THE FIXATION OF CARBON DIOXIDE IN A PLANT TRICARBOXYLIC ACID SYSTEM

1. The pathway of ethanol metabolism in cotyledons of 3-day-old pea seedlings has been examined by incubating tissue slices with [1−14C]ethanol and [2−14C]ethanol for periods up to 1hr. 2. Ethanol was rapidly incorporated into citrate and glutamate but relatively small amounts of 14C were present in the evolved carbon dioxide even after 1hr. of ethanol metabolism. 3. Similar data were obtained from experiments in which [1,2−14C2]acetaldehyde and [14C]acetate were supplied. 4. The results are interpreted as indicating that ethanol is metabolized essentially via the reactions of the tricarboxylic acid cycle with a substantial drain of α-oxoglutarate to support the biosynthesis of glutamate. 5. It is concluded that oxaloacetate, required for the incorporation of ethanol into citrate, arises mainly from the transamination of aspartate and the fixation of carbon dioxide.

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Studies of the Fixation of Carbon Dioxide by Washed Ram Spermatozoa

Australian Journal of Biological Sciences ◽

10.1071/bi9700889 ◽

1970 ◽

Vol 23 (4) ◽

pp. 889 ◽

Cited By ~ 2

Author(s):

T O'shea ◽

RG Wales

Keyword(s):

Carbon Dioxide ◽

Substrate Concentration ◽

Tricarboxylic Acid Cycle ◽

Tricarboxylic Acid ◽

Acid Cycle ◽

Tricarboxylic Acid Cycle Intermediates ◽

Fixation Of Carbon Dioxide

Fixation of carbon dioxide by ram spermatozoa was studied by incubating washed cells with NaH14C03? More fixation of carbon dioxide occurred as the substrate concentration was increased, and was very low in the absence of added substrate. Less incorporation occurred with acetate than with pyruvate or lactate. A marked increase in fixation was seen when ketoglutarate or malate replaced portion of the lactate in the medium, but not when other tricarboxylic acid cycle intermediates were substituted. Fixation of carbon dioxide was higher when ketoglutarate plus malate rather than when either substrate alone partially replaced lactate.

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Atom Condensed Fukui Function for Condensed Phases and Biological Systems and Its Application to Enzymatic Fixation of Carbon Dioxide

10.26434/chemrxiv.9198770.v2 ◽

2019 ◽

Author(s):

Javier Oller ◽

David A. Sáez ◽

Esteban Vöhringer-Martinez

Keyword(s):

Carbon Dioxide ◽

Aqueous Solution ◽

Molecular System ◽

Chemical Reactivity ◽

Nucleophilic Attack ◽

Stable Conformation ◽

Fukui Functions ◽

Reactivity Descriptors ◽

Dynamics Simulations ◽

Fixation Of Carbon Dioxide

<div><div><div><p>Local reactivity descriptors such as atom condensed Fukui functions are promising computational tools to study chemical reactivity at specific sites within a molecule. Their applications have been mainly focused on isolated molecules in their most stable conformation without considering the effects of the surroundings. Here, we propose to combine QM/MM Born-Oppenheimer molecular dynamics simulations to obtain the microstates (configurations) of a molecular system using different representations of the molecular environment and calculate Boltzmann weighted atom condensed local reac- tivity descriptors based on conceptual DFT. Our approach takes the conformational fluctuations of the molecular system and the polarization of its electron density by the environment into account allowing us to analyze the effect of changes in the molecular environment on reactivity. In this contribution, we apply the method mentioned above to the catalytic fixation of carbon dioxide by crotonyl-CoA carboxylase/reductase and study if the enzyme alters the reactivity of its substrate compared to an aqueous solution. Our main result is that the protein en- vironment activates the substrate by the elimination of solute-solvent hydrogen bonds from aqueous solution in the two elementary steps of the reaction mechanism: the nucleophilic attack of a hydride anion from NADPH on the α, β unsaturated thioester and the electrophilic attack of carbon dioxide on the formed enolate species.</p></div></div></div>

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