Metabolism of monofluorobenzoates by Acinetobacter calcoaceticus N.C.I.B. 8250 formation of monofluorocatechols

None of the monofluorobenzoates serves as sole source of carbon and energy for growth of Acinetobacter calcoaceticus but all can contribute to growth on other substrates. The monofluorobenzoates are oxidised by bacteria pre-induced for benzoate oxidation and can themselves induce the appropriate enzymes. The initial products of oxidation have been separated and identified by gas-liquid chromatography. 2-Fluorobenzoate is oxidised to catechol, fluoride and 3-fluorocatechol; 3-fluorobenzoate gives 3- and 4-fluorocatechol; 4-fluorobenzoate gives 4-fluorocatechol. The fluorocatechols appear to be partially oxidised beyond the stage of 3-oxoadipate by suitably pre-induced bacteria

Diurnal changes in the properties of phosphoenolpyruvate carboxylase in Bryophyllum leaves: a possible co valent modification

In plants that show Crassulacean acid metabolism, phosphoenolpyruvate carboxylase catalyses the key step of CO2 fixation at night. We show here that the properties of this enzyme from Bryophyllum fedtschenkoi undergo marked changes between night and day; the night form is much less sensitive to feedback inhibition by malate than is the day form. Incubation of leaves with 32Pi followed by extraction and immunoprecipitation of phosphoenolpyruvate carboxylase showed that only the night form contained 32P. This suggests that the activity of the enzyme is controlled by a covalent modification mechanism

Persistent circadian rhythms in the phosphorylation state of phosphoenolpyruvate carboxylase from Bryophyllum fedtschenkoi leaves and in its sensitivity to inhibition by malate

Phosphoenolpyruvate carboxylase (EC 4.1.1.31; PEPCase) from Bryophyllum fedtschenkoi leaves has previously been shown to exist in two forms in vivo. During the night the enzyme is phosphorylated and relatively insensitive to feedback inhibition by malate whereas during the day the enzyme is dephosphorylated and more sensitive to inhibition by malate. These properties of PEPCase have now been investigated in leaves maintained under constant conditions of temperature and lighting. When leaves were maintained in continuous darkness and CO2-free air at 15°C, PEPCase exhibited a persistent circadian rhythm of interconversion between the two forms. There was a good correlation between periods during which the leaves were fixing respiratory CO2 and periods during which PEPCase was in the form normally observed at night. When leaves were maintained in continuous light and normal air at 15°C, starting at the end of a night or the end of a day, a circadian rhythm of net uptake of CO2 was observed. Only when these constant conditions were applied at the end of a day was a circadian rhythm of interconversions between the two forms of PEPCase observed and the rhythms of enzyme interconversion and CO2 uptake did not correlate in phase or period

Bryophyllum fedtschenkoi protein phosphatase type 2A can dephosphorylate phosphoenolpyruvate carboxylase

Phosphoenolpyruvate carboxylase, which catalyses the nocturnal fixation of CO2 in Crassulacean acid metabolism (CAM) plants, is regulated by reversible phosphorylation. The phosphorylated ‘night’ form of the enzyme is ten‐fold less sensitive to inhibition by malate than is the dephosphorylated ‘day’ form. The phosphoenolpyruvate carboxylase of the CAM plant Bryophyllum fedtschenkoi can be dephosphorylated by rabbit muscle protein phosphatase type 2A but not by type 1. B. fedtschenkoi leaves contain protein phosphatase activity that can dephosphorylate phosphoenolpyruvate carboxylase. Inhibitor studies show that this enzyme is a type 2A protein phosphatase