Metabolic Machinery (metabolic + machinery)

Distribution by Scientific Domains

Selected Abstracts

Abundances of crenarchaeal amoA genes and transcripts in the Pacific Ocean

Matthew J. Church
Summary Planktonic Crenarchaea are thought to play a key role in chemolithotrophic ammonia oxidation, a critical step of the marine nitrogen (N) cycle. In this study, we examined the spatial distributions of ammonia-oxidizing Crenarchaea across a large (,5200 km) region of the central Pacific Ocean. Examination of crenarchaeal 16S rRNA, ammonia monooxygenase subunit A (amoA) genes, and amoA transcript abundances provided insight into their spatial distributions and activities. Crenarchaeal gene abundances increased three to four orders of magnitude with depth between the upper ocean waters and dimly lit waters of the mesopelagic zone. The resulting median value of the crenarchaeal amoA: 16S rRNA gene ratio was 1.3, suggesting the majority of Crenarchaea in the epi- and mesopelagic regions of the Pacific Ocean have the metabolic machinery for ammonia oxidation. Crenarchaeal amoA transcript abundances typically increased one to two orders of magnitude in the transitional zone separating the epipelagic waters from the mesopelagic (100,200 m), before decreasing into the interior of the mesopelagic zone. The resulting gene copy normalized transcript abundances revealed elevated amoA expression in the upper ocean waters (0,100 m) where crenarchaeal abundances were low, with transcripts decreasing into the mesopelagic zone as crenarchaeal gene abundances increased. These results suggest ammonia-oxidizing Crenarchaea are active contributors to the N cycle throughout the epi- and mesopelagic waters of the Pacific Ocean. [source]

Avian seasonal metabolic variation in a subtropical desert: basal metabolic rates are lower in winter than in summer

Ben Smit
Summary 1Most small birds inhabiting temperate latitudes in the Holarctic increase basal metabolic rate (BMR) in winter, a pattern thought to reflect the up-regulation of metabolic machinery required for enhanced winter cold tolerance. In contrast, patterns of seasonal BMR variation in birds inhabiting subtropical latitudes are largely unknown. In this study, we investigate seasonal BMR changes in species from subtropical latitudes, and analyse global variation in the direction and magnitude of these responses. 2We estimated winter and summer BMR in five species resident in the Kalahari Desert, using flow-through respirometry to measure O2 consumption and CO2 production in birds held overnight in a field laboratory. 3In all five species, mass-specific BMR was significantly lower in winter than in summer, with mean reductions of 23% in African scops-owls (Otus senegalensis), 30% in pearl-spotted owlets (Glaucidium perlatum), 35% in fork-tailed drongos (Dicrurus adsimilis), 29% in crimson-breasted shrikes (Laniarius atrococcinneus), and 17% in white-browed sparrow-weavers (Plocepasser mahali). 4An analysis of global variation in seasonal BMR changes reveals that their magnitude and direction vary with latitude, ranging from pronounced winter increases at high latitudes where winters are extremely cold, to the opposite pattern in warmer, subtropical environments. 5Our empirical results for five species, taken together with the analysis of global variation, are consistent with the hypothesis that winter metabolism in subtropical environments is driven primarily by the need for energy and/or water conservation rather than cold tolerance. [source]

Improving cellular function through modulation of energy metabolism

D. Maes
The ambivalent consequences of mitochondrial stimulation on cellular activity have been well established. Mitochondria supply the cell with energy through a process of oxidative phosphorylation but thereby generate free radicals, resulting in the accumulation of hydrogen peroxide in the cytoplasm. We have investigated the impact of cellular senescence as well as UV irradiation, on the balance between these two activities. The adenosine triphosphate (ATP) level, DNA and protein synthesis in fibroblasts obtained from donors between 30 and 90 years of age appeared to be significantly influenced by the aging process. Both DNA and protein synthesis could be stimulated by increasing intracellular ATP levels. In-vitro senescent fibroblasts showed a reduction in the level of ATP as well as a shift in mitochondrial membrane potential. At the same time, there was an increase in intracellular hydrogen peroxide with increasing population doubling, indicating a clear dysfunction of the metabolic machinery in the mitochondria of senescent cells. To counteract this degradation of the energy pool, we treated cells with creatine, which is known to restore the pool of phosphocreatine in the mitochondria. Creatine treatment significantly increased cell survival after UV exposure, stimulated the repair of UVB-induced DNA damage in keratinocytes and caused a significant reduction in the number of sunburn cells in a UVB-exposed reconstituted skin model. These results clearly indicate that restoration of the energy pool in mitochondria increased cellular self-defense mechanism. These data show the important role played by the mitochondrial energy metabolism on the aging process, and indicate a possible therapy that can be used to counteract this negative effect. Treatment with creatine seems to provide the necessary boost to the cellular metabolism, which leads to an induction of a significant amount of protection and repair to human skin cells. [source]

Cultured Granule Cells and Astrocytes from Cerebellum Differ in Metabolizing Sphingosine

Laura Riboni
Sphingosine metabolism was studied in primary cultures of differentiated cerebellar granule cells and astrocytes. After a 2-h pulse with [C3 - 3H]sphingosine at different doses (0.1-200 nmol/mg of cell protein), both cell types efficiently incorporated the long chain base ; the percentage of cellular [3H]sphingosine over total label incorporation was extremely low at sphingosine doses of <10 nmol/mg of cell protein and increased at higher doses. Most of the [3H]sphingosine taken up underwent metabolic processing by N -acylation, 1-phosphorylation, and degradation (assessed as 3H2O released in the medium). The metabolic processing of exogenous sphingosine was extremely efficient in both cells, granule cells and astrocytes being able to metabolize, respectively, an amount of sphingosine up to 80- and 300-fold the cellular content of this long chain base in 2 h. At the different doses, the prevailing metabolic route of sphingosine was different. At lower doses and in a wide dose range, the major metabolic fate of sphingosine was N -acylation. With increasing doses, there was first increased sphingosine degradation and then increased levels of sphingosine-1-phosphate. The data demonstrate that, in neurons and astrocytes, the metabolic machinery devoted to sphingosine processing is different, astrocytes possessing an overall higher capacity to synthesize the bioactive compounds ceramide and sphingosine-1-phosphate. [source]

Autoinduction and signal transduction in the regulation of staphylococcal virulence

Richard P. Novick
Summary The accessory genes of Staphylococcus aureus, in-cluding those involved in pathogenesis, are controlled by a complex regulatory network that includes at least four two-component systems, one of which, agr, is a quorum sensor, an alternative sigma factor and a large set of transcription factors, including at least two of the superantigen genes, tst and seb. These regulatory genes are hypothesized to act in a time- and population density-dependent manner to integrate signals received from the external environment with the internal metabolic machinery of the cell, in order to achieve the production of particular subsets of accessory/virulence factors at the time and in quantities that are appropriate to the needs of the organism at any given location. From the standpoint of pathogenesis, the regulatory agenda is presumably tuned to particular sites in the host organism. To address this hypothesis, it will be necessary to understand in considerable detail the regulatory interactions among the organism's numerous controlling systems. This review is an attempt to integrate a large body of data into the beginnings of a model that will hopefully help to guide research towards a full-scale test. [source]

Changes in zinc uptake in response to ascorbic acid and folic acid in rat liver slices under normal and oxidative stress conditions

BIOFACTORS, Issue 1 2007
R.S. Tupe
Abstract Zinc plays a dual role, as an integral part of metabolic machinery and in defense against reactive oxygen species. Hepatocytes are important sites for zinc metabolism for synthesis of zinc metalloproteins and maintaining its homeostasis. However, the factors influencing post absorptive zinc metabolism under normal and oxidative stress (OS) conditions are not well understood. Using rat liver slices, we conducted a series of four in vitro zinc uptake experiments to study influence of ascorbic acid and folic acid in normal and oxidative stress conditions with Zn concentrations representing deficient to excess states (7.7,30.7 millimole/L). Zinc uptakes under OS at these four zinc levels were lower than the normal conditions. Folic acid showed significant inhibitory effect on zinc uptake under both normal and OS conditions in a dose response manner. Nevertheless, dose response of ascorbic acid at four zinc levels indicated its marked enhancing effect under OS condition. Differences in zinc uptake trend lines between the normal and OS conditions for interaction of both the vitamins narrowed down as the zinc levels increased. Our results suggest that folic acid causes inhibitory effect, while ascorbic acid may be protective in OS with reference to zinc uptake. [source]