Metabolic fate of initiation factors after inhibition of protein synthesis in Escherichia coli

Summary The metabolic fate of translation initiation factor after inhibition of protein synthesis by different means has been investigated. We have found a decay in initiation factor activity when protein synthesis is blocked by chloramphenicol but not during arginine starvation of PA1 (Rel^–) or PA2 (Rel⁺) strains or during puromycin incubation. These results suggest that inactivation of certain initiation factors occurs when the regeneration of ribosomal subunits from polysomes is inhibited in the cells.Complementation experiments indicate that IF₃ factor activity is preferentially affected during chloramphenicol treatment.Same preferential inhibition of IF₃ activity seems to occur during in vitro incubation of crude IF. 70S ribosomes or 30S subunits protect this factor against the inactivation. Preliminary results seem tosuggest that ATP is implicated in this in vitro inactivation process.     

La theorie du controle du metabolisme controle et regulation

Resume La théorie du Contróle du Métabolisme (Kacser & Bums, 1973; Heinrich & Rapoport, 1974) décrit comment un réseau métabolique répond à de petites perturbations au voisinage d'un état stationnaire. Deux types de coefficients sont définis: les coefficients d'élaslicité qui quantifient les variations des vitesses des étapes isolées et les coefficients de contrôle qui expriment la réponse globale du réseau aux perturbations d'une étape donnée. Des relations entre ces coefficients existent (Relations de sommation et relations de connexion) (pour une revue, voir Mazat et Jean-Bart (1988)).On ne fait pas toujours la distinction entre Contrôle et Régulation. En fait, il apparait que la notion de régulation, si elle est trés claire lorsqu'il s'agit de la régulation de l'activité d'un enzyme, West plus du tout définie lorsqu'il s'agit d'un réseau métabolique dans son ensemble.Le but de l'exposé est de proposer une définition de la régulation d'un réseau métabolique et de montrer quelles relations peuvent exister entre lee phénomènes de régulation et la théorie du contrôle du métabolisme.Quelques exemples seront donnés pour illustration.     

miR‐124‐dependent tagging of synapses by synaptopodin enables input‐specific homeostatic plasticity

Homeostatic synaptic plasticity is a process by which neurons adjust their synaptic strength to compensate for perturbations in neuronal activity. Whether the highly diverse synapses on a neuron respond uniformly to the same perturbation remains unclear. Moreover, the molecular determinants that underlie synapse‐specific homeostatic synaptic plasticity are unknown. Here, we report a synaptic tagging mechanism in which the ability of individual synapses to increase their strength in response to activity deprivation depends on the local expression of the spine‐apparatus protein synaptopodin under the regulation of miR‐124. Using genetic manipulations to alter synaptopodin expression or regulation by miR‐124, we show that synaptopodin behaves as a “postsynaptic tag” whose translation is derepressed in a subpopulation of synapses and allows for nonuniform homeostatic strengthening and synaptic AMPA receptor stabilization. By genetically silencing individual connections in pairs of neurons, we demonstrate that this process operates in an input‐specific manner. Overall, our study shifts the current view that homeostatic synaptic plasticity affects all synapses uniformly to a more complex paradigm where the ability of individual synapses to undergo homeostatic changes depends on their own functional and biochemical state.     

An analysis of the volatile flavour compounds in a soft raw goat milk cheese

The major components of the musty cow rind cheeses were identified in a soft raw goat milk cheese as heptan-2-one, nonan-2-one, their corresponding secondary alcohols, some esters and sulfur compounds. Their production was associated with the manufacturing process and its influence on the microbial activity. However a specificity in goat cheese compounds was displayed concerning in particular limonene and some ketones, alcohols and aldehydes.     

Grazing of echinoderm larvae (Paracentrotus lividus and Arbacia lixula) on naturally occurring particulate matter

Larvae (72 hr old) of P. lividus and A. lixula grazed on varioussuspensions of natural particulate matter with a size rangeof 2 to 30 microns, and on two species of algae (Phaeodactylumtricor-nutum and Nitzschia sp.) — Larvae graze most in the size range where the particleconcentration is highest. — If larvae deplete certain size categories of particlesthey then graze other size ranges in which the concentrationis still high. — The grazing rate of the two species varied between 988and 91.949 µm³ per pluteus per hour. — For A. lixula larvae the grazing rate increases withincreasing temperature to a maximum at 22°C.     

Evaluation of the bioremoval of Cr(VI) and TOC in biofilters under continuous operation using response surface methodology

In the present study, the bioremoval of Cr(VI) and the removal of total organic carbon (TOC) were achieved with a system composed by an anaerobic filter and a submerged biofilter with intermittent aeration using a mixed culture of microorganisms originating from contaminated sludge. In the aforementioned biofilters, the concentrations of chromium, carbon, and nitrogen were optimized according to response surface methodology. The initial concentration of Cr(VI) was 137.35 mg l⁻¹, and a bioremoval of 85.23% was attained. The optimal conditions for the removal of TOC were 4 to 8 g l⁻¹ of sodium acetate, >0.8 g l⁻¹ of ammonium chloride and 60 to 100 mg l⁻¹ of Cr(VI). The results revealed that ammonium chloride had the strongest effect on the TOC removal, and 120 mg l⁻¹ of Cr(VI) could be removed after 156 h of operation. Moreover, 100% of the Cr(VI) and the total chromium content of the aerobic reactor output were removed, and TOC removals of 80 and 87% were attained after operating the anaerobic and aerobic reactors for 130 and 142 h, respectively. The concentrations of cells in both reactors remained nearly constant over time. The residence time distribution was obtained to evaluate the flow through the bioreactors.