Metabolism of [14C]bicarbonate byStreptococcus lactis: the synthesis, uptake and excretion of aspartate by resting cells

SummaryResting cells ofStreptococcus lactisC10 were able to synthesize aspartic acidde novobut could not actively transport aspartic acid into the cell. Intracellular aspartate was excreted from the cell in the presence of glucose but did not exchange with any extracellular amino acids. The results indicated thatStr. lactisC10 obtains the aspartic acid it requires for growth by bicarbonate fixation instead of by the utilization of extracellular aspartic acid.

An investigation into the influence of IAA and malate on in vivo and in vitro rates of dark carbon dioxide fixation in coleoptile tissue

Etiolated Avena sativa L. cv. Victory coleoptiles were used to determine the influence of indoleacetic acid (IAA) or malate on in vivo and in vitro rates of CO2 fixation. In addition, the influence of malate on IAA-stimulated growth was investigated. Concentrations of malate which stimulate growth did not influence the in vivo rate of dark [14C]bicarbonate fixation but did inhibit in vitro phosphoenolpyruvate carboxylase (EC 4.1.1.31) activity. IAA did not influence this enzymic activity or reduce the inhibition of the enzyme by malate, and the rate of [14C]bicarbonate fixation was not measurably influenced by 20 μM IAA within the time period required for IAA stimulation of growth to become apparent. In the absence of atmospheric levels of CO2, 1 mM malate and 20 μM IAA stimulate growth in a weakly synergistic manner. These results are discussed in relationship to a suggestion that IAA-stimulated H+ secretion and growth involves a rapid effect on CO2 fixation.

Purification and some properties of acetyl-coenzyme A carboxylase from rabbit mammary gland

1. Acetyl-Coa carboxylase from lactating-rabbit mammary gland was purified to homogeneity by the criterion of polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate. 2. Use of phosphate buffer throughout the purification gave low recovery of enzyme. Consequently, Tris buffers were used in the extraction and in selected stages of the purification procedure. 3. The purified enzyme had a specific activity of 5.15 +/- 0.3 μmol of bicarbonate incorporated/min per mg of protein (mean +/- S.E.M. of five preparations). This represents a purification of 257 +/- 16-fold and a yield of 4.3 +/- 0.13%. 4. The kinetic parameters of the purified enzyme were similar to those reported for the enzyme from other tissue sources. 5. The enzyme was assayed by a spectrophotometric assay and by a [14C]bicarbonate-fixation assay. Short incubation were used in the radio-chemical assay to avoid substantial loss of [14C]bicarbonate.

Indoleacetic acid stimulation of phosphorylation and bicarbonate fixation by chloroplast preparations in light

The rate of phosphorylation in illuminated chloroplast preparations from spinach, Swiss chard, or Acetabularia mediterranea was increased by physiological concentrations of indoleacetic acid (IAA), optimum effect being obtained at 10−7 M. Treated chloroplasts gave an increased P/2e ratio, suggesting a greater degree of coupling between electron transport and ATP synthesis. Five minutes after incubation the effect of the hormone was already noticeable. During prolonged illumination the effect of IAA was greatly magnified, raising the phosphorylation rate more than threefold over the control rate. Stimulation of 14C-bicarbonate fixation was also observed in the presence of the same levels of IAA.

Enzymes of the Conversion of Succinate to Glutamate in Extracts of Rumen Microorganisms

Cell-free extracts of mixed rumen microorganisms were incubated in vitro in order to determine the existence and nature of metabolic conversions leading from succinate to glutamate. When succinate was incubated as the substrate in the presence of reduced ferredoxin (FDH), a product was formed, which reacted with 2,4-dinitrophenylhydrazine to give the hydrazone of succinic semialdehyde as determined by paper chromatography. When succinic semialdehyde was incubated in the presence of FDH and 14C-bicarbonate, fixation of label was catalyzed by the extracts. The labelled product was isolated as an organic acid and identified as 2-hydroxyglutaric acid by means of paper chromatography. In the presence of ammonia and NAD, 2-hydroxyglutarate was aminated to a ninhydrin-reactive compound that was identified as glutamate by paper chromatography.From the information obtained, a new pathway for the synthesis of glutamate in rumen microbes was proposed. This pathway entails the reduction of succinate to succinic semialdehyde, followed by reductive carboxylation of succinic semialdehyde to yield 2-hydroxyglutarate, which is then aminated to glutamate. The pathway would agree with the labelling pattern in glutamate produced in the presence of 14C-bicarbonate by mixed rumen microorganisms.