Fructose metabolism in Zymomonas mobilis

Summary In the metabolism of fructose by Zymomonas, the ethanol yield is decreased due to the formation of dihydroxyacetone, mannitol and glycerol. The reduction of fructose to mannitol by an NADPH-dependent mannitol dehydrogenase is apparently coupled to the oxidation of glucose-6-phosphate by glucose-6-phosphate dehydrogenase, which exhibits higher activity with NADP than with NAD as cofactor. The relatively low cell yield on fructose can partly be explained by the loss of ATP in the formation of dihydroxyacetone and glycerol and partly by the toxic effect of dihydroxyacetone and acetaldehyde on the growth of the organism.     

The metabolism of cresols by species of Pseudomonas

1. A comparison of rates of oxidation of various compounds by whole cells indicated that protocatechuate was a reaction intermediate when a non-fluorescent species of Pseudomonas oxidized p-cresol. In contrast, a fluorescent Pseudomonas oxidized 3-methylcatechol and 4-methylcatechol when grown with p-cresol, but did not oxidize protocatechuate. 2. Heat-treated extracts of the fluorescent Pseudomonas oxidized catechol, 3-methylcatechol and 4-methylcatechol to ring-fission products, the spectroscopic properties of which were recorded. Rates of enzymic degradation of these products were also measured. 3. Acetic acid and formic acid were obtained by the action of a Sephadex-treated extract on 3-methylcatechol and 4-methylcatechol respectively. In each case 0.8mol. of the carboxylic acid was formed from 1.0mol. of substrate. 4. Dialysed extracts converted 3-methylcatechol into acetaldehyde and pyruvate, with 4-hydroxy-2-oxovalerate as a reaction intermediate. 4-Methylcatechol was converted first into 4-hydroxy-2-oxohexanoate and then into propionaldehyde and pyruvate. 5. The ring-fission product of catechol was formed from phenol by a fluorescent Pseudomonas, that of 3-methylcatechol was formed from o-cresol and m-cresol, and the ring-fission product of 4-methylcatechol was given from p-cresol. Propionate was readily oxidized by these cells after growth with p-cresol, but this compound was not attacked when phenol, o-cresol or m-cresol served as source of carbon. 6. Cell extracts appeared to attack only one enantiomer of synthetic 4-hydroxy-2-oxohexanoate.     

Fructose 6-phosphate metabolism in plants

The kinetic and regulatory properties of the ATP-dependent phosphofructokinase from various plant tissues are reviewed. Particular attention is given to the differences in properties between the plastid and cytosolic isozymes of this enzyme. A model for fructose 6-phosphate utilization in plants is presented which incorporates a role for the pyrophosphate-dependent phosphofructokinase.     

Adaptive energy metabolism in four chromosomal species of subterranean mole rats

Summary Gross energy intake and apparent dry matter digestibility of animals fed carrots ad lib in the laboratory, were measured in the four chromosomal species of the Spalax ehrenbergi superspecies in Israel. Gross energy intake of 132.8 and 155.9 kJ/day was measured for the 2n=52 and 2n=58 chromosomal mesic species, while in the 2n=54 and 2n=60 chromosomal xeric species it measured only 80.3 and 75.0 kJ/day, respectively. Dry matter digestibility ranged between 92.3 and 95.6% in thefour chromosomal species. The differences in gross energy intake between the mesic and xeric species, appeared to reflect adaptive energy metabolism variation associated with geographic variation in climate, habitat productivity, and food availability.     

中国四种小型鸟类代谢产热的气候适应

采用封闭式流体压力呼吸计 ,分别在 5 - 35°C、 10 - 30°C和 10 - 35°C的环境温度范围内测定了黄眉(Emberizachrysophrys)、红胁绣眼鸟 (Zosteropserythropleura)、画眉 (Garrulaxcanorus)和红嘴相思鸟 (Leio thrixlutea)的耗氧量、热传导、体温等指标 ,探讨了其代谢产热特征。黄眉、红胁绣眼鸟、画眉和红嘴相思鸟的热中性区分别为 2 5 - 30°C、 2 5 - 2 7 5°C、 2 2 5 - 2 7 5°C和 30 - 32 5°C。在 5 - 30°C的温度范围内 ,黄眉和画眉能保持稳定的体温 ,分别为 4 0 5 8± 0 2 6°C和 4 1 6 8± 0 11°C ;红胁绣眼鸟和红嘴相思鸟的体温随环境温度的降低有下降的趋势。在热中性区内 ,黄眉、红胁绣眼鸟、画眉和红嘴相思鸟的平均基础代谢率分别是3 6 5± 0 14、 4 6 9± 0 2 7、 3 5 5± 0 14和 4 2 4± 0 17mlO2 / (g·h) ,分别是体重预期值的 12 8%、 2 30 %、 6 0 %和 12 0 %。在下临界温度以下 ,黄眉、红胁绣眼鸟、画眉和红嘴相思鸟的最小热传导分别是 0 2 4、 0 31、 0 2 1和 0 34mlO2 / (g·h·°C) ,分别是体重预期值的 14 9%、 14 9%、 2 15 %和 2 4 3%。这些小型鸟类的生理生态学特征是 :(1)黄眉和红胁绣眼鸟有高的基础代谢率和相对低的下临界温度 ,适应低温环境     

Enzyme reactions involved in anaerobic cyclohexanol metabolism by a denitrifying Pseudomonas species

The enzymes involved in the anaerobic degration of cyclohexanol were searched for in a denitrifying Pseudomonas species which metabolizes this alicyclic compound to CO₂ anaerobically. All postulated enzyme activities were demonstrated in vitro with sufficient specific activities. Cyclohexanol dehydrogenase catalyzes the oxidation of the substrate to cyclohexanone. Cyclohexanone dehydrogenase oxidizes cyclohexanone to 2-cyclohexenone. 2-Cyclohexenone hydratase and 3-hydroxycyclohexanone dehydrogenase convert 2-cyclohexenone via 3-hydroxycyclohexanone into 1,3-cyclohexanedione. Finally, the dione is cleaved by 1,3-cyclohexanedione hydrolase into 5-oxocaproic acid. Some kinetic and regulatory properties of these enzymes were studied.     

Enzyme reactions involved in anaerobic cyclohexanol metabolism by a denitrifying Pseudomonas species

The enzymes involved in the anaerobic degradation of cyclohexanol were searched for in a denitrifying Pseudomonas species which metabolizes this alicyclic compound to CO2 anaerobically. All postulated enzyme activities were demonstrated in vitro with sufficient specific activities. Cyclohexanol dehydrogenase catalyzes the oxidation of the substrate to cyclohexanone. Cyclohexanone dehydrogenase oxidizes cyclohexanone to 2-cyclohexenone. 2-Cyclohexenone hydratase and 3-hydroxycyclohexanone dehydrogenase convert 2-cyclohexenone via 3-hydroxycyclohexanone into 1,3-cyclohexanedione. Finally, the dione is cleaved by 1,3-cyclohexanedione hydrolase into 5-oxocaproic acid. Some kinetic and regulatory properties of these enzymes were studied.     

Fructose 6-phosphate phosphorylation in Bacteroides species.

6-Phosphofructokinase (6-PFK) activities have been measured in cell extracts from a number of Bacteroides species. Two main types of 6-PFK were found: an ATP-linked 6-PFK and a PPi-linked 6-PFK. In most strains both of these activities were found, although in two strains only ATP-linked 6-PFK was present. The PPi-linked 6-PFK activity was always higher, when both activities were present, and showed Michaelis-Menten kinetics with respect to fructose 6-phosphate. In contrast, the ATP-linked 6-PFK activity usually gave sigmoid kinetics with respect to fructose 6-phosphate, although several strains were found to have activities with Michaelis-Menten kinetics. Conditions for measuring maximum activities of ATP-linked 6-PFK were not identical for different strains, and the activities were rather unstable in extracts. The possible consequences of the observation that most Bacteroides strains possess both an ATP-linked and a PPi-linked 6-PFK are discussed.     

Fructose 2,6-bisphosphate and plant carbohydrate metabolism

The control of the fructose 2,6-bisphosphate (Fru2,6P₂) concentration and its possible role in controlling carbohydrate synthesis and degradation are discussed. This regulator metabolite is involved in the fine tuning of photosynthetic metabolism, and in controlling photosynthetic partitioning, and may also be involved in the response to hormones, wounding, and changing water relations. Study of the mechanisms controlling Fru2,6P₂ concentrations could reveal insights into how these responses are mediated. However, the detailed action of Fru2,6P₂ requires more attention, especially in respiratory metabolism where the background information about the compartmentation of metabolism between the plastid and cytosol is still inadequate, and the potential role of pyrophosphate has to be clarified.     

Fructose 1,6-bisphosphate aldolase activity ofRhizobium species

FDP aldolase was found to be present in the cell-free extracts of Rhizobium leguminosarum, Rhizobium phaseoli, Rhizobium trifolii, Rhizobium meliloti, Rhizobium lupini, Rhizobium japonicum and Rhizobium species from Arachis hypogaea and Sesbania cannabina. The enzyme in 3 representative species has optimal activity at pH 8.4 in 0.2M veronal buffer. The enzyme activity was completely lost by treatment at 60 degrees C for 15 min. The Km values were in the range from 2.38 to 4.55 X 10(-6)M FDP. Metal chelating agents inhibited enzyme activity, but monovalent or bivalent metal ions failed to stimulate the activity. Bivalent metal ions in general were rather inhibitory.     

Oxygen metabolism in Pseudomonas methanica

Three sites of oxygen metabolism in Pseudomonas methanica have been identified on the basis of studies of methane, ethanol and formate oxidation. The three oxidations exhibit different affinities for oxygen and sensitivities to inhibition by cyanide. The results obtained are consistent with the presence of a methane oxygenase and at least two terminal oxidases in Pseudomonas methanica.     

Fructose metabolism via the pentose cycle in tumoral islet cells

In tumoral islet cells (RINm5F line) the phosphorylation of D-fructose is catalyzed by hexokinase rather than fructokinase. Fructose 6-phosphate appears to be preferentially channelled into the pentose cycle, as suggested by a ratio of D-[1-14C]fructose/D-[U-14C]fructose oxidation close to 2.7, the failure to generate 14C-labelled lactate from D-[1-14C]fructose and a poor metabolic response to menadione. When the islet cells are exposed to both D-fructose and D-glucose, however, the metabolism of the former hexose is dramatically modified, fructose 6-phosphate being now formed at a lower rate and preferentially channelled into the glycolytic pathway. These findings illustrate the existence of regulatory steps in fructose catabolism located distally to its site of phosphorylation.