PubMed · 4711243
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
G W Gribble. 1973. Fluoroacetate toxicity.. https://doi.org/10.1021/ed050p460
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Scenarios for driving the Krebs cycle in reverse in the absence of enzymatic networks have received much attention in the literature of prebiotic evolution because repeated cycling provides a core mechanism for the synthesis of useful biomolecules from carbon dioxide. Here, we show that three of the five reductive steps in the cycle can be driven photochemically at high yield by a ZnS colloid. The results show the conversion of oxaloacetate to malate, fumarate to succinate, and oxoglutarate to oxalosuccinate. The experimental conditions of circumneutral pH and 288 K, as well as the ZnS semiconductor photocatalyst particles (sphalerite), are believed to have been prevalent in the waters of early Earth. These findings therefore both establish and constrain the plausibility of the occurrence of heretofore difficult chemical conversions in prebiotic metabolic systems.
The likelihood of a functioning nonenzymatic reductive citric acid cycle, recently proposed as the precursor to biosynthesis on early Earth, is examined on the basis of the kinetics and thermochemistry of the acetate --> pyruvate --> oxaloacetate --> malate sequence. Using data derived from studies of the Pd-catalyzed phosphinate reduction of carbonyl functions it is shown that the rate of conversion of pyruvate to malate with that system would have been much too slow to have played a role in the early chemistry of life, while naturally occurring reduction systems such as the fayalite-magnetite-quartz and pyrrhotite-pyrite-magnetite mineral assemblages would have provided even slower conversions. It is also shown that the production of pyruvate from acetate is too highly endoergic to be driven by a naturally occurring energy source such as pyrophosphate. It is thus highly doubtful that the cycle can operate at suitable rates without enzymes, and most unlikely that it could have participated in the chemistry leading to life.
In glutamate fermentations by Corynebacterium glutamicum, higher glutamate concentration could be achieved by constantly controlling dissolved oxygen concentration (DO) at a lower level; however, by-product lactate also severely accumulated. The results of analyzing activities changes of the two key enzymes, glutamate and lactate dehydrogenases involved with the fermentation, and the entire metabolic network flux analysis showed that the lactate overproduction was because the metabolic flux in TCA cycle was too low to balance the glucose glycolysis rate. As a result, the respiratory quotient (RQ) adaptive control based "balanced metabolic control" (BMC) strategy was proposed and used to regulate the TCA metabolic flux rate at an appropriate level to achieve the metabolic balance among glycolysis, glutamate synthesis, and TCA metabolic flux. Compared with the best results of various DO constant controls, the BMC strategy increased the maximal glutamate concentration by about 15% and almost completely repressed the lactate accumulation with competitively high glutamate productivity.