Translocation and proteolytic processing of nascent secretory polypeptide chains: two functions associated with the ribosomal domain of the endoplasmic reticulum.

Rat liver microsomes were subfractionated by isopycnic centrifugation in sucrose gradient. The subfractions were assayed for translocation and proteolytic processing of nascent polypeptides in a rabbit reticulocyte lysate programmed with total RNA from human term placenta. The distribution of the translocation and processing of prelactogen through the gradient correlated with that of the microsomal RNA (ribosomes). Microsomes became inactive upon incubation with elastase, but the proteolyzed membranes recovered their activity by recombination with the soluble and active fragment of the docking protein (SRP-receptor) from dog pancreas. When this fragment was combined with the gradient subfractions, or with the subfractions inactivated by incubation with elastase, the density profile of the translocation activity remained similar to that of RNA. Thus, its distribution cannot be accounted for merely by that of the docking protein; another membrane constituent, still unidentified, is both necessary for translocation of polypeptides and restricted to the rough portions of the endosplamic reticulum. Signal peptidase was assayed in the absence of protein synthesis, by use of preformed prelactogen and detergent-disrupted microsomes. Its density distribution was also similar to that of RNA. Several components of the endosplamic reticulum now appear to be segregated within restricted areas on either side of the membrane, and to make up a biochemically distinct domain. We propose to call it the ribosomal domain in consideration of its contribution to protein biosynthesis by bound ribosomes. This domain probably accounts for a greater part of the membrane area at the cytoplasmic than at the luminal surface, as postulated earlier to explain how enzymes of the cytoplasmic surface are relatively less abundant in the rough microsomes than those of the luminal surface [Amar-Costesec A. & Beaufay H. (1981) J. Theor. Biol. 89, 217-230]

Valorisation of partially oxidized tailings in a cover system to reclaim an old acid generating mine site

The reclamation of acid-generating mine tailings typically involves building cover systems to limit interactions with water or oxygen. The choice of cover materials is critical to ensure long-term performance, and partly determines the environmental footprint of the reclamation strategy. The objective of this research was to evaluate if tailings pre-oxidized on-site could be used in cover systems. Column experiments were performed to assess the effectiveness of a cover with capillary barrier effects (CCBE), where the moisture retention layer (MRL) was made of pre-oxidized tailings with little to no remaining sulfides (LS tailings). The columns were submitted to regular wetting and drying cycles, and their hydrological and geochemical behaviour was monitored for 510 days. The LS tailings showed satisfying hydrological properties as an MRL and remained saturated throughout the test. The concentrations of Cu in the drainage decreased by more than two orders of magnitude compared to non-covered tailings. In addition, the pH increased by nearly one unit compared to the control column, and Fe and S concentrations decreased by around 50%. Despite these improvements, the leachate water remained acidic and contaminated, indicating that acid drainage continued to be generated despite a hydrologically efficient CCBE