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D J Oliver

Publications and source records attributed to D J Oliver.

At least 55 records · Page 3Linked to original sources
PubMed1986

Glycine decarboxylase multienzyme complex. Purification and partial characterization from pea leaf mitochondria.

The P, H, and T proteins of the glycine cleavage system have been purified separately from pea leaf mitochondria and demonstrate molecular weights of 98,000, 15,500, and 45,000, respectively, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular weight of P protein by gel filtration was 210,000, indicating that this enzyme has a native homodimer conformation. Reconstitution assays containing purified P, H, and T proteins and yeast lipoamide dehydrogenase catalyze the oxidation of glycine and demonstrate a strict dependence on pyridoxal phosphate, tetrahydrofolate, NAD+, and dithiothreitol. The released CO2, methylamine-H protein intermediate, and methylenetetrahydrofolate are produced in stoichiometric amounts from glycine during the cleavage reaction. H protein acts as co-substrate with glycine during the decarboxylation reaction, demonstrating an apparent Km value of 2.2 microM. P and H protein alone jointly catalyze the glycine carboxyl-14 CO2 exchange reaction in the presence of pyridoxal phosphate and dithiothreitol. L protein of the glycine cleavage system was immunopurified using monoclonal antibodies. Antigenic and molecular weight similarities of the L protein with the lipoamide dehydrogenase component of the pyruvate dehydrogenase complex were shown suggesting the possibility of common isomers of lipoamide dehydrogenase for the two enzyme complexes.

Amino Acid Oxidoreductases↗
PubMed1985

Medical management of intestinal obstruction in patients with advanced malignant disease. A clinical and pathological study.

A clinical and pathological study was made of 40 patients with intestinal obstruction due to far-advanced abdominal and/or pelvic malignant disease. Surgical intervention was feasible in only 2 cases. The remaining 38 patients were managed medically without intravenous fluids and nasogastric suction. Obstructive symptoms such as intestinal colic, vomiting, and diarrhoea were effectively controlled by drugs.

Abdominal Neoplasms↗
PubMed1985

Inhibition of glycine oxidation by carboxymethoxylamine, methoxylamine, and acethydrazide.

Carboxymethoxylamine (amino-oxyacetate), methoxylamine, and acethydrazide are shown to be effective, although not completely specific, inhibitors of glycine oxidation by the isolated glycine decarboxylase multienzyme complex, mitochondria, protoplasts, and leaf discs from peas. The inhibition probably results from a reaction between these compounds and the pyridoxal 5-phosphate cofactor of the enzyme.

Journal Article↗
PubMed1984

Characterization of the transport of oxaloacetate by pea leaf mitochondria.

Mitochondria isolated from pea (Pisum sativum L.) leaves are able to transport the keto acid, oxaloacetate, from the reaction medium into he mitochondrial matrix at high rates. The rate of uptake by the mitochondria was measured as the rate of disappearance of oxaloacetate from the reaction medium as it was reduced by matrix malate dehydrogenase using NADH provided by glycine oxidation. The oxaloacetate transporter was identifed as being distinct from the dicarboxylate and the alpha-ketoglutarate transporters because of its inhibitor sensitivities and its inability to interact with other potential substrates. Phthalonate and phthalate were competitive inhibitors of oxaloacetate transport with K(i) values of 60 micromolar and 2 millimolar, respectively. Butylmalonate, an inhibitor of the dicarboxylate and alpha-ketoglutarate transporters, did not alter the rate of oxaloacetate transport. In addition, a 1000-fold excess of malate, malonate, succinate, alpha-ketoglutarate, or phosphate had little effect on the rate of oxaloacetate transport. The K(m) for the oxaloacetate transporter was about 15 micromolar with a maximum velocity of over 500 nanomoles per milligram mitochondrial protein/min at 25 degrees C. No requirement for a counter ion to move against oxaloacetate was detected and the highest rates of uptake occurred at alkaline pH values. An equivalent transporter has not been reported in animal mitochondria.

Journal Article↗
PubMed1983

Changes in the electron transport chain of pea leaf mitochondria metabolizing malate.

Pea leaf mitochondria showed complex kinetics for malate metabolism. O2 uptake increased as malate concentration increased from 0 to 10 mM, reached a plateau between 10 and 20 mM malate, and then increased again up to 40 mM malate. Analysis of the products of malate oxidation by high-performance liquid chromatography revealed that the first phase of O2 uptake coincided with the synthesis of both pyruvate and oxalacetate (OAA) while the second phase of O2 uptake at higher malate levels usually occurred with a large increase in OAA formation. The biphasic response in O2 uptake and the changing ratios of pyruvate and OAA synthesis did not appear to be the direct result of the differing Km values of malate dehydrogenase and malic enzyme. Rather, they resulted from thermodynamic properties of these two malate oxidases and the kinetics of the two NADH dehydrogenases found in plant mitochondria. At low malate concentrations the rotenone-sensitive NADH dehydrogenase was active and could accept electrons from both malate oxidases. This NADH dehydrogenase became saturated at about 10 mM malate. At higher malate concentrations the rotenone-insensitive NADH dehydrogenase was increasingly important and its increased electron transport capacity was best exploited by malate dehydrogenase. At the higher malate concentrations an increasing portion of the electrons from malate reduce O2 through the alternative oxidase. Although this coincided with the second phase of malate-dependent O2 uptake it was not required for this phase to be seen.

Antimycin A↗
PubMed1983

Extraction and partial characterization of the glycine decarboxylase multienzyme complex from pea leaf mitochondria.

Glycine decarboxylase has been successfully solubilized from pea (Pisum sativum) leaf mitochondria as an acetone powder. The enzyme was dependent on added dithiothreitol and pyridoxal phosphate for maximal activity. The enzyme preparation could catalyze the exchange of CO(2) into the carboxyl carbon of glycine, the reverse of the glycine decarboxylase reaction by converting serine, NH(4) (+), and CO(2) into glycine, and (14)CO(2) release from [1-(14)C]glycine. The half-maximal concentrations for the glycine-bicarbonate exchange reaction were 1.7 millimolar glycine, 16 millimolar NaH(14)CO(2), and 0.006 millimolar pyridoxal phosphate. The enzyme (glycine-bicarbonate exchange reaction) was active in the assay conditions for 1 hour and could be stored for over 1 month. The enzymic mechanism appeared similar to that reported for the enzyme from animals and bacteria but some quantitative differences were noted. These included the tenacity of binding to the mitochondrial membrane, the concentration of pyridoxal phosphate needed for maximum activity, the requirement for dithiothreitol for maximum activity, and the total amount of activity present. Now that this enzyme has been solubilized, a more detailed understanding of this important step in photorespiration should be possible.

Journal Article↗
PubMed1982

Simultaneous oxidation of glycine and malate by pea leaf mitochondria.

Mitochondria isolated from pea leaves (Pisum sativum L.) readily oxidized malate and glycine as substrates. The addition of glycine to mitochondria oxidizing malate in state 3 diminished the rate of malate oxidation. When glycine was added to mitochondria oxidizing malate in state 4, however, the rate of malate oxidation was either unaffected or stimulated. The reason both glycine and malate can be metabolized in state 4 appears to be that malate only used part of the electron transport capacity available in these mitochondria in this state. The remaining electron transport capacity was used by glycine, thus allowing both substrates to be oxidized simultaneously. This can be explained by differential use of two NADH dehydrogenases by glycine and malate and an increase in alternate oxidase activity upon glycine addition. These results help explain why photorespiratory glycine oxidation and its associated demand for NAD do not inhibit citric acid cycle function in leaves.

Journal Article↗
PubMed1981

Formate oxidation and oxygen reduction by leaf mitochondria.

Mitochondria isolated from the leaves of several plant species were investigated for the presence of NAD-linked formate dehydrogenase. The NADH produced was oxidized by the electron transport sequence and was coupled to ATP synthesis. The amounts of formate dehydrogenase, and, thereby, the capacity for formate-dependent O(2) uptake, varied greatly among species. While no activity was detectable in mitochondria from soybean leaves, the rate of formate oxidation by spinach mitochondria was about one-half the rate of malate oxidation. In spinach, only mitochondria from green tissues oxidized formate. These last two observations raise questions as to the role of this reaction and the possible sources of the formate metabolized.

Journal Article↗
PubMed1981

Role of Glycine and Glyoxylate Decarboxylation in Photorespiratory CO(2) Release.

Mechanically isolated soybean leaf cells metabolized added glycolate by two mechanisms, the direct oxidation of glyoxylate and the decarboxylation of glycine. The rate of glyoxylate oxidation was dependent on the cellular glyoxylate concentration and was linear between 0.58 and 2.66 micromoles glyoxylate per milligram chlorophyll. The rate extrapolated to zero at a concentration of zero. The concentration and, therefore, the rate of oxidation of glyoxylate could be decreased by adding glutamate or serine to the cells. These substrates were amino donors for the transamination of glyoxylate to glycine. In the presence of these amino acids more CO(2) was released from added glycolate via the glycine decarboxylation reaction and less by the direct oxidation of glyoxylate.Leaves from soybean plants of various ages grown under different nitrogen regimes had glyoxylate concentrations of about 80 to 100 nanomoles per milligram chlorophyll. Using the isolated cells as a model to determine the relationships between the glyoxylate concentration and rate of its decarboxylation indicated that about 2.5% of the photorespiratory CO(2) would arise from this reaction. This percentage would not be expected to vary greatly with growth conditions.

Journal Article↗
PubMed1980

Functional changes in autonomic nervous responses with ageing.

The effects of ageing on autonomic nervous responses have been investigated in 29 young adults, 64 healthy elderly in the age range 66 to 86 years, and 20 elderly in-patients with hypothermia, instability of bladder function or marked orthostatic hypotension. In the healthy elderly group, the beat-to-beat variation in response to postural change was significantly diminished, the vasoconstrictor response to cooling reduced and baroreflex sensitivity during lower-body negative pressure was decreased compared with young adults. Patients with an atronic bladder, determined by urodynamic tests, showed an even more marked decrease in baroreflex sensitivity. The multisystem nature of these autonomic disturbances suggests that physiological impairment may occur in autonomic neural pathways with ageing.

Adult↗