Lipid-polyethylene glycol interactions: I. Induction of fusion between liposomes

Summary Fusion between unilamellar vesicles of both egg phosphatidylcholine and bovine phosphatidylserine was induced by polyethylene glycol. Aggregation and fusion events were monitored by electron microscopy and turbidity measurements. The threshold concentration of polyethylene glycol for aggregation and fusion is found to be independent of lipid concentration. Typically, aggregation of phosphatidylcholine vesicles starts at 2.5% (wt/wt) polyethylene glycol, but fusion is not significant until the polyethylene glycol concentration reaches 35%. Multilamellar vesicles were formed as a result of fusion.Abbreviations PEG Polyethylene glycol - IMP Intramembranous particle - PC Phosphatidylcholine - PS Phosphatidylserine - SUV Small unilamellar vesicles - MLV Multilamellar vesicles - DPPC Dipalmitoyl phosphatidylcholine - DSC Differential scanning calorimetry     

Lipid-polyethylene glycol interactions: II. Formation of defects in bilayers

Summary Polyethylene glycol, a known cell fusogen, is found to induce the formation of structural defects in egg phosphatidylcholine multilamellar vesicles, as shown by freeze-fracture microscopy.³¹P NMR spectra of these vesicles reveal the existence of a nonbilayer (isotropic) phase. The observed disruption in the bilayers is believed to be associated with an intermediate stage of membrane fusion.Abbreviations PEG Polyethylene glycol - IMP Intramembranous particle - PC Phosphatidylcholine - PS Phosphatidylserine - SUV Small unilamellar vesicles - MLV Multilamellar vesicles - DPPC Dipalmitoyl phosphatidylcholine - DSC Differential scanning calorimetry - DMPC Dimyristoylphosphatidylcholine - T _c Phase transition temperature     

Modifiable chromatophore proteins in photosynthetic bacteria.

The chromatophores of Chromatium vinosum, as well as six other photosynthetic bacteria, contained two or more proteins which were insoluble when heated in the presence of sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (beta-ME). When the chromatophores were dissolved at room temperature in SDS-beta-ME, these proteins were present in the SDS-polyacrylamide gel electrophoresis profiles, but when the samples were dissolved at 100 degrees C, they were absent or considerably diminished. When one-dimensional gels of chromatophores solubilized at room temperature were soaked in the SDS-beta-ME solution and heated to 100 degrees C and the gels were run in a second dimension, the proteins became immobilized in the original first-dimension gel, where they could be detected by staining. The two major proteins so affected in C. vinosum had apparent molecular weights of 28,000 and 21,000. The chromatophores of several other photosynthetic bacteria also contained predominant proteins between 30,000 and 19,000 molecular weight, which became insoluble when heated in the presence of SDS and beta-ME. In at least two of the species examined, these appeared to be reaction center proteins. The conditions causing the proteins to become insoluble were complex and involved temperature, SDS concentration, and the presence of sulfhydryl reagents. The chromatophores of four of the Chromatiaceae species and two strains of one of the Rhodospirillaceae species examined had a protein-pigment complex that was visible in SDS-polyacrylamide gel profiles of samples dissolved at room temperature but was absent in samples dissolved at 100 degrees C.     

Nitrogen control of Salmonella typhimurium: co-regulation of synthesis of glutamine synthetase and amino acid transport systems.

Nitrogen control in Salmonella typhimurium is not limited to glutamine synthetase but affects, in addition, transport systems for histidine, glutamine, lysine-arginine-ornithine, and glutamate-aspartate. Synthesis of both glutamine synthetase and transport proteins is elevated by limitation of nitrogen in the growth medium or as a result of nitrogen (N)-regulatory mutations. Increases in the amounts of these proteins were demonstrated by direct measurements of their activities, by immunological techniques, and by visual inspection of cell fractions after gel electrophoresis. The N-regulatory mutations are closely linked on the chromosome to the structural gene for glutamine synthetase, glnA: we discuss the possibility that they lie in a regulatory gene, glnR, which is distinct from glnA. Increases in amino acid transport in N-regulatory mutant strains were indicated by increased activity in direct transport assays, improved growth on substrates of the transport systems, and increased sensitivity to inhibitory analogs that are trnasported by these systems. Mutations to loss of function of individual transport components (hisJ, hisP, glnH, argT) were introduced into N-regulatory mutant strains to determine the roles of these components in the phenotype and transport behavior of the strains. The structural gene for the periplasmic glutamine-binding protein, glnH, was identified, as was a gene argT that probably encodes the structure of the lysine-arginine-ornithine-binding protein. Genes encoding the structures of the histidine- and glutamine-binding proteins are not linked to glnA or to each other by P22-mediated transduction; thus, nitrogen control is exerted on several unlinked genes.     

Control of concanavalin A receptor mobility by cytoplasmic actin in human tumour cells.

Tissue culture monolayers of seven human intracranial tumours comprising 2 astrocytomas, 3 meningiomas, 1 secondary squamous cell carcinoma and 1 secondary adenocarcinoma were examined by a double immunofluorescent staining technique to demonstrate Concanavalin A (Con A) surface receptors and cytoplasmic actin in the same cell. Tumour cells, treated with fluoresceinisothiocyanate-labelled Con A (FITC-Con A) showed staining in cell margins or in a random distribution over the cell surface. Incubating the cells with FITC-Con A at 37 degrees for increasing periods of time resulted first in staining of clusters and later of perinuclear globules. Cells, pretreated with 4% paraformaldehyde at 4 degrees for 10 min or with cytochalasin B at 37 degrees for 30 min showed staining restricted to cell margins. In the cytochalasin B-treated cells, the peripheral staining was in the form of coarse clusters. Double fluorochrome studies showed that the anti-actin antibody (AAA) staining occurred in sites closely related to those stained by FITC-Con A both in untreated as well as in cytochalasin B-treated cells. The findings suggest that Con A receptors, as an example of a stable cell membrane determinant in human tumour cells, are associated with actin and that their mobility on the cell surface is dependent on an intact cytoplasmic actin system.     

A new compound, 21α-hydroxyfriedel-4(23)-en-3-one and other triterpenoids from Phyllanthus reticulatus

The petrol extracts of the stems and leaves of Phyllanthus reticulatus both gave friedelin and sitosterol, and that of the former also friedelan-3β-ol, glochidonol, 21α-hydroxyfriedelan-3-one and a new compound, which was proved to be 21α-hydroxyfriedel-4(23)-en-3-one. The ethanol extract of the stems yielded betulinic acid.     

Nucleic acid metabolism in cold-treated wheat embryos

The incorporation of ₃₂P into nucleic acid fractions separatedon a MAK column was compared for normally germinated and cold-treatedwheat embryos. ₃₂P accumulation in DNA fraction was decreasedby cold treatment, although that in the RNA fractions was slightlypromoted. The synthesis of the fraction, probably mRNA, elutedafter the peak of heavy rRNA was enhanced in cold-treated embryosand suppressed when the embryos were cold-treated in the presenceof 8-azaguanine, an inhibitor of vernalization. (Received May 2, 1975; )     

Changes in nucleic acids, protein-nitrogen and amino-nitrogen of excised winter wheat embryos during vernalization

Embryos excised from winter wheat grains were vernalized for10–50 days with or without sugar (sucrose). Determinationswere made of fresh weight, protein-nitrogen, amino-nitrogen,RNA and DNA. There was no change in the contents of RNA of wheatembryos during the vernalization. The incorporation of ³²P intonucleic acid in wheat embryos during vernalization in the presenceof sugar was much higher than that of embryos vernalized withoutsugar. From these results we assumed that RNA turnover occurredduring the vernalization. There was no significant differencein the nucleotide composition of RNA extracted between the vernalizedand unvernalized embryos. The RNA of wheat embryos was separatedinto two fractions. Proportions of these two RNA fractions variedin the course of cold treatment, and similar changes were foundin developing wheat leaves. (Received July 25, 1974; )     

Fetal monitoring during maternal cardiac surgery with cardiopulmonary bypass.

Fetal cardiac activity was monitored with an external ultrasound transducer in two patients with clinical class III heart disease due to severe mitral stenosis complicated by pulmonary hypertension, undergoing open heart surgery with cardiopulmonary bypass in the 2nd trimester of pregnancy. Fetal distress was detected in one patient, who had mitral valvuloplasty, and was corrected by increasing the rate of blood flow, and the other patient had a mitral valve replacement but no fetal distress was noted. The postoperative course of both mothers and fetuses was uneventful.