functions of active-site residues. 6 refs., 2 figs.
Date: January 1, 1991
Creator: Hartman, F.C.
Partner: UNT Libraries Government Documents Department

[Regulation of alternative CO[sub 2] fixation pathways in procaryotic and eucaryotic photosynthetic organisms]

Description: The major goal of this project is to determine how microorganisms regulate the assimilation of CO[sup 2] via pathways alternative to the usual Calvin reductive pentose phosphate scheme. In particular, we are interest in the molecular basis for switches in CO[sub 2] metabolic paths. Several earlier studies had indicated that purple nonsulfur photosynthetic bacteria assimilate significant amounts of CO[sub 2] via alternative non-Calvin routes. We have deleted the gene that encodes. RubisCo (ribulose bisphosphate carboxylase/oxygenase) in both the Rhodobacter sphaeroids and Rhodospirillum rubrum. The R. sphaeroides RubisCO deletion strain (strain 16) could not grow under photoheterotrophic conditions with malate as electron donor and CO[sub 2] as the electron acceptor; however the R. rub RubisCO deletion strain (strain I-19) could. Over the past year we have sought to physiologically characterize strain 16PHC. We found that, 16PHC exhibited rates of whole-cell CO[sub 2] fixation which were significantly higher than strain 16. Strain 16PHC could not grow photolithoautotrophically in a CO[sub 2] atmosphere; however, CO[sub 2] fixation catalyzed by photoheterotrophically grown 16PHC was repressed by the addition of DMSO. Likewise, we found that cells initially grown in the presence of DMSO could induce the CO[sub 2] fixation system when DMSO was removed. Thus, these results suggested that both PHC and I-19 could be used to study alternative CO[sub 2] fixation reactions and their significance in R. sphaexoides and R. rubrum.
Date: January 1, 1992
Partner: UNT Libraries Government Documents Department

Anaerobic bioprocessing of low-rank coals

Description: We are seeking to find biological methods to remove carboxylic functionalities from low-rank coals and to assess the properties of the modified coal towards coal liquefaction. The main objectives for this quarter were : continuation of microbial consortia development and maintenance, evaluation of commercial decarboxylase, decarboxylation of lignite, demineralized Wyodak coal and model polymer, and characterization of biotreated coals. Specifically we report that two batch fermentor systems were completed and three other fermentors under optimum conditions for coal decarboxylation are in progress; that inhibition of growth of methanogens in the batch fermentor system enhanced the carbon dioxide production; that adapted microbial consortium produced more gas from lignite than Wyodak subbituminous coal; that phenylalanine decarboxylase exhibited insignificant coal decarboxylation activity; that two different microbial consortia developed on coal seem to be effective in decarboxylation of a polymer containing free carboxylic groups; and that CHN analyses of additional biotreated coals reconfirm increase in H/C ratio by 3--6%.
Date: July 14, 1992
Creator: Jain, M.K.; Narayan, R. & Han, O.
Partner: UNT Libraries Government Documents Department

The potential effects of concurrent increases in temperature, CO sub 2 and O sub 3 on net photosynthesis, as mediated by rubisCO

Description: At the leaf level, under light saturating and light limiting conditions, it is shown that elevated atmospheric CO{sub 2} concentration not only alters the scale of the response of carbon gain to rising temperature, but can alter the direction of response. These points bring into serious question the value of any predictions of plant production which ignore not only the direct effect Of C0{sub 2} on carbon gain, but also the basic interactions of temperature, C0{sub 2} and 0{sub 3}. Whilst many factors may potentially diminish the enhancement of lightsaturated leaf photosynthetic rates with increase in atmospheric CO{sub 2} concentrations, no mechanism has so far been identified which could remove the parallel stimulation of light-limited photosynthesis.
Date: July 1, 1992
Creator: Long, S. (Brookhaven National Lab., Upton, NY (United States) Essex Univ., Colchester (United Kingdom). Dept. of Biology)
Partner: UNT Libraries Government Documents Department

Transposon-induced nuclear mutations that alter chloroplast gene expression

Description: The goal of this project is to use mutant phenotypes as a guide to nuclear genes that determine the timing and localization of chloroplast development The immediate goals are to identify nuclear mutants with defects in chloroplast gene expression from maize lines harboring active Mu transposons; characterize their phenotypes to determine the precise defect in gene expression; clone several of the most interesting mutations by exploiting the transposon tag; and use the clones to further define the roles of these genes in modulating chloroplast gene expression. Three mutants were described earlier that had global defects in chloroplast gene expression. We have found that two of these mutations are allelic. Both alleles have global defects in chloroplast translation initiation, as revealed by the failure to assemble chloroplast mRNAs into polysomes. We have isolated and characterized three new mutants from Mu lines that have novel defects in chloroplast RNA metabolism. We are now ready to begin the task of cloning several of these genes, by using the Mu transposon tag.
Date: January 1, 1992
Creator: Barkan, A.
Partner: UNT Libraries Government Documents Department

Role of pectolytic enzymes in the programmed separation of cells from the root cap of higher plants. Final report

Description: The objective of this research was to develop a model system to study border cell separation in transgenic pea roots. In addition, the hypothesis that genes encoding pectolytic enzymes in the root cap play a role in the programmed separation of root border cells from the root tip was tested. The following objectives have been accomplished: (1) the use of transgenic hairy roots to study border cell separation has been optimized for Pisum sativum; (2) a cDNA encoding a root cap pectinmethylesterase (PME) has been cloned; (3) PME and polygalacturonase activities in cell walls of the root cap have been characterized and shown to be correlated with border cell separation. A fusion gene encoding pectate lyase has also been transformed into pea hairy root cells.
Date: March 1, 1995
Creator: Hawes, M.C.
Partner: UNT Libraries Government Documents Department

Isocitrate lyase and the glyoxylate cycle. Progress report, February 16, 1992--February 15, 1993

Description: This progress report describes efforts directed at the active-site modification of isocitrate lyase (icl) of Escherichia coli. Studies are reported that describe the results of several amino acid substitutions gained by directed mutagenesis of the icl gene. Preliminary studies are also related in cloning, sequencing and expression of icl of watermelon.
Date: December 31, 1992
Creator: McFadden, B. A.
Partner: UNT Libraries Government Documents Department

6-Acetyldihydrohomopterin and sepiapterin affect some GTP cyclohydrolase I's and not others

Description: The first enzyme in pteridine biosynthesis, GTP cyclohydrolase I, is a likely site for regulation of pteridine biosynthesis to occur. GTP cyclohydrolase I responds to hormonal treatment and is found altered in a variety of mice with genetically based neurological and immunological disorders. Genetic loci can greatly modify the activity of GTP cyclohydrolase: Punch mutant in Drosophila hph-1 in mouse and atypical phenylketonuria in human. This report examines the ability of Ahp and sepiapterin to alter the activity of GTP cyclohydrolase I from mouse liver, rat liver and Drosophila head. 20 refs., 2 tabs.
Date: January 1, 1988
Creator: Jacobson, K.B. & Manos, R.E.
Partner: UNT Libraries Government Documents Department

Mechanism of activation of light-activated phosphodiesterase and evidence for homology with hormone-activated adenylate cyclase

Description: Light-activated cGMP phosphodiesterase (PDE) is one of the effector proteins in the rod outer segments in vertebrate retina. The hydrolysis of cGMP in rod occurs with a speed and light sensitivity which suggests a role for this hydrolysis in visual transduction. In fact, there is electrophysiological data which supports the possibility that cGMP could regulate rod membrane voltage. PDE shows very rapid activation in the presence of photons and GTP. We have called attention to the intriguing analogy between light activated rod phosphodiesterase and hormone activated adenylate cyclase. A number of studies have implicated the binding of GTP to a GTP binding protein as a factor in the hormone dependent activation of adenylate cyclase. Moreover, Cassel and Selinger have shown that hydrolysis of GTP is a component in the inactivation of the hormone dependent adenylate cyclase. We review here recent additional data which provide specific molecular details of the mechanism of light activation of rod PDE as well as demonstrate the exchange of components between light activated PDE and hormone activated cyclase.
Date: January 1, 1983
Creator: Bitensky, M.W.; Yamazaki, A.; Wheeler, M.A.; George, J.S. & Rasenick, M.M.
Partner: UNT Libraries Government Documents Department

Isocitrate lyase and the glyoxylate cycle. Progress report, July 1, 1988--February 15, 1989

Description: Studies on the structure, regulation and catalytic function of isocitrate lyase are reported. This catalyzes the first unique step i the glyoxylate cycle. In this cycle, lipids are converted to carbohydrates in a process which contributes to microbial growth on fatty aids and to the growth of oil-rich seedlings and animal embryos. These studies will provide basic information about isocitrate lyase. The function of this enzyme is vital to microbial growth (on fatty acids) and to the growth of varied plant seedlings and their subsequent utilization of solar energy.
Date: December 31, 1989
Creator: McFadden, B. A.
Partner: UNT Libraries Government Documents Department

/sup 35/Cl and /sup 81/Br nuclear magnetic resonance studies of carbonic anhydrase

Description: /sup 35/Cl NMR studies substantiated the binding of Cl/sup -/ to the Zn(II) of carbonic anhydrase. Zinc-free carbonic anhydrase was prepared and it exhibited essentially no effect on the Cl/sup -/ line width. The net Cl/sup -/ line width increased with temperature. /sup 81/Br NMR was quite similar to /sup 35/Cl in that its relaxation is dominated by quadrupolar interactions.
Date: February 1, 1979
Creator: Ward, R.L.
Partner: UNT Libraries Government Documents Department

[Regulation of terpene metabolism]

Description: During the last grant period, we have completed studies on the key pathways of monoterpene biosynthesis and catabolism in sage and peppermint, and have, by several lines of evidence, deciphered the rate-limiting step of each pathway. We have at least partially purified and characterized the relevant enzymes of each pathway. We have made a strong case, based on analytical, in vivo, and in vitro studies, that terpene accumulation depends upon the balance between biosynthesis and catabolism, and provided supporting evidence that these processes are developmentally-regulated and very closely associated with senescence of the oil glands. Oil gland ontogeny has been characterized at the ultrastructural level. We have exploited foliar-applied bioregulators to delay gland senescence, and have developed tissue explant and cell culture systems to study several elusive aspects of catabolism. We have isolated pure gland cell clusters and localized monoterpene biosynthesis and catabolism within these structures, and have used these preparations as starting materials for the purification to homogeneity of target regulatory'' enzymes. We have thus developed the necessary background knowledge, based on a firm understanding of enzymology, as well as the necessary experimental tools for studying the regulation of monoterpene metabolism at the molecular level. Furthermore, we are now in a position to extend our systematic approach to other terpenoid classes (C[sub 15]-C[sub 30]) produced by oil glands.
Date: January 1, 1991
Creator: Croteau, R.
Partner: UNT Libraries Government Documents Department

Attempts to apply affinity labeling techniques to ribulosebisphosphate carboxylase/oxygenase. [Comparison of spinach leaf and Rhodospirillum rubrum]

Description: Studies on carboxylases/oxygenases from different species may be necessary to confirm that a residue implicated as essential is indeed an active-site component. To provide an especially stringent test case for the identification of species invariant structural features the enzymes from two phylogenetically distant species, spinach and Rhodospirillum rubrum, were compared. To date, the reactions of Br-butanone-P/sub 2/ and BrAcNHEtOP with the spinach enayme have been rather thoroughly characterized; only preliminary experiments have been completed with the R. rubrum enzyme. Both enzymes were isolated and assayed for carboxylase activity (spectrophotometrically or /sup 14/CO/sub 2/-fixation) and for oxygenase activity.
Date: January 1, 1978
Creator: Hartman, F. C.; Norton, I. L.; Stringer, C. D. & Schloss, J. V.
Partner: UNT Libraries Government Documents Department

Carotenoid biosynthesis in bacteria: In vitro studies of a crt/bch transcription factor from Rhodobacter capsulatus and carotenoid enzymes from Erwinia herbicola

Description: A putative transcription factor in Rhodobactor capsulatus which binds upstream of the crt and bch pigment biosynthesis operons and appears to play a role in the adaptation of the organism from the aerobic to the anaerobic-photosynthetic growth mode was characterized. Chapter 2 describes the identification of this factor through an in vitro mobility shift assay, as well as the determination of its binding properties and sequence specificity. Chapter 3 focuses on the isolation of this factor. Biochemistry of later carotenoid biosynthesis enzymes derived from the non-photosynthetic bacterium, Erwinia herbicola. Chapter 4 describes the separate overexpression and in vitro analysis of two enzymes involved in the main sequence of the carotenoid biosynthesis pathway, lycopene cyclase and 5-carotene hydroxylase. Chapter 5 examines the overexpression and enzymology of functionally active zeaxanthin glucosyltransferase, an enzyme which carries out a more unusual transformation, converting a carotenoid into its more hydrophilic mono- and diglucoside derivatives. In addition, amino acid homology with other glucosyltransferases suggests a putative binding site for the UDP-activated glucose substrate.
Date: November 1, 1992
Creator: O'Brien, D.A.
Partner: UNT Libraries Government Documents Department

Carbonic anhydrase levels and internal lacunar CO/sub 2/ concentrations in aquatic macrophytes

Description: Carbonic anhydrase levels were examined in a variety of aquatic macrophytes from different habitats. In general, carbonic anhydrase levels increased across the habitat gradient such that activities were low in submersed aquatic macrophytes and high in emergent macrophytes with floating-leaved and free-floating plants exhibiting intermediate activities. Internal lacunar CO/sub 2/ concentrations were analyzed in relation to carbonic anhydrase activities. There was no correlation between these two parameters. Internal CO/sub 2/ concentrations ranged from low to high in submersed macrophytes, but were low in floating-leaved and emergent macrophytes. The observed internal CO/sub 2/ concentrations are discussed in relation to the individual morphologies of the plants and the environments in which they occurred.
Date: January 1, 1979
Creator: Weaver, C.I.
Partner: UNT Libraries Government Documents Department

[Regulation of terpene metabolism]

Description: This report describes accomplishments over the past year on understanding of terpene synthesis in mint plants and sage. Specifically reported are the fractionation of 4-S-limonene synthetase, the enzyme responsible for the first committed step to monoterpene synthesis, along with isolation of the corresponding RNA and DNA cloning of its gene; the localization of the enzyme within the oil glands, regulation of transcription and translation of the synthetase, the pathway to camphor biosynthesis,a nd studies on the early stages and branch points of the isoprenoid pathway.
Date: January 1, 1992
Creator: Croteau, R.
Partner: UNT Libraries Government Documents Department