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Biomedical subjects

B B Buchanan

Publications and source records attributed to B B Buchanan.

At least 91 records · Page 5Linked to original sources
PubMed1978

Activation of Chloroplast NADP-linked Glyceraldehyde-3-Phosphate Dehydrogenase by the Ferredoxin/Thioredoxin System.

NADP-glyceraldehyde-3-P dehydrogenase of spinach (Spinacia oleracea) chloroplasts was activated by thioredoxin that was reduced either photochemically with ferredoxin and ferredoxin-thioredoxin reductase or chemically with dithiothreitol. The activation process that was observed with the soluble protein fraction from chloroplasts and with the purified regulatory form of the enzyme was slow relative to the rate of catalysis. The NAD-linked glyceraldehyde-3-P dehydrogenase activity that is also present in chloroplasts and in the purified enzyme preparation was not affected by reduced thioredoxin.When activated by dithiothreitol-reduced thioredoxin, the regulatory form of NADP-glyceraldehyde-3-P dehydrogenase was partly deactivated by oxidized glutathione. The enzyme activated by photochemically reduced thioredoxin was not appreciably affected by oxidized glutathione. The results suggest that although it resembles other regulatory enzymes in its requirements for light-dependent activation by the ferredoxin/thioredoxin system, NADP-glyceraldehyde-3-P dehydrogenase differs in its mode of deactivation and in its capacity for activation by enzyme effectors independently of thioredoxin.

Journal Article↗
PubMed1977

Mechanisms of CO2 fixation in bacterial photosynthesis studied by the carbon isotope fractionation technique.

The carbon isotope discrimination properties of a representative of each of the three types of photosynthetic bacteria Chlorobium thiosulfatophilum, Rhodospirillum rubrum and Chromatium and of the C3-alga Chlamydomonas reinhardii were determined by measuring the ratio of 13CO2 to 12CO2 incorporated during photoautotrophic growth. 2. Chromatium and R. rubrum had isotope selection properties similar to those of C3-plants, whereas Chlorobium was significantly different. 3. The results suggest that Chromatium and R. rubrum assimilate CO2 mainly via ribulose 1,5-diphosphate carboxylase and the associated reactions of the reductive pentose phosphate cycle, whereas Chlorobium utilizes other mechanisms. Such mechanisms would include the ferredoxin-linked carboxylation enzymes and associated reactions of the reductive carboxylic acid cycle.

Carbon Dioxide↗
PubMed1976

Studies on the regulation of chloroplast NADP-linked glyceraldehyde-3-phosphate dehydrogenase.

Chloroplast NADP-linked glyceraldehyde-3-phosphate dehydrogenase was resolved into three forms that differed in molecular weight: (a) larger than or equal to 1.5 million; (b) 600,000; and (c) less than or equal to 100,000. After preincubation with an effector (ATP, NADPH, or Pi) the activity of forms a and c was unaffected, whereas the activity of b, the regulatory form, was increased 10-fold. Activation was accompanied by the exposure of previously hidden sulfhydryl groups. The rate of activation was slower than the rate of catalysis and resulted in a lag phase during the measurement of activity when the enzyme was preincubated in the absence of an effector. The addition of one of several compounds as a second effector (at a concentration which itself was nonactivating) in the presence of a first effector enhanced activation by lowering the concentration of the first effector required for half-maximal activation (Pi constant/ATP or NADPH varied; ATP or NADPH constant/Pi varied). Other combinations of effectors caused little change in activity (ATP constant/NADPH varied; NADPH constant/ATP varied). Glyceraldehyde 3-phosphate added as a second effector induced contrasting changes: an increase in the ATP-mediated activation and a decrease in the NADPH-mediated activation. The results are consistent with the view that the products of the photochemical reactions of chloroplasts, ATP, and NADPH, in conjunction with other metabolites, regulate the activity of glyceraldehyde-3-phosphate dehydrogenase in the photosynthetic assimilation of CO2.

Adenosine Triphosphate↗
PubMed1976

Ribulose 1,5-diphosphate carboxylase and Cholorobium thiosulfatophilum.

1. Cell-free extracts of the photosynthetic bacterium Cholorobium thiosulfatophilum, strains 8327 and Tassajara, were assayed for ribulose 1,5-diphosphate (RuDP) carboxylase and phosphoribulokinase--the two enzymes peculiar to the reductive pentose phosphate cycle. 2. RuDP carboxylase was consistently absent in strain 8327. The Tassajara strain showed a low RuDP-dependent CO2 fixation activity that was somewhat higher in cells following transatlantic air shipment than in freshly grown cells. The stability and behaviour of this activity in sucrose density gradients were similar to those described by other workers. 3. The radioactive carboxylation products formed in the presence of RuDP by enzyme preparations from the Tassajara strain did not include 3-phosphoglycerate--the known product of the RuDP carboxylase reaction, but instead consisted of the unrelated acids glutamate, aspartate and malate. 4. Phosphoribulokinase was absent in all preparations of the two Chlorobium strains tested. By contrast, phosphoribulokinase as well as RuDP carboxylase were readily demonstrated in preparations from pea chloroplasts and the photosynthetic bacterium Rhodospirillum rubrum. 5. It is concluded that C. thiosulfatophilum appears to lack RuDP carboxylase, phosphoribulokinase, and hence, the reductive pentose phosphate cycle.

Carbon Dioxide↗
PubMed1976

Antibody evidence for different conformational states of ADP, ATP translocator protein isolated from mitochondria.

Consistent with the previously proposed reorientation mechanism for the ADP,ATP translocator protein of mitochondria, evidence has now been obtained for the existence of two distinct conformational states of the isolated translocator protein. Previous studies indicated that when the mitochondrial translocator protein is in the c-state(i.e., when its binding site faces the cytosol side) the protein binds primarily the ligand carboxyatractylate (CAT), and when the translocator protein is in the m-state(i.e., when its binding site faces the mitochondrial matrix) the translocator protein binds primarily bongkrekate. Direct evidence for this formulation has now come from the application of antibodies to the isolated translocator protein-ligand complex. Two antibodies were produced against the ADP,ATP translocator protein isolated from beef heart mitochondria. One antibody, which was produced against the protein isolated as the CAT-binding protein complex, was found to be highly specific for that complex and did not react with the protein in the conformation state conferred by the bongkrekate ligand. This antibody did not cover the CAT-binding site, as evidenced by the exchange of unlabeled CAT with [35S]CAT bound to the translocator protein. However, the same antibody inhibited a transition of the protein from the c-state to the m-state, as evidenced by an inhibition of the displacement of[35S]CAT by bongkrekate (added jointly with ADP). It appears, therefore, that the antibody immobilized the translocator protein in the c-state. The second antibody produced against the (somewhat less pure) ADP,ATP translocator protein, isolated as the bongkrekate-binding protein complex, did not react with the CAT-binding protein. Thus, the second antibody appeared to be specific for the translocator protein in the m-state. Neither antibody inhibited mitochondrial ADP,ATP transport.

Adenosine Diphosphate↗
PubMed1976

Effect of powdery mildew infection on photosynthesis by leaves and chloroplasts of sugar beets.

Chloroplasts isolated from powdery mildew-infected (Erysiphe polygoni DC) sugar beet leaves (Beta vulgaris L) showed a reduction in the rate of electron transport and in the accompanying ATP formation in noncyclic photophosphorylation (water as electron donor, NADP as electron acceptor) and little or no change in the rate of ATP formation in cyclic photophosphorylation catalyzed by phenazine methosulfate. The inhibition of noncyclic photophosphorylation appeared to lead in the parent leaves to a decreased rate of photosynthetic CO(2) assimilation and a shift in products resulting in a relative increase of amino acids. These changes were accompanied by alterations in chloroplast ultrastructure and by a reduction in the activity of enzymes necessary for the formation of organic acids (phosphoenolpyruvate carboxylase and malate dehydrogenase). These results are similar to the findings of Montalbini and Buchanan (1974 Physiol. Plant Pathol. 4: 191-196) with chloroplasts from rust-infected Vicia faba leaves.

Journal Article↗
PubMed1975

Cytochrome b and photosynthetic sulfur bacteria.

Chromatophores isolated from the purple sulfur bacterium Chromatium and the green sulfur bacterium Chlorobium exhibit absorbance changes in the cytochrome alpha-band region consistent with the presence of a b-type cytochrome. Cytochrome content determined by reduced minus oxidized difference spectra and by heme photochemically active bacteriochlorophyll (reaction-center bacteriochlorophyll). The b-type cytochrome in Chromatium has an alpha-band maximum at 560 nm and a midpoint oxidation-reduction potential of -5 mV at pH 8.0. The b-type cytochrome in Chlorobium has an alpha-band maximum at 564 nm and an apparent midpoint oxidation-reduction potential near -90 mV. Chromatophores isolated from both Chromatium and Chlorobium cells catalyze a photoreduction of cytochrome b that is enhanced in the presence of antimycin A. Antimycin A and 2-n-heptyl-4-hydroxyquinoline-N-oxide inhibit endogenous (but not phenazine methosulfate-mediated) cyclic photophosphorylation in Chromatium chromatophores and non-cyclic electron flow from Na-2S to NADP in Chlorobium chromatophores. These observations suggest that b-type cytochromes may function in electron transport reactions in photosynthetic sulfur bacteria.

Antimycin A↗