Cell Surface Antigen Induced by Friend Murine Leukemia Virus Is also in the Virion

Intact particles of Friend leukemia virus derived from infectious mouse serum absorb only trace amounts of cytotoxic anti-FMR antibodies, but physical disruption of the virions by freezing and thawing, by ether extraction or by detergent treatment releases large amounts of FMR antigenic activity. Thus this antigen, previously considered to occur mainly as a neo-antigen on the surfaces of virus-infected cells and as a soluble substance in the serum of infected mice, may be primarily a virion component.     

Key structural features of the actin filament Arp2/3 complex branch junction revealed by molecular simulation

We investigated the structure, properties and dynamics of the actin filament branch junction formed by actin-related protein (Arp) 2/3 complex using all-atom molecular dynamics (MD) simulations based on a model fit to a reconstruction from electron tomograms. Simulations of the entire structure consisting of 31 protein subunits together with solvent molecules containing ～3 million atoms were performed for an aggregate time of 175 ns. One 75-ns simulation of the original reconstruction was compared to two 50-ns simulations of alternate structures, showing that the hypothesized branch junction structure is very stable. Our simulations revealed that the interface between Arp2/3 complex and the mother actin filament features a large number of salt bridges and hydrophobic contacts, many of which are dynamic and formed/broken on the timescale of the simulation. The simulations suggest that the DNase binding loops in Arp3, and possibly Arp2, form stabilizing contacts with the mother filament. Unbiased comparison of models sampled from the MD simulation trajectory with the primary experimental electron tomography data identified regions were snapshots from the simulation provide atomic details of the model structures and also pinpoints regions where the initial modeling based on the electron tomogram reconstruction may be suboptimal.     

Stimulation of lymphocyte receptor capping by the ionophore monensin

Summary The carboxylic ionophore monensin has a biphasic effect on antibody-induced Thy-1 cap formation. At higher concentrations, 5×10^–6–5×10^–5 m monensin causes a significant inhibition of receptor capping similar to that previously found with the Ca²⁺ selective ionophore A23187. At lower concentrations, 5×10^–8–5×10^–7 m capping is stimulated. It is concluded that capping at lower ionophore concentrations is a secific response to the ability of monensin to induce a rise in intracellular Na⁺, which indirectly elevates intracellular Ca²⁺ activity. This in turn activates the contractile machinery required for the aggregation of surface receptors into capped structures. At higher concentrations monensin acts as a nonspecific detergent, which causes detrimental structural alterations in some of the membrane components involved in the capping process.     

Proteolysis and amino acid recycling during nitrogen deprivation inSchizophyllum commune

Transfer of exponentially growing colonies ofSchizophyllum commune to nitrogen-deficient media for 6–60 h resulted in increased general proteolytic activity and decreased extractable protein when compared with controls. A concomitant increase in free radiolabeled leucine was detected in nitrogen-deprived colonies. Radiolabel was found in new surface hyphae following transfer of previously labeled colonies to media containing no label. The concentration of label present in the new growth indicates that this label is likely to have originated from proteolytic release of label from proteins in the older, central portions of the colony. The release of substantial amounts of label into the growth medium suggests that an extra-mycelial pathway may account, at least in part, for translocation of amino acids released by proteolysis.     

Effect of supersaturated aqueous hydrocortisone concentrations on the Δ1-dehydrogenase activity of free and immobilized Arthrobacter simplex

Supersaturated aqueous solutions of hydrocortisone have been prepared using hydrocortisone-poly(vinylpyrrolidone) (PVP) coprecipitates. Using these the hydrocortisone concentration in calcium alginate beads was increased severalfold. However, supersaturation reduced the Δ¹-dehydrogenase [3-oxosteroid:(acceptor) Δ¹-oxidoreductase, EC 1.3.99.4] activity of free and immobilized Arthrobacter simplex due to substrate inhibition. PVP coprecipitates may prove a useful tool for studying the effect of an increased soluble concentration of hydrophobic compounds in the absence of organic solvents.     

Enzymic interesterification of fats: Factors influencing the choice of support for immobilized lipase

Three grades of diatomaceous earth (Celite 560, Filtercel and Hyflo Supercel) and a controlled-pore silica have been examined for their suitability as support materials for lipase (triacyglycerol acylhydrolase, EC 3.1.1.3) catalysing the interesterification of fats. The controlled-pore silica gave a preparation with a low activity. Although all three Celites gave preparations with similar lipolytic activities, Hyflo Supercel gave the highest interesterification activity. The distribution of enzyme protein in Hyflo Supercel was examined by transmission electron microscopy.     

Large-Scale isolation of acid phosphatase from human erythrocytes

A laboratory process for the isolation of type B acid phosphatase from human erythrocytes has been scaled up 80 times. The enzyme was purified 1300-fold by adsorption on calcium phosphate gel, ammonium sulfate precipitation, and gel filtration. The yield was 27%. Results for the type A enzyme are also presented.