“…15 N-D,Lalanine was derivatized and used as a standard for GC-MS analyses. 15 Burris (21) were removed by storage over versine (22). The ammonium was collected from assays by microdiffusion and analyzed for 15 N content by R. H. Burris at the University of Wisconsin by using isotope ratio mass spectrometry.…”
Symbiotic nitrogen fixation, the process whereby nitrogen-fixing bacteria enter into associations with plants, provides the major source of nitrogen for the biosphere. Nitrogenase, a bacterial enzyme, catalyzes the reduction of atmospheric dinitrogen to ammonium. In rhizobialeguminous plant symbioses, the current model of nitrogen transfer from the symbiotic form of the bacteria, called a bacteroid, to the plant is that nitrogenase-generated ammonia diffuses across the bacteroid membrane and is assimilated into amino acids outside of the bacteroid. We purified soybean nodule bacteroids by a procedure that removed contaminating plant proteins and found that alanine was the major nitrogencontaining compound excreted. Bacteroids incubated in the presence of 15 N 2 excreted alanine highly enriched in 15 N. The ammonium in these assays neither accumulated significantly nor was enriched in 15 N. The results demonstrate that a transport mechanism rather than diffusion functions at this critical step of nitrogen transfer from the bacteroids to the plant host. Alanine may serve only as a transport species, but this would permit physiological separation of the transport of fixed nitrogen from other nitrogen metabolic functions commonly mediated through glutamate.In 1956 (1), ammonium was shown to be the product of nitrogenase, the bacterial enzyme that reduces atmospheric dinitrogen. In free-living, nitrogen-fixing microorganisms, the nitrogenase-generated ammonium is assimilated into glutamate through the glutamine synthetase͞glutamate synthase pathway. Various transaminases utilize glutamate to generate all of the other amino acids, which are then used to synthesize proteins, nucleic acids and other nitrogen-containing molecules.In rhizobia-leguminous plant symbioses, the majority of the dinitrogen reduced by the microsymbionts, referred to as bacteroids, is transferred to the plant. Because the rhizobia are physically separated from the plant cytosol by a plant-derived symbiosome membrane, the ammonium must move across the bacteroid and symbiosome membranes. The ammonia diffusion hypothesis has been the prevalent model surmising the initial steps of leguminous nodule nitrogen transfer. In this model, the product of nitrogenase exists in two forms within the cell, ammonium [NH 4 ϩ ] and ammonia [NH 3 ], which are readily interconvertible. The ammonium ion cannot diffuse across membranes, but ammonia is believed to diffuse freely out of the bacteroid. Once outside the bacteroid but within the symbiosome space, the ammonia may either diffuse or be transported across the symbiosome membrane (2) where it is assimilated by the host plant into glutamate by the concerted action of glutamine synthetase and glutamate synthase. Glutamate serves as the central nitrogen metabolite in the plant nodule cells for the synthesis of the other amino acids, nucleic acids, and other nitrogen-containing compounds such as ureides that are the principal nitrogen compounds transported from the nodules to the plant shoots and leaves o...
“…15 N-D,Lalanine was derivatized and used as a standard for GC-MS analyses. 15 Burris (21) were removed by storage over versine (22). The ammonium was collected from assays by microdiffusion and analyzed for 15 N content by R. H. Burris at the University of Wisconsin by using isotope ratio mass spectrometry.…”
Symbiotic nitrogen fixation, the process whereby nitrogen-fixing bacteria enter into associations with plants, provides the major source of nitrogen for the biosphere. Nitrogenase, a bacterial enzyme, catalyzes the reduction of atmospheric dinitrogen to ammonium. In rhizobialeguminous plant symbioses, the current model of nitrogen transfer from the symbiotic form of the bacteria, called a bacteroid, to the plant is that nitrogenase-generated ammonia diffuses across the bacteroid membrane and is assimilated into amino acids outside of the bacteroid. We purified soybean nodule bacteroids by a procedure that removed contaminating plant proteins and found that alanine was the major nitrogencontaining compound excreted. Bacteroids incubated in the presence of 15 N 2 excreted alanine highly enriched in 15 N. The ammonium in these assays neither accumulated significantly nor was enriched in 15 N. The results demonstrate that a transport mechanism rather than diffusion functions at this critical step of nitrogen transfer from the bacteroids to the plant host. Alanine may serve only as a transport species, but this would permit physiological separation of the transport of fixed nitrogen from other nitrogen metabolic functions commonly mediated through glutamate.In 1956 (1), ammonium was shown to be the product of nitrogenase, the bacterial enzyme that reduces atmospheric dinitrogen. In free-living, nitrogen-fixing microorganisms, the nitrogenase-generated ammonium is assimilated into glutamate through the glutamine synthetase͞glutamate synthase pathway. Various transaminases utilize glutamate to generate all of the other amino acids, which are then used to synthesize proteins, nucleic acids and other nitrogen-containing molecules.In rhizobia-leguminous plant symbioses, the majority of the dinitrogen reduced by the microsymbionts, referred to as bacteroids, is transferred to the plant. Because the rhizobia are physically separated from the plant cytosol by a plant-derived symbiosome membrane, the ammonium must move across the bacteroid and symbiosome membranes. The ammonia diffusion hypothesis has been the prevalent model surmising the initial steps of leguminous nodule nitrogen transfer. In this model, the product of nitrogenase exists in two forms within the cell, ammonium [NH 4 ϩ ] and ammonia [NH 3 ], which are readily interconvertible. The ammonium ion cannot diffuse across membranes, but ammonia is believed to diffuse freely out of the bacteroid. Once outside the bacteroid but within the symbiosome space, the ammonia may either diffuse or be transported across the symbiosome membrane (2) where it is assimilated by the host plant into glutamate by the concerted action of glutamine synthetase and glutamate synthase. Glutamate serves as the central nitrogen metabolite in the plant nodule cells for the synthesis of the other amino acids, nucleic acids, and other nitrogen-containing compounds such as ureides that are the principal nitrogen compounds transported from the nodules to the plant shoots and leaves o...
“…CO is also capable of fueling various metabolic processes, such as acetogenesis, methanogenesis, hydrogenogenesis, and aerobic carboxydotrophy (Fig. 4 ) (Pugh and Umbreit 1966 ; Ragsdale and Pierce 2008 ; Diender et al 2015 ; Jones et al 2016 ; Robb and Techtmann 2018 ). Fig.…”
Anthropogenic carbon dioxide (CO2) levels are rising to alarming concentrations in earth’s atmosphere, causing adverse effects and global climate changes. In the last century, innovative research on CO2 reduction using chemical, photochemical, electrochemical and enzymatic approaches has been addressed. In particular, natural CO2 conversion serves as a model for many processes and extensive studies on microbes and enzymes regarding redox reactions involving CO2 have already been conducted. In this review we focus on the enzymatic conversion of CO2 to carbon monoxide (CO) as the chemical conversion downstream of CO production render CO particularly attractive as a key intermediate. We briefly discuss the different currently known natural autotrophic CO2 fixation pathways, focusing on the reversible reaction of CO2, two electrons and protons to CO and water, catalyzed by carbon monoxide dehydrogenases (CODHs). We then move on to classify the different type of CODHs, involved catalyzed chemical reactions and coupled metabolisms. Finally, we discuss applications of CODH enzymes in photochemical and electrochemical cells to harness CO2 from the environment transforming it into commodity chemicals.
“…Na36Cl was purchased from Amersham-Searle Corp. (Canada) at a specific activity of 0.22 to 0.40 mCi/mmol, and solutions were made to the desired molarity by the addition of was from Matheson, Coleman and Bell (Norwood, Ohio). Oxygen-free grade nitrogen was purchased from Canadian Oxygen Ltd. (Kingston, Ontario), and passage through the riboflavin and methylene blue indicator solution of Pugh and Umbreit (22) showed it contained less than 50 ppm oxygen. All other chemicals were of analytical grade.…”
The uptake of Cl-by the ascomycete Neocosmospora vasinfecta was investigated. Intramycelial concentrations of more than 55 mM (890-fold the external concentration) were reached. Accumulation was as inorganic Cland nystatin induced total loss of mycelial Clwithout extensive protein loss, implying that Clretention was not due to binding to macromolecules. Cltransport was largely unidirectional with efflux being low under all conditions. Uptake was temperature dependent (maximal Arrhenius activation energy of 18.0 kcal/mol) and was severely reduced by KCN, dicyclohexylcarbodiimide, and anaerobiosis. A comparison with the inhibition of oxygen uptake under the same conditions implied that Cltransport was not directly coupled to aerobic electron transport. Cluptake was a saturatable function of the external Clconcentration, and apparent Km values of 6.4 x 10-6 M and 10-1 M were calculated. Of the anions tested, only Br-effectively inhibited Cluptake and I-, NO,-, SO,-2, HCO3-, and H2PO-4 were without effect. Cluptake did not require concomitant cation uptake.
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