Glycolate pathway inhibition

Radioactive isoprene was liberated from leaf surfaces of Hamamelis virginiana and Quercus borealis when labelled intermediates of the glycolate pathway and labelled mevalonate were fed to them.55 It is not clear whether MVA was an obligate precursor of isoprene, although inhibition studies showed a distinct similarity between the biosynthetic pathway to isoprene and that to /3-carotene. 

Successful fusion (2) is a rare event, but the frequency can be improved by adding polyethylene glycol (PEG). To obtain only successfully fused cells, incubation is required for an extended period in a primary culture with HAT medium (3), which contains hypoxan-thine, aminopterin, and thymidine. Amino-pterin, an analogue of dihydrofolic acid, competitively inhibits dihydrofolate reductase and thus inhibits the synthesis of dTMP (see p. 402). As dTMP is essential for DNA synthesis, myeloma cells cannot survive in the presence of aminopterin. Although spleen cells are able to circumvent the inhibitory effect of aminopterin by using hypoxanthine and thymidine, they have a limited lifespan and die. Only hybridomas survive culture in HAT medium, because they possess both the immortality of the myeloma cells and the spleen cells metabolic side pathway. 

The combined activity of the rubisco oxygenase and the glycolate salvage pathway consumes 02 and produces C02—hence the name photorespiration. This pathway is perhaps better called the oxidative photosynthetic carbon cycle or C2 cycle, names that do not invite comparison with respiration in mitochondria. Unlike mitochondrial respiration, photorespiration does not conserve energy and may actually inhibit net biomass formation as much as 50%. This inefficiency has led to evolutionary adaptations in the carbon-assimilation processes, particularly in plants that have evolved in warm climates. 

Treatment of ethylene glycol poisoning. The metabolic pathway shown across the top of the figure illustrates the conversion of ethylene glycol to oxalic acid. This can be inhibited by the action of the competitive inhibitor, ethanol, shown in purple. 

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