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At least 19 recordsLinked to original sources
PubMed1976

Bacterial yields on methanol, methylamine, formaldehyde, and formate.

Several bacteria utilizing C1-compounds as sole carbon sources were grown on these substrates in continuous culture. The molar yield values (g of cell dry wt/mol of substrate utilized) of bacteria which utilize C1-compounds via the ribulose monophosphate pathway were between 15.7 to 17.3 when grown on methanol; while the molar yield values of bacteria which use the serine pathway for the assimilation of C1-compounds varied between 9.8 and 13.1. The molar yield values of different bacteria which use the serine pathway decreased as the oxidation levels of the C1-growth substrates increased. On formaldehyde the values were between 7.2 to 9.6, whereas on formate the values varied from 3.3 to 6.9. It appears that bacteria utilize C1-compounds more efficiently via the ribulose monophosphate pathway than via the serine pathway. The oxidation step from methanol to formaldehyde (and from methylamine to formaldehyde) in the bacteria studied may be energy yielding. A comparison has been made between the experimental yield values obtained and theoretical values.

Formaldehyde↗
PubMed1978

Maintenance requirements for bacteria growing on C1-compounds.

The maintenance coefficient, ms (mmol substrate/g cell dry wt hr), of two distinct groups of C1-utilizing bacteria has been determined by growing the organisms in an aerobic continuous culture limited by different C1 growth substrates. For growth on methanol, ms = 2.5 +/- 0.3 for Pseudomonas C; 3.9 +/- 0.7 for Ps. methylotropha (these bacteria utilize methanol via the ribulose monophosphate pathway of formaldehyde fixation); 1.5 +/- 0.2 for Pseudomonas 1, and 2.3 +/- 0.4 for Pseudomonas 135 (the latter bacteria utilize C1-compounds via the serine pathway). For growth on formaldehyde, ms = 1.5 +/- 0.3 for Pseudomonas 1 and 2.7 +/- 0.7 for Pseudomonas 135, whereas on formate the values for ms are 1.0 +/- 0.2 and 4.4 +/- 1.3; respectively. Although the maintenance coefficients did not differ systematically between the two groups of bacteria, the maintenance requirements per generation of the serine pathway bacteria were considerably higher (8.7 vs. 3.9) owing to their slower growth rate. The maximum molar yield values, YMmax (g cell dry wt/mol substrate utilized), corrected for the maintenance energy of bacteria which utilize C1-compounds via the ribulose monophosphate pathway averaged 19.1 when grown on methanol, while the values for bacteria which use the serine pathway averaged 13.5. On formaldehyde an average value of 11.5 is obtained and on formate the average value was 7.4 in the serine pathway bacteria.

Adenosine Triphosphate↗
PubMed1978

Regulation of photosynthetic carbon assimilation.

It may be concluded that the conversion of PGA to DPGA plays a key role in induction and in the regulation of cycle activity. The high concentrations of PGA in actively photosynthesizing chloroplasts reflect this role and the control exerted by adenylate ratios. Thus the cycle can operate at its maximum rate only in the presence of high PGA and low ribulose 5-phosphate concentrations. Once induction is complete, the reductive pentose phosphate pathway will continue to function at its maximum rate if sink activity within the cytoplasm makes available sufficient Pi to support rapid export of triose phosphate. If triose phosphate tends to build up in the straoma, it will favor pentose monophosphate accumulation. A relative excess of ribulose 5-phosphate would, in turn, inhibit PGA reduction (and hence its own formation) by drawing too heavily on the available ATP.

Adenosine Diphosphate↗
PubMed1990

D-ribulokinase from Klebsiella pneumoniae for continuous production of D-(-)-ribulose-5-phosphate.

The production of D-ribulose-5-phosphate in an enzyme membrane reactor was examined. Phosphoryl transfer from ATP to D-ribulose was catalysed by D-ribulokinase isolated from Klebsiella pneumoniae. For production of D-ribulose-5-phosphate the phosphoryl donor ATP was used either in stoichiometric or in catalytic amounts. Using catalytic amounts of ATP requires a second enzyme, e.g. pyruvate kinase, to regenerate ATP. The kinetic parameters for D-ribulokinase and pyruvate kinase were determined to calculate the performance of an enzyme membrane reactor for continuous production of D-ribulose-5-phosphate. Both processes operated for more than 200 h. Regardless of whether ATP was used in catalytic or stoichiometric amounts, about the same production parameters were determined. In continuous production space/time yields of 117 g (with ATP regeneration) and 103 g (without ATP regeneration) of D-ribulose-5-phosphate l -1 per day were reached.

Adenosine Triphosphate↗
PubMed1978

Glucose-6-phosphate dehydrogenase of Anabaena sp. Kinetic and molecular properties.

The kinetic and molecular properties of cyanobacterial glucose-6-phosphate dehydrogenase, partly purified from Anabaena sp. ATCC 27893, show that it undergoes relatively slow, reversible transitions between different aggregation states which differ in catalytic activity. Sucrose gradient centrifugation and polyacrylamide gel electrophoresis reveal three pincipal forms, with approximate molecular weights of 120 000 (M1), 240 000 (M2) and 345 000 (M3). The relative catalytic activities are: M1 less than M2 less than M3. In concentrated solutions of the enzyme, the equilibrium favors the more active, oligomeric forms. Dilution in the absence of effectors shifts the equilibrium in favor of the M1 form, with a marked diminution of catalytic activity. This transition is prevented by a substrate, glucose-6-phosphate, and also by glutamine. The other substrate, nicotinamide adenine dinucleotide phosphate (NADP+), and (in crude cell-free extracts) ribulose-1,5-diphosphate are negative effectors, which tend to maintain the enzyme in the M1 form. The equilibrium state between different forms of the enzyme is also strongly dependent on hydrogen ion concentration. Although the optimal pH for catalytic activity is 7.4, dissociation to the hypoactive M1 form is favored at pH values above 7; a pH of 6.5 is optimal for maintenance of the enzyme in the active state. Reduced nicotamide adenine dinucleotide phosphate (NADPH) and adenosine 5'-triphosphate (ATP), inhibit catalytic activity, but do not significantly affect the equilibrium state. The relevance of these findings to the regulation of enzyme activity in vivo is discussed.

Adenosine Triphosphate↗
PubMed1978

Electron microscopy of methanol-utilizing bacteria.

Two different groups of methanol-utilizing bacteria were studied by electron microsocpy. Bacteria using the serine pathway for the assimilation of methanol were found to have a thin cell envelope (outer membrane, periplasmic area and cytoplasmic membrane). Those using the assimilatory ribulose monophosphate pathway of formaldehyde fixation had a much thicker cell envelope and in the case of Pseudomonas C protrusions of the outer membrane were found.

Cell Membrane↗
PubMed1990

Affinity labeling of spinach phosphoribulokinase subsequent to S-methylation at Cys16.

The chloroplast enzyme phosphoribulokinase is reversibly deactivated by oxidation of Cys16 and Cys55 to a disulfide. Although not required for catalysis, Cys16 is an active-site residue positioned at the nucleotide-binding domain (Porter and Hartman, 1988). The hyperreactivity of Cys16 has heretofore limited further active-site characterization by chemical modification. To overcome this limitation, the partially active enzyme, S-methylated at Cys16, has been probed with a potential affinity reagent. Treatment of methylated enzyme with bromoacetylethanolamine phosphate results in essentially complete loss of catalytic activity. Inactivation follows pseudo-first-order kinetics and exhibits a rate saturation with an apparent Kd of 3-4 mM. ATP, but not ribulose 5-phosphate, affords substantial protection. Complete inactivation correlates with incorporation of 1 mol of [14C]reagent per mole of enzyme subunit. Amino acid analysis of the [14C]-labeled enzyme demonstrates that only cysteine is modified, and mapping of tryptic digests shows that Cys55 is a major site of alkylation. These results indicate that Cys55 is also located in the ATP-binding domain of the active-site.

Adenosine Triphosphate↗
PubMed1986

The measurement of xylulose 5-phosphate, ribulose 5-phosphate, and combined sedoheptulose 7-phosphate and ribose 5-phosphate in liver tissue.

A modification of the method of Kauffman et al. (F. C. Kauffman, J. G. Brown, J. V. Passonneau, and O. H. Lowry (1969) J. Biol. Chem. 244, 3647-3653) for the spectrophotometric determination of xylulose 5-phosphate, ribulose 5-phosphate, and combined ribose 5-phosphate and sedoheptulose 7-phosphate in tissue extract is presented. Using commercially available enzymes all three assays come to a clear endpoint with the assays described. Values for these metabolites in liver in three dietary states are reported; 48 h starved, ad libitum feeding of standard NIH rat ration, and meal feeding of a fat-free diet. Xylulose 5-phosphate values were 3.8 +/- 0.3, 8.6 +/- 0.3, and 66.3 +/- 8.3 nmol/g. Ribulose 5-phosphate values were 3.4 +/- 0.3, 5.8 +/- 0.2, and 37.1 +/- 5.3 nmol/g. Combined ribose 5-phosphate and sedoheptulose 7-phosphate were 29.3 +/- 0.3, 38.2 +/- 1.2, and 108.2 +/- 14.5 nmol/g. The ratio of measured tissue content of [xylulose 5-phosphate]/[ribulose 5-phosphate] was found to be 1.12 +/- 0.07 in starved animals, 1.48 +/- 0.04 in ad libitum fed animals and 1.78 +/- 0.03 in low-fat meal fed animals. These data are in good agreement with the range of equilibrium constants reported for this reaction, suggesting that the ribulose 5-phosphate 3-epimerase reaction (EC 5.1.3.1) is a near equilibrium reaction despite a more than 10-fold change in the tissue content of these metabolites.

Animals↗