CHARACTERISTICS AND INTERMEDIATES OF SHORT-TERM C-14-O-2 INCORPORATION DURING RIBOSE OXIDATION BY HYDROGENOMONAS FACILIS

CO(2) Fixation, Glutamate Labeling, and the Krebs Cycle in Ribose-grown Hydrogenomonas facilis

Exposure of ribose-grown Hydrogenomonas facilis to (14)CO(2) for 6 to 12 sec during ribose oxidation resulted in labeling of a number of compounds, three of which were glutamate, phosphoglycerate, and pyruvate. Phosphoglycerate and pyruvate were labeled almost exclusively in C(1), suggesting operation of the reductive pentose phosphate cycle. Glutamate was labeled initially to the extent of 90% in C(1) and 10% in C(5), and this was followed by a concentration of radioisotope in C(5). All of the enzymes of the tricarboxylic acid cycle were detectable in ribose-grown cells, and, in general, specific activities were similar to those found in yeast extract-grown cells. Reduced nicotinamide adenine dinucleotide oxidase, aconitase, and the dehydrogenases for pyruvate, alpha-ketoglutarate, and succinate appeared to be of particulate origin. In addition to enzymes of the tricarboxylic acid cycle, an acetyl coenzyme A-stimulated phosphoenolpyruvate carboxylase was found, as was isocitrate lyase. Possible participation of these catalysts in glutamate synthesis is discussed.

Base composition of deoxyribonucleic acid isolated from Athiorhodaceae

Guanine plus cytosine content of deoxyribonucleic acid ranged from 60.5 to 65.0% for five Rhodospirillum species and from 64.4 to 70.3% for six Rhodopseudomonas species. These values were compared to those of two Hyphomicrobiaceae and two hydrogen-oxidizing bacteria.

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.