Limited proteolysis ofSaccharomyces cerevisiae phosphoenolpyruvate carboxykinase

Incubation ofSaccharomyces cerevisiae phosphoenolpyruvate carboxykinase with trypsin under native conditions cases a time-dependent loss of activity and the production of protein fragments. Cleavage sites determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and sequence analyses identified protease-sensitive peptide bonds between amino acid residues at positions 9–10 and 76–77. Additional fragmentation sites were also detected in a region approximately 70–80 amino acids before the carboxyl end of the protein. These results suggest that the enzyme is formed by a central compact domain comprising more than two thirds of the whole protein structure. From proteolysis experiments carried out in the presence of substrates, it could be inferred that CO₂ binding specifically protects position 76–77 from trypsin action. Intrinsic fluorescence measurements demonstrated that CO₂ binding induces a protein conformational change, and a dissociation constant for the enzyme CO₂ complex of 8.2±0.6 mM was determined     

Electron microscopic and biochemical study of lipoprotein synthesis in the isolated perfused rat liver

The isolated perfused rat liver was used to study the 300-800 A electron-opaque bodies which had previously been described in the liver cell Golgi apparatus, smooth endoplasmic reticulum, and space of Disse. When the perfusion medium was enriched with linoleate, the number and electron opacity of these particles increased markedly. Sequential biopsies showed that they appeared first in the smooth surfaced terminal ends of the rough reticulum, the smooth endoplasmic reticulum proper, and the Golgi apparatus and later in the space of Disse. After 60 min of perfusion, particles of the same size and shape as those in the liver cells could be isolated in large numbers from the d < 1.006 fraction of the perfusate. Control livers perfused with an identical medium but without linoleate did not show these changes. Puromycin markedly depressed the production of 300-800 A particles by livers perfused with an oleate-rich medium; however, it did not interfere with the formation of large cytoplasmic droplets of neutral fat. In keeping with these findings, puromycin blocked the incorporation of oleate-(14)C into lipoprotein triglyceride isolated from the perfusate, but did not interfere with the appearance of the labeled fatty acid in tissue triglyceride. Puromycin also blocked the incorporation of leucine-(3)H into both tissue protein and perfusate lipoprotein. We concluded that the 300-800 A particles observed are, in all likelihood, very low density lipoproteins and that their formation is blocked by puromycin, presumably through interference with the synthesis of their apoprotein.     

Effects of periodic flooding on the water chemistry and primary production of the Mapire systems (Venezuela)

The Mapire river mouth forms a complex floodplain system, where the river behaves as a river during the dry season, but changes to a transient lake which partially covers the inundation forest during the rainy season. Thus, we expected changes in water chemistry and a gradual increase of primary production during high waters. The system was sampled monthly for one year; two floodplain lakes were also studied for comparative purposes. Variations in the concentration of macro- and micronutrients occurred in a pulse-like manner and seemed to relate to mechanisms at work in the transient lake. Dissolved oxygen showed a stratification with low values at the bottom, but never reached anoxia. Net and gross primary production and respiration did not show any clear spatial pattern, reflecting a mosaic of different biochemical states within the transient lake. Heterotrophy tended to prevail in the transient lake, while autotrophy dominated floodplain lakes.     

Transcriptomics of the grape berry shrivel ripening disorder

Plant Molecular Biology - The lower expression at veraison of several ripening master regulators “switch genes” can play a central role in the induction of the berry shrivel ripening...     

Triple benefits from spatial resource management

Standard fishery management models suggest that regulations designed to produce maximum rent should reduce effort – and thus employment – from its open-access level. Using a simple diffusion model, we show that the opposite can be true when the spatial distribution of effort, as well as the total amount of effort, can be controlled. Under certain ecological and economic circumstances that we describe, optimal spatial management can produce “triple benefits” compared to open access: an increase in rent, an increase in standing stock, and an increase in employment. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The effect of social learning in a small population facing environmental change: an agent-based simulation

Learning is defined as behavioral modification due to experience, social or asocial. Social learning might be less costly than asocial learning and allow the rapid accumulation of learned traits across generations. However, the benefits of social learning in a small population of individuals relying on local interactions and experiencing environmental change are not well understood yet. In this study, we used agent-based simulations to address this issue by comparing the performance of social learning to asocial learning and innate behavior, in both a static and a changing environment. Learning was modeled using neural networks, and innate behavior was modeled using genetically coded behaviors. The performance of 10 mobile simulated agents was measured under three environmental scenarios: static, abrupt change and gradual change. We found that social learning allows for a better performance (in terms of survival) than asocial learning in static and abrupt-change scenarios. In contrast, when changes are gradual, social learning delays achieving the correct alternative, while asocial learning facilitates innovation; interestingly, a mixed population (social and asocial learners) performs the best.