Showing papers on "Cellular compartment published in 1986"

The trans Golgi Network: Sorting at the Exit Site of the Golgi Complex

Abstract: The Golgi complex is a series of membrane compartments through which proteins destined for the plasma membrane, secretory vesicles, and lysosomes move sequentially. A model is proposed whereby these three different classes of proteins are sorted into different vesicles in the last Golgi compartment, the trans Golgi network. This compartment corresponds to a tubular reticulum on the trans side of the Golgi stack, previously called Golgi endoplasmic reticulum lysosomes (GERL).

Effects of different transferrin forms on transferrin receptor expression, iron uptake, and cellular proliferation of human leukemic HL60 cells. Mechanisms responsible for the specific cytotoxicity of transferrin-gallium

Abstract: We have previously shown that human leukemic cells proliferate normally in serum-free media containing various transferrin forms, but the addition of transferrin-gallium leads to inhibition of cellular proliferation. Because gallium has therapeutic potential, the effects of transferrin-gallium on leukemic cell proliferation, transferrin receptor expression, and cellular iron utilization were studied. The cytotoxicity of gallium is considerably enhanced by its binding to transferrin and cytotoxicity can be reversed by transferrin-iron but not by other transferrin forms. Exposure to transferrin-gallium leads to a marked increase in cell surface transferrin binding sites, but despite this, cellular 59Fe incorporation is inappropriately low. Although shunting of transferrin-gallium to another cellular compartment has not been ruled out, other studies suggest that transferrin-gallium impairs intracellular release of 59Fe from transferrin by interfering with processes responsible for intracellular acidification. These studies, taken together, demonstrate that inhibition of cellular iron incorporation by transferrin-gallium is a prerequisite for inhibition of cellular proliferation.

Functional compartmentation of intracellular magnesium.

Abstract: Due to the distribution of Mg2+-binding ligands, such as DNA, RNA, or Mg2+-binding proteins, e.g. within the intermembranous space of mitochondria, intracellular magnesium is compartmentalized. Furthermore, cytosolic free Mg2+ is enriched at charged surfaces. Thus, the exact concentration of free intracellular Mg2+ can only be ascertained for a small volume element. Compartmentation of intracellular Mg2+ can also be determined by flux measurements with 28Mg2+. In different cell types, cellular Mg2+ is exchanged with different velocities, and, in some cell types, rapidly and slowly or non-exchangeable compartments are detectable. Cells can be Mg2+-depleted gradually by incubation with A23187 and EDTA. In cells which are Mg2+-depleted gradually, the Mg2+-dependent metabolic functions are inhibited in the following sequence: glycolysis, RNA, DNA synthesis, respiration, protein synthesis, protein synthesis appears to be the most sensitive function affected.

Nucleocytoplasmic interactions in the mouse embryo.

Abstract: Fertilized mammalian ova consist of haploid genomes derived from both parents and cytoplasmic components inherited largely from the female parent. These three cellular compartments must successfully interact with each other and with their environment for development to proceed. These interactions require the transposition of nuclear and cytoplasmic products between cellular compartments with resultant alteration of gene transcription and the cytoplasmic expression of preformed or newly synthesized gene products. We have investigated nuclear/cytoplasmic interactions in the mouse embryo via the microsurgical transfer of nuclei and cytoplasm. Experiments have specifically examined the ability of nuclei from later developmental stages or from a different species to support development, volume relationships between nuclear and cytoplasmic compartments, and the nonequivalency of the maternal and paternal genomic contributions to development. The ability of egg cytoplasm to alter the function of a variety of embryonic and adult nuclei and the ability of these nuclei to support development has been extensively tested in nuclear transplantation investigations in amphibian embryos.

A review of the study of protein secretion applying the protein A–gold immunocytochemical approach

Abstract: Exocrine and endocrine types of secretion were investigated in various cells by applying the protein A-gold immunocytochemical approach. Several proteins secreted by rat pancreatic and parotid acinar cells, mouse ameloblasts, rat pancreatic B cells and lymph-node plasma cells, and frog hepatocytes were studied using specific antibodies. While light microscope immunohistochemistry has allowed for good topographical identification of positive cells in tissues, the protein A-gold approach used at the electron microscope level has demonstrated the presence of specific antigenic sites in particular cellular compartments. All secretory proteins studied were detected in the rough endoplasmic reticulum, the Golgi apparatus, and the secretory granules of the corresponding secreting cells. In addition, some of the proteins were also found in lysosome-like structures. When good ultrastructural preservation of the cellular organelles was achieved, the labeling was revealed with very high resolution and precise localization. In such cases, we found labeling over transitional elements of the endoplasmic reticulum and in smooth vesicles in the Golgi area. The Golgi apparatus was subdivided into three compartments according to differences in labeling: the cisternae on the cisside, those of the trans-side and the trans-most rigid one. Quantitative evaluations of the intensities of labeling have allowed for 1) demonstration of the high specificity of the different labelings; 2) revelation of the existence of a gradient of increasing intensity that follows precisely the progress of the proteins along their secretory pathway; and 3) identification of intracellular sites where increments of protein antigenicity occur. Furthermore, they have revealed the existence of alterations in protein processing that occurred under experimental and pathological conditions. Double-labeling approaches were performed to demonstrate two different antigenic sites on the same tissue section by applying protein A-gold complexes formed by gold particles of different sizes. Protein A-gold immunocytochemistry has also been combined with cytochemical and radioautographic techniques. This review thus demonstrates that high-resolution quantitative immunocytochemistry can contribute significantly to the investigation of the intracellular processing of secretory proteins. It also illustrates the potential and versatility of the protein A-gold technique, which in combination with other procedures constitutes a powerful method in cell biology.

Intrazellulärer Transport in grünen Pflanzenzellen

Abstract: This report gives an overview of the functions of intracellular metabolite transport in a green plant cell. The phosphate translocator located in the inner membrane of the chloroplast envelope catalyzes the export of triose phosphate, the main product of photosynthesis, to the cytosol of the plant cell. For the reutilization of glycolate, the byproduct of photosynthesis, numerous transport processes across chloroplastic, peroxysomal and mitochondrial membranes are involved. During illumination, ATP and redox equivalents are delivered from the chloroplasts to the cytosol by the above mentioned phosphate translocator, in catalyzing a triosephosphate3-phosphoglycerate shuttle. Malate oxaloacetate shuttles between the chloroplastic, mitochondrial and peroxysomal spaces transfer redox equivalents between these cellular metabolic compartments. G rfinc Pflanzenzellen zeichnen sich gegen-fiber anderen eukaryontischen Zellen dadurch aus, dal3 ihr Stoffwechsel in besonders hohem MaDe kompartimentiert ist; diese Zellen weisen daher auch eine besonders hohe Anzahl von intrazellulfiren Transportvorgfingen auf. Es soll hier ein Uberblick fiber diese Transportvorg/inge gegeben werden.

Phosphorylation/dephosphorylation mechanisms in coated vesicles.

Abstract: Publisher Summary A major development in cell biology in the past few years has been the gradual realization of the magnitude of intracellular membrane traffic and the multiplicity of pathways for such traffic in various cells. These intracellular transfers of membranous proteins among discontinuous regions of membrane occur via the populations of vesicles. The chapter focuses on the specialized vesicular structures, the coated vesicles (CV), in relation to this intracellular traffic. The transfer of membranes and associated components among cellular compartments involves the vesiculation of one membrane bilayer and further fusion of the vesicle with another one. CV are widely involved in the first of these steps. The formation of a lattice-like coat from clathrin and associated proteins accompanies vesiculation. Clathrin-coated vesicles have been found to be involved in the transport of membranes and/or proteins along major established pathways. The kinase/phosphatase system associated to its specific pp50 substrate constitutes an extraordinary useful tool to study fundamental biochemical problems, such as protein–protein interactions, enzymatic regulation, and the molecular and physiological significance of protein phosphorylation. The different localization of the two antagonistic enzymatic activities amid the CV structure seems to indicate that pp50 plays an interface role between the membranous vesicle core and the clathrin coat.