Roles of proteins in cation/membrane interactions of isolated rat cardiac sarcolemmal vesicles

To ascertain the roles of the membrane proteins in cation/sarcolemmal membrane binding, isolated rat cardiac sarcolemmal vesicles were extensively treated with Protease (S. aureus strain V.8). SDS-gel electrophoresis, protein and phosphate analysis confirmed that at least 20–22% of the protein, but none of the phospholipid, was solubilized by this procedure, and that the remaining membrane proteins were extensively hydrolyzed into small fragments. The cation binding properties of the treated vesicles were then examined by analyzing their aggregation behavior. The results demonstrate that this procedure had no effect on the selectivity series for di- and trivalent cation binding, or the divalent cation-induced aggregation behavior of the sarcolemmal vesicles at different pHs, indicating that proteins are probably not involved in these interactions and cannot be the low affinity cation binding sites previously observed [21, 22]. It did, however, change the pH at which protons induced sarcolemmal vesicle aggregation, suggesting a possible role for proteins in these processes. Protease treatment also modified the effects of fluorescamine labelling on divalent cation-induced vesicle aggregation, indicating that the NH, groups being labelled with fluorescamine are located on the sarcolemmal proteins. Together, these results support the hypothesis that di- and trivalent cation binding to the sarcolemmal membrane is largely determined by lipid/lipid and/or lipid/carbohydrate interactions within the plane of the sarcolemmal membrane, and that membrane proteins may exert an influence on these interactions, but only under very specialized conditions.Abbreviations MES 2-(N-morpholino)ethanesulfonic acid - MOPS 3-(N-morpholino) propanesulfonic acid - HEPES N-2-Hydroxyethylpiperizine-N-2- ethanesulfonic acid - CHES 2(N-Cyclohexylamino) ethanesulfonic acid - DTT DL-Dithiothreitol - PMSF Phenylmethyl-sulfonyl fluoride     

Synchronized endocytosis studied in the oocyte of a temperature-sensitive mutant of Drosophila melanogaster

Summary This study demonstrates that endocytosis in the oocyte of Drosophila melanogaster is reversibly blocked at the stage of pit formation by the temperature-sensitive, single-gene mutant, shibire ^ts1. Uptake of horseradish peroxidase conjugated with wheat-germ agglutinin was observed to be normal in mutant oocytes at 19°C, but was blocked at 29°C. After 10 min at 29°C, there was a build-up of coated pits along invaginations of the plasma membrane. Also, the endosomal compartment consisting of tubules, bulbs, and small yolk spheres, disappeared. Lowering the temperature to 19°C after 10 min at 29°C released a synchronized wave of endocytosis into a cytoplasm cleared of uptake-related organelles. By observing this synchronized wave after exposure to 19°C for varying durations, we determined that endocytosis proceeds as follows: coated pits/vesiclestubulessmall yolk spheresmature yolk spheres. The observations suggest that these organelles transform one into another within this sequence.     

An 83-kDa embryonic-type nuclear antigen is detected within the germinal vesicles of oocytes of the ascidianHalocynthia roretzi

Summary Monoclonal antibodies were raised against germinal vesicles which were isolated from fully grown oocytes of the ascidianHalocynthia roretzi. Immunoblot analyses revealed that one of the antibodies, designated Hgv-2, recognized a single band with a molecular weight of about 83 kDa. The antibody, visualized by indirect immunohistochemistry, reacted only with the germinal vesicles of oocytes and did not react with test cells, follicle cells, and other somatic cells of the gonad. During embryogenesis the antigenicity was found in interphase nuclei of all embryonic cells. The antibody did not react with chromosomes or the mitotic apparatus. The antigenicity was retained by interphase nuclei of larval cells, but it disappeared from nuclei of juveniles about 7 days after metamorphosis.     

Plant coated vesicles

Abstract. Coated vesicles are organelles frequently encountered in many plant cell types often in association with the plasma membrane, Golgi apparatus, partially coated reticulum and multivesicular bodies. They are readily identified by a characteristic cage or basket composed of interlocking triskelions of the protein clathrin which are bound to the surface of the vesicle membrane. Although their transport function has been well studied and characterized in mammalian systems, the possible importance of coated vesicles as transport organelles in plant cells is only just beginning to be explored. In this review, the authors describe the structure of higher plant coated vesicles and discuss their possible involvement in the endocytosis of marcromolecules, in exocytosis and in the intracellular transport of material between cytoplasmic compartments. Their possible role in maintaining the macromolecular composition of the plasma membrane whilst allowing recycling of excess lipid bilayer and their potential application as vehicles for the introduction of foreign macromolecules into plant cells are discussed.     

Identification of an insertion sequence, IS1081, in Mycobacterium bovis

Abstract: An insertion sequence, IS1081, in the genome of Mycobacterium bovis has been identified and sequenced. It is 1324 bp long with 15 bp inverted repeat ends and contains a large ORF. There are six copies of IS1081 in the genome of M. bovis and the element is also present in Mycobacterium tuberculosis . IS1081 is not closely related to other DNA elements described in actinomycetes but its putative transposase bears some resemblance to that of IS256 from Staphylococcus aureus . IS1081 may be useful for genetic manipulations and for developing a diagnostic test for bovine tuberculosis based on the polymerase chain reaction.     

Saponins can cause the agglutination of phospholipid vesicles

The interaction of saponins with phospholipid vesicles was investigated by means of liposomal agglutination or a precipitation assay. Ginsenoside-Rc, which has an α-l-arabinofuranose residue at the non-reducing terminus, exhibited remarkable agglutinability toward egg yolk phosphatidylcholine vesicles, while other saponins lacking this characteristic sugar residue showed less or no agglutinability. The molar ratio of ginsenoside-Rc to egg phosphatidylcholine in the aggregates was estimated to be 0.4–0.5 by a precipitation assay using ¹⁴C-labeled egg phosphatidylcholine vesicles. The agglutination was inhibited by p-nitrophenyl α-l-arabinofuranoside but not by p-nitrophenyl β-d-glucopyranoside or arabinogalactan. The results indicated that the α-l-arabinofuranose residue in ginsenoside-Rc should be important for the expression of the agglutinability. The agglutinability of ginsenoside-Rc toward lipid vesicles depended on both the polar head groups and fatty acyl chains of phospholipids. Egg yolk phosphatidylcholine vesicles were strongly agglutinated by ginsenoside-Rc, although sphingomyelin, phosphatidylethanolamine, phosphatidic acid and phosphatidylserine were less agglutinated. The agglutinability of ginsenoside-Rc was effective for phosphatidylcholines with short or unsaturated fatty acyl chains. The results suggested that the interaction of ginsenoside-Rc with phospholipid membranes should be affected not only by the chemical structure of the phospholipid but also by the membrane fluidity.     

Effects of osmotic conditions on ultrastructure of rat mammary epithelium

Summary Effects of osmotic conditions on secretion of milk serum were examined using standard transmission electron microscopy. Rat mammary glands were infused with hyper-, iso-, and hypo-osmotic solutions. The intramammary infusion of these agents elicited distinct and repeatable morphological responses from lactating epithelial cells. The response to hyperosmolarity was an increase in compound exocytotic figures and an increase in secretory vesicle size (¯x=1.65 m in diameter). Glands infused with hypo-osmolar solutions exhibited the opposite response; reduction in compound exocytotic figures and reduced vesicle size (¯x=0.34 n in diameter). The response to iso-osmotic solutions was indistinguishable from untreated control tissue. The ratio of vesicular projections to depressions (vesicle membrane/plasma membrane interactions) could be experimentally altered through the intramammary infusion of solutions with different osmotic potentials. These observations support the suggestion that osmotic conditions may influence exocytosis of milk serum.     

Bluelight-induced,flavin-mediated transport of redox equivalents across artificial bilayer membranes

Summary This paper continues our studies of physico-chemical properties of vesicle-bound flavins. Based on previous results, an advanced model system was designed in order to study the mechanisms underlying bluelight-induced redox transport across artificial membranes. The lumen of single-shelled vesicles was charged with cytochromec, and amphiphilic flavin (AF1 3, AF1 10) was bound to the membrane. Upon bluelight irradiation redox equivalents are translocated from exogeneous 1e ^–(EDTA)-and 2e ^–(BH₃CN^–) donors across the membrane finally reducing the trapped cytochromec both under aerobic and anaerobic conditions. The mechanisms involved are explored and evidence for the involvement of various redox states of oxygen, dihydroflavin and flavosemiquinone is presented.     

Characteristics of redox-linked proton ejection in cytochrome c oxidase reconstituted in phospholipid vesicles. New observations support mechanisms different from proton pumping

Experimental observations reveal a number of characteristics of the redox-linked proton ejection from cytochrome c oxidase vesicles, which apparently cannot be explained by a proton pumping activity of the oxidase. These observations seem, on the other hand, to provide useful elements for alternative explanation(s) of the proton ejection. It is proposed here that the process is scalar and not vectorial and can derive from redox-linked rupture of protonated salt-bridges in the oxidase-lipid complex.