Structural analysis of membranes by means of a nuclear reaction

A narrow nuclear resonance in low-energy proton-induced nuclear reactions in the stable isotope ¹⁸O has been utilized in a new technique for investigating the structure of biological membranes. This technique leads to a direct determination of the density profile of ¹⁸O-labelled molecules.Results with a multilayer of egg lecithin and with erythrocyte ghosts demonstrate the applicability of the method to structural analysis.     

A New Species of Acrodipsas Sands (Lepidoptera: Lycaenidae) from Inland New South Wales and Southern Queensland

Acrodipsas mortoni sp.n. from inland New South Wales and southern Queensland is described, figured, contrasted with the related A. arcana (Miller and Edwards) and assigned to the illidgei species-group.     

Increase in lipid microviscosity of unilamellar vesicles upon the creation of transmembrane potential

Summary Diffusion potential of potassium ions was formed in unilamellar vesicles of phosphatidyl choline. The vesicles, which included potassium sulfate buffered with potassium phosphate, were diluted into an analogous salt solution made of sodium sulfate and sodium phosphate. The diffusion potential was created by the addition of the potassium-ionophore, valinomycin. The change in lipid microviscosity, ensuing the formation of membrane potential, was measured by the conventional method of fluorescence depolarization with 1,6-diphenyl-1,3,5-hexatriene as a probe. Lipid microviscosity was found to increase with membrane potential in a nonlinear manner, irrespective of the potential direction. Two tentative interpretations are proposed for this observation. The first assumes that the membrane potential imposes an energy barrier on the lipid flow which can be treated in terms of Boltzmann-distribution. The other interpretation assumes a decrease in lipid-free volume due to the pressure induced by the electrical potential. Since increase in lipid viscosity can reduce lateral and rotational motions, as well as increase exposure of functional membrane proteins, physiological effects induced by transmembrane potential could be associated with such dynamic changes.     

Binding of ADP to beef-heart mitochondrial ATPase (F1)

1. ADP binding to beef-heart mitochondrial ATPase (F1), in the absence of Mg2+, has been determined by separating the free ligand by ultrafiltration and determining it in the filtrate by a specially modified isotachophoretic procedure. 2. Since during the binding experiments the 'tightly' bound ADP (but not the ATP) dissociates, it is necessary to take this into account in calculating the binding parameters. 3. The binding data show that only one tight binding site (Kd about 0.5 microM) for ADP is present. 4. It is not possible to calculate from the binding data alone the number of or the dissociation constants for the weak binding sites. It can be concluded, however, that the latter is not less than about 50 microM.     

Isolation and characterization of an insulin-degrading enzyme from Drosophila melanogaster

An insulin-degrading enzyme (IDE) from the cytoplasm of Drosophila Kc cells has been purified and characterized. The purified enzyme is a monomer with an s value of 7.2 S, an apparent Km for porcine insulin of 3 microM, and a specific activity of 3.3 nmol of porcine insulin degraded/(min.mg). N-Terminal sequence analysis of the gel-purified enzyme gave a single, serine-rich sequence. The Drosophila IDE shares a number of properties in common with its mammalian counterpart. The enzyme could be specifically affinity-labeled with [125I]insulin, has a molecular weight of 110K, and has a pI of 5.3. Although Drosophila Kc cells grow at room temperature, the optimal enzyme activity assay conditions parallel those of the mammalian IDE: 37 degrees C and a pH range of 7-8. The Drosophila IDE activity, like the mammalian enzymes, is inhibited by bacitracin and sulfhydryl-specific reagents. Similarly, the Drosophila IDE activity is insensitive to glutathione as well as protease inhibitors such as aprotinin and leupeptin. Insulin-like growth factor II, equine insulin, and porcine insulin compete for degradation of [125I]insulin at comparable concentrations (approximately 10(-6) M), whereas insulin-like growth factor I and the individual A and B chains of insulin are less effective. The high degree of evolutionary conservation between the Drosophila and mammalian IDE suggests an important role for this enzyme in the metabolism of insulin and also provides further evidence for the existence of a complete insulin-like system in invertebrate organisms such as Drosophila.     

Virulent strains of Vibrio vulnificus isolated from estuaries of the United States West Coast

Vibrio vulnificus was isolated from United States West Coast estuaries at a low frequency (5.9%) from 529 samples of water, shellfish, and sediment. Four strains tested with iron-treated mice had 50% lethal dose values ranging from 7.6 to 360 CFU, compared with a 50% lethal dose of 4.9 CFU for a clinical isolate that caused the death of a septicemic patient. The presence of this pathogen may be a hazard to users of marine beaches and consumers of raw shellfish on the West Coast, especially to persons most susceptible to V. vulnificus septicemia. Species-specific antiflagellar serum and a gene probe for cytotoxin-hemolysin production were useful for screening these environmental isolates.     

A derivative of Zymomonas mobilis ATCC 10988 with impared ethanol production

Summary A derivative of Zymomonas mobilis ATCC 10988 has been isolated from cells treated with acridine orange. This derived strain, designated CU1, was found to have markedly decreased ethanol production and concomitant glucose utilisation capabilities when grown on high concentrations of glucose. Additionally, it was found that CU1 had altered alcohol dehydrogenase activity and also lacks at least one of the natural plasmids of Z.mobilis, the 3kb species.