PubMed Health⌕ Search

Biomedical subjects

C de Duve

Publications and source records attributed to C de Duve.

At least 19 recordsLinked to original sources
PubMed1987

Biogenesis of the glycosome in Trypanosoma brucei: the synthesis, translocation and turnover of glycosomal polypeptides.

Glycosomes, the microbodies of Trypanosoma brucei, contain a number of enzymes involved in glucose and glycerol metabolism. The biogenesis of three of these enzymes has been studied. Aldolase, D-glyceraldehyde-3-phosphate dehydrogenase and NAD-linked glycerol-3-phosphate dehydrogenase are all synthesized in the cytosol on free rather than on membrane-bound polysomes. In vitro, as well as in vivo, these polypeptides are synthesized at their mature size, and no evidence was found for any processing upon entry into the glycosomes. Continuous and pulse-chase labelling experiments with procyclic trypomastigotes revealed that the enzymes have a half-life in the cytosol of approximately 3 min or less, and then turn over rapidly in the glycosomes, with half-lives as short as 30 min.

Animals↗
PubMed1987

Selection by differential molecular survival: a possible mechanism of early chemical evolution.

A model is proposed to account for selective chemical evolution, progressing from a relatively simple initial set of abiotic synthetic phenomena up to the elaborately sophisticated processes that are almost certainly required to produce the complex molecules, such as replicatable RNA-like oligonucleotides, needed for a Darwinian form of selection to start operating. The model makes the following assumptions: (i) that a small number of micromolecular substances were present at high concentration; (ii) that a random assembly mechanism combined these molecules into a variety of multimeric compounds comprising a wide repertoire of rudimentary catalytic activities; and (iii) that a lytic system capable of breaking down the assembled products existed. The model assumes further that catalysts supplied with substrates were significantly protected against breakdown. It is shown that, by granting these assumptions, an increasingly complex network of metabolic pathways would progressively be established. At the same time, the catalysts concerned would accumulate selectively to become choice substrates for elongation and other modifications that could enhance their efficiency, as well as their survival. Chemical evolution would thus proceed by a dual process of metabolic extension and catalytic innovation. Such a process should be largely deterministic and predictable from initial conditions.

Biochemical Phenomena↗
PubMed1979

Fate of plasma membrane during endocytosis. I. Uptake and processing of anti-plasma membrane and control immunoglobulins by cultured fibroblasts.

The uptake and processing by cultured rat embryo fibroblasts of control rabbit immunoglobulins (C IgG) or IgG directed against plasma membrane constituents (anti-PM IgG), and labeled with fluorescein (F) or with radioactive acetate (A), have been investigated by cell fractionation and immunological techniques. Both F and A anti-PM IgGs become bound to the cell surface, by a process that is slow, but largely temperature-independent. In the presence of an excess of high-affinity antibodies, binding reaches an absolute limit which corresponds to extensive coating of the plasma membrane. The anti-PM IgGs remain attached to the membrane for at least several days, even at 37 degrees C, with no significant transfer to lysosomes or degradation. In contrast, C IgGs are handled very differently by the fibroblasts, and their fate is strikingly affected by the type of labeling used. AC IgG is taken up slowly, at a rate proportional to its concentration, and is subsequently broken down in what appears to be lysosomes. Part of the AC IgG also binds to the plasma membrane. FC IgG is taken up many times faster than AC IgG, though with the same strict linearity as a function of concentration. Most of the FC IgG taken up is stored in cytoplasmic granules which behave like lysosomes. For reasons that are not understood, only about half of the stored FC IgG can be broken down. Cells exposed simulatnaously to AC IgG and FC IgG, or to A anti-PM IgG and FC IgG, handle each type of IgG in its characteristic fashion. Kinetic analysis of these results indicates that Ac IgG could be taken up by fluid endocytosis, but that FC IgG must be interiorized by a selective mechanism, presumably adsorptive in nature. That anti-PM antibodies remain stably bound to the plasma membrane and do not interfere with the uptake of FC IgG is interpreted to indicate either that two distinct membrane domains are involved in the two phenomena, or that membrane patches coated with anti-PM IgG participate in endocytosis, and are recycled back to the cell surface after delivering their contents intracellularly.

Animals↗
PubMed1979

Fate of plasma membrane during endocytosis. II. Evidence for recycling (shuttle) of plasma membrane constituents.

Cultured rat embryo fibroblasts were first allowed to store for 24 h fluorescein-labeled goat immunoglobulins directed against rabbit immunoglobulins (F anti-R IgG), and were subsequently exposed for 24 h to [(3)H]acetylated rabbit immunoglobulins known to bind to the cell membrane either specifically (anti-plasma membrane IgG: A anti-PM IgG) or unspecifically (contol IgG: AC IgG). As a result of immunological interaction between the two antibodies (no effect was found if the cells had been preloaded with control goat FC IgG), a substantial portion of the stored F anti-R IgG was unloaded from its intracellular storage site, appearing in the medium in the form of soluble immune complexes with rabbit A IgG. Part of the unloaded F anti-R IgG also was recovered in association with the plasma membrane, but only when A anti-PM IgG was used. In addition, significant reverse translocation of AC IgG from plasma membrane to lysosomes or some related intracellular storage compartment was also observed. With A anti-PM IgG, this translocation was less marked and affecte at the same time the plasma membrane marker 5'- nucleotidase. Cells that had stored horseradish peroxidase (HRP) simultaneously with F anti-R IgG did not unload HRP when exposed to A anti-PM IgG. These results support strongly, though not unequivocally, the concept that plasma membrane patches interiorized by endocytosis are recycled, or shuttled, back to the cell surface. In the framework of this concept, recycling antibody-coated membrane is taken to serve as vehicle for the selective intracellular capture and extracellular discharge of immunologically bound F anti-R IgG. The alternative explanation of regurgitation triggered off by immune complexes is considered less likely in view of the lack of HRP unloading.

Animals↗