This thesis considers theories of expansions of the natural algebraic struc- ture on the multiplicative group and on an elliptic curve by a predicate for a subgroup that are constructed by Hrushovski's predimension method. In the case of the multiplicative group, these are the theories of fields with green points constructed by Poizat. The convention of calling the elements of the distinguished subgroup green points is maintained throughout this work, also in the elliptic curve case, and we speak of theories of green points. In the first part of the thesis, we give a detailed account of the construction of the theories of green points. The work of Poizat is extended to the case of elliptic curves and an open question is answered in order to complete the construction in the cases where the distinguished subgroup is allowed to have torsion. Proofs of the main model-theoretic properties of the theories, w-stability and near model-completeness, are included, as well as rank calculations. In the second part, following ideas of Zilber, we find natural models of the constructed theories on the complex points of the corresponding algebraic group. In the case of elliptic curves, this is done under the assumption that the curve has no complex multiplication and is defined over the reals. In general, we also need to assume a consequence of the Schanuel Conjecture, in the multiplicative group case, and an analogous statement in the elliptic curve case. For the multiplicative group, the assumption is known to hold in generic cases by a theorem of Bays, Kirby and Wilkie; our result is therefore unconditional in these cases. Motivated by Zilber's work on connections between model theory and non- commutative geometry, we prove similar results for variations of the above theories in which the distinguished subgroup is elementarily equivalent to the additive group of the integers, which we call theories of emerald points.

The NET protein superfamily is a recently discovered family of novel, plant-specific actin binding proteins. The identification of this family represents a significant discovery as the plant cytoskeleton is not identical to the animal cytoskeleton and plant cells show plant specific processes and subcellular structures which rely on actin. There is a need for plant specific proteins which are capable of modelling actin within plant cells. The NET family comprises thirteen proteins in Arabidopsis thaliana, which share the NET actin binding domain (found at the N-terminal end of each protein). Based on the C-terminal domains of the proteins, the family can be separated into four groups, each with a particular localisation. The localisations of these proteins are frequently within plant specific cell types, such as pollen tubes, guard cells or roots, or to plant specific cell structures such as plasmodesmata. It is thought that these proteins may be involved in modelling the actin cytoskeleton at junctions between actin and membranes (either cell membranes or membrane bound structures such as the endoplasmic reticulum). The NET1 proteins are a group of four proteins, each consisting of an N-terminal actin binding domain and C-terminal coiled-coil domains. NET1a was the first protein to be discovered in a high-throughput screen of plant proteins for novel localisations carried out by Karl Oparka, where it was shown to bind to filaments. Work by Calcutt (Calcutt 2009) showed the filaments to be the actin cytoskeleton. The aim of this thesis has been to complete the characterisation of all Group 1 NET proteins, building on the analysis of NET1a by Calcutt (Calcutt 2009) and to investigate the possible functions of the NET1 subfamily proteins. All four proteins have been shown to be capable of actin binding and to be expressed in, and locate to structures within, the roots of A. thaliana. NET1a has been linked to plasmodesmata, and the combined absence of NET1a and NET1b in the plant results in a cumulative, long root phenotype. Theories to explain this phenotype are suggested here, although the validation and testing of these will form the basis of future work.

The widespread occurrence of a large variety of long chain fatty acids has encouraged considerable investigation into the methods by which they are biosynthesised. The overall mechanisms of many of these pathways have been elucidated, but much remains to be discovered about the absolute stereochemistry of these reactions. This thesis describes work carried out to help define the stereochemistry of some of these reactions. To investigate the stereochemistry of two of the intermediate steps of chain elongation in fatty acid biosynthesis, the synthesis of αβ-unsaturated and β-hydroxy fatty acids specifically labelled with either tritium or deuterium was undertaken. The incubation of these labelled acids with the green algae Chlorella vulgaris allowed the absolute stereospecificity of the dehydration and hydrogenation steps of acyl chain elongation to be determined.

1) Three fructofuranosidases were separated by chromatography on DEAE-cellulose columns from the soluble protein extracted from dandelion (Taraxacum officinale Weber) roots. One enzyme, which acted on sucrose, was characterized as an invertase, with a Km of 2.00x10-2M and pH optimum of 7.5. The other two enzymes are hydrolases (A and B) which act on the inulin series of carbohydrates, general formula: [glucose-fructose-(fructose)n], to release single fructose residues. They both have a pH optimum of 4.0 and Km of 1.54x10-2M but differ in their chromatographic behaviour on DEAE-cellulose, 2) Soluble protein extracts prepared from dandelion roots were able to synthesise oligosaccharides from sucrose by transfructosylation. Preliminary experiments suggest that this occurs via two enzymes; SST (pH optimum 4.5) catalysing the formation of 1F-fructosylsucrose from sucrose, the other, FFT (pHoptimum 8.5) catalyses the formation of higher oligosaccharides from 1F-fructosylsucrose. 3) Treatment of tissue disks prepared from dandelion roots with solutions of the highly active growth regulator 2, 4-dichlorophenoxyacetic acid (2,4-D) resulted in a large uptake of water. This was accompanied by an increase in hydrolase activity and depolymerization of the storage carbohydrate inulin; the free sugars released did not accumulate but were immediately utilized by the tissue. The net result was an increase in the rate of respiration and the depletion of carbohydrate reserves. The increase in hydrolase activity was inhibited by actinomycin D, indicating that the synthesis of a messenger RNA is involved. The increase in hydrolase activity was also inhibited if various sugars were included in the incubation medium. Similar treatment with the isomer 3,5-dichlorophenoxyacetic acid (3,5-D) which is inactive as an auxin, produced little or no response, and was even able to inhibit the action of 2,4-D. 4) In the summer, flowering of dandelion plants was accompanied by depletion of carbohydrate reserves present in the roots; these reserves were restored in the autumn. The variations in hydrolase and transfructosylase activities were consistent with these changes. The response of tissue disks to treatment with 2,4-D showed a similar seasonal variation to that of the initial fructosan content, suggesting that the availability of carbohydrate reserves limits the response throughout the season.

No description available.

A rapid procedure was developed for the purification and reconstitution into proteoliposomes of the tonoplast H<SUP></SUP>&43 -translocating ATPase from the Crassulacean acid metabolism (CAM) plant <i>Kalanchoédaigremontiana</i>. It involved the fractionation of crude tonoplast membranes with the detergent Triton X-114, resolubization of the ATPase with octyl glucoside in the presence of an optimized lipid mixture and formation of liposomes on removal of detergent by gel filtration. The enzyme could be further purified by sedimentation through glycerol gradients. It contained polypeptides of apparent molecular mass 72, 57, 48, 42, 39, 33 and 16 kDa; the smallest of these was labelled by [<SUP>14</SUP>C]-dicyclohexylcarbodiimide. There was no evidence for the presence of any large subunits. In these proteolipsomes, ATP hydrolysis and H<SUP></SUP>+ -translocation were measured independently, by a coupled enzyme assay and by quenching of the fluorescence of a permanent weak base, respectively. The kinetic properties of the reconstitued plant ATPase were studied in detail. Rate equations derived from theoretical models of the enzyme's behaviour were fitted to experimental data by weighted non-linear regression, using a computer program that calculated the kinetic parameters that accorded to the optimal fit. The dependence of the rate of H<SUP></SUP>+ -translocation on the concentration of MgATP was well fitted by the Michaelis equation, with the K<SUB>m</SUB> value about 30 μM. ATP could be replaced by dATP, ITP, GTP, UTP or CTP and Mg^2+ by Mn^2+ or Ca^2+ kinetic parameters for these substrates were determined. In contrast hydrolysis of MgATP showed complex kinetics which suggested either negative cooperativity between nucleotide-binding sites, or the presence of two non-interacting catalytic sites. Both the hydrolytic and the H^&43 -translocating activities of the proteoliposomes were inhibited by nitrate, though not in parallel, the latter activity being more sensitive. Both activities were inhibited in parallel by bafilomycin A_1, which did not produce complete inhibition; the bafilomycin-insensitive component had complex ATPase kinetics similar to those of the uninhibited enzyme. ADP behaved as an allosteric inhibitor of the ATPase, inducing apparent cooperativity in saturation with MgATP, together with a reduction in V_max.

No description available.

In this study, the biosynthesis of albizziine has been elucidated, and a direct precursor relationship shown to exist between uracil and albizziine. This was confirmed by the demonstration that [2-<SUP>14</SUP>C]uracil specifically labels C-5 of albizziine. It is concluded that the biosynthetic sequence involves the hydroxylation of uracil to isobarbituric acid, then amination to 5-aminouracil, followed by hydrogenation and ring-opening, to yield albizziine. 2,3-Diaminopropanoic acid was shown to be formed from albizziine by the action of β-ureidopropionase. Thus, the formation of albizziine and 2,3-diaminopropanoic acid represents a further aspect of the interfacing of pyrimidine primary and secondary metabolism through uracil. Lathyrine was shown to be catabolyzed in <I>Lathyrus tingitanus</I> to yield the non-protein amino acid 4-hydroxyhomoarginine, and it was thus confirmed that 4-hydroxyhomoarginine is a catabolite rather than a precursor of lathyrine. 2-Amino-4-carboxypyrimidine, the immediate precursor of the lathyrine ring-system, was shown to be synthesized enzymically from uracil. The relative amount of exogenously supplied uracil diverted into production of the isomeric pyrimidinyl amino acids willardiine and isowillardiine in <I>Pisum sativum</I>, and also that diverted into the production of the pyrimidine amino acid lathyrine in <I>Lathyrus tingitanus</I> was determined. Uracil was shown to have a pronounced inhibitory effect on the germination and growth of <I>Phaseolus aureus</I> and <I>Glycine max</I>. As these plants do not produce pyrimidine-derived secondary products, this observation is consistent with the view that production of such compounds is a detoxification mechanism for bioactive pyrimidines.

No description available.

No description available.