Ribulose diphosphate carboxylase and CO2 incorporation in extracts of Hydrogenomonas facilis

Molecular and cellular regulation of autotrophic carbon dioxide fixation in microorganisms

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Factors affecting the synthesis and degradation of ribulose-1,5-diphosphate carboxylase in Hydrogenomonas facilis and Hydrogenomonas eutropha

Hydrogenomonas facilis and H. eutropha cultured in fructose medium retained high levels of ribulose-1,5-diphosphate carboxylase only when the following conditions were fulfilled: low aeration, FeCl(3) addition to fructose medium, and cell harvest at or prior to mid-exponential phase of growth. Repression of carboxylase synthesis was demonstrated under conditions of high oxygen tension during growth of H. eutropha on fructose. Upon depletion of fructose in the growth medium, carboxylase activity fell abruptly in both organisms. The decline could not be attributed to a repressive mechanism. Rapid inactivation of carboxylase was promoted by transfer of mid-exponential-phase H. eutropha to a basal salts medium lacking fructose. During severe fructose starvation, N(2), H(2), 80% H(2) to 20% air, 2,4-dinitrophenol, actinomycin D, streptomycin, bicarbonate, and magnesium ion deficiency spared carboxylase. Nitrogen starvation or chloramphenicol afforded no protection during severe starvation. In vitro inactivation was also demonstrated in crude cell-free extracts from nonstarved, fructose-grown H. eutropha. Substrate bicarbonate protected against this loss. Inactivation of the carboxylase could not be demonstrated either by starvation of autotrophically grown cells or in autotrophic extracts. Autotrophic extracts mixed with heterotrophic extracts lost their carboxylase activity, but mixing with heterotrophic extracts that had been heated to 50 C resulted in no loss of activity. Mechanisms are proposed to accommodate these observations.

Regulation of autotrophic and heterotrophic carbon dioxide fixation in Hydrogenomonas facilis

After growth on various carbon sources, sonic extracts of Hydrogenomonas facilis contained ribulosediphosphate (RuDP) carboxylase and phosphoribulokinase (Ru5-P kinase). After very short sonic treatment, a reductive adenosine triphosphate (ATP)-dependent incorporation of (14)CO(2) was also detectable. Reduced nicotinamide adenine dinucleotide (NADH(2)) served as reductant 30-fold more effectively than reduced nicotinamide adenine dinucleotide phosphate (NADPH(2)). Adenosine 5'-phosphate (AMP) and adenosine 5'-pyrophosphate (ADP) inhibited Ru5-P kinase and NADH(2)-, ATP-dependent CO(2) fixation. The levels and duration of CO(2) fixation suggested that it is a cyclic process. The requirement of reduced pyridine nucleotide and ATP and the sensitivity of fixation to AMP and ADP support the conjecture that it occurs via the Calvin cycle. After thorough study of variables affecting catalysis, specific activities (millimicromoles of substrate disappearing per milligram of protein) at 30 C were determined for RuDP carboxylase (C), Ru5-P kinase (K) and ATP-, NADH(2)- dependent CO(2) fixation (CO(2) F) after growth autotrophically on fructose, glucose, ribose, glutamate, lactate, succinate, and acetate. Values for these growth modes were, respectively-for C: 67.3, 51.1, 51.4, 24.6, 2.05, 10.2, 2.25, 1.4; for K: 24.7, 24.0, 23.2, 14.2, 12.8, 12.9, 13.4, 2.8; and for CO(2) F: 4.54, 4.83, 3.10, 2.87, 0.85, 1.51, 0.24, 0.41. The qualitative parallel between values for RuDP carboxylase and CO(2) fixation suggests that one major control point in fixation is the step catalyzed by RuDP carboxylase.

Generation of reducing power in chemosynthesis. 3. Energy-linked reduction of pyridine nucleotides in Thiobacillus novellus

Aleem, M. I. H. (Research Institute for Advanced Studies, Baltimore, Md.). Generation of reducing power in chemosynthesis. III. Energy-linked reduction of pyridine nucleotides in Thiobacillus novellus. J. Bacteriol. 91:729-736. 1966.-Cell-free extracts from Thiobacillus novellus. catalyzed an adenosine triphosphate (ATP)-dependent reduction of pyridine nucleotides anaerobically, or aerobically when the respiratory chain was inhibited by azide. The exogenous electron donor employed for the reduction of nicotinamide adenine dinucleotide or nicotinamide adenine dinucleotide phosphate (NADP) was thiosulfate, formate, or mammalian ferrocytochrome c. In the latter case, the oxidation of ferrocytochrome c was observed with the concomitant reduction of the pyridine nucleotide. Values calculated for the molar ratios of ATP utilized-NADP reduced and of cytochrome c oxidized-NADP reduced were 1:1 and 2:1, respectively. The energy-dependent reduction of the pyridine nucleotides was inhibited by Atabrine or amytal and by low concentrations of the uncouplers of oxidative phosphorylation such as 2,4-dinitrophenol and carbonyl cyanide m-chlorophenyl hydrazone. Evidence is presented showing that the reduced pyridine nucleotides are essential for providing the reducing power for the energy-dependent reduction of carbon dioxide in T. novellus.