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Discusses and reviews the book `Regional Shopping Centres,' by P.J. McGoldrick and M.G. Thompson. Spatial switching of British retail capital to out-of-center locations; Strategies to block the `third wave' proposals.

We present new imaging of a sub-kpc-scale binary active galactic nucleus (AGN) candidate from the Karl G. Jansky Very Large Array (VLA) and the Multi-Element Radio Linked Interferometer Network (e-MERLIN). Two unresolved radio sources of similar luminosity around 1022 WHz−1 are identified in ∼35 h of e-MERLIN 6 cm imaging. These radio sources have an angular separation of 0.19 ± 0.06 arcsec and position angle (PA) of 22° ± 10°, corresponding to a projected separation of 0.95 ± 0.29 kpc at the epoch of the source. Our results suggest the presence of a kpc-scale active black hole pair hosted by two galaxies in the late stage of a merger at z  = 0.35. This work follows Woo et al. which presented two optical sources with a similar separation and PA, and a velocity separation of 200 km s−1. Our target adds to the currently limited sample of close-separation binary AGNs, which will aid in understanding the frequency of mergers and the stochastic gravitational wave background. [ABSTRACT FROM AUTHOR]

"This paper tackles the problem of handling uncontrolled heterogeneity due to unobserved influences on the decision process of spatial choice. It concentrates upon a discrete-time/'random-effects' approach to the problem of unobserved heterogeneity and documents parametric and non-parametric methods of specifying and estimating models which can cope with unobserved heterogeneity." The model is applied to data from Wales. (SUMMARY IN FRE), (excerpt)

Electron microscopic studies of chicken liver pyruvate carboxylase conducted under a variety of conditions show that this enzyme has an overall rhombic appearance and is comprised of four nonspherical subunits. The square planar tetramers originally identified by Valentine et al. (Valentine, R.C., Wrigley, N.G., Scrutton, M.C., Irias, J.J., and Utter, M.F. (1966) Biochemistry 5, 3111-3116) as pyruvate carboxylase have been shown to represent a minor protein contaminant found in many impure preparations of this enzyme. The contaminating protein has been separated from pyruvate carboxylase and further purified. It does not contain biotin and its constituent polypeptides are smaller than those of pyruvate carboxylase. This protein, whose function is not yet identified, shows a strong tendency to aggregate and is highly visible under many conditions of electron microscopy. Several lines of evidence support the thesis that the nonsquare tetramers are pyruvate carboxylase. When essentially homogeneous material is examined with a variety of different negative stains, numbers of intact molecules represent 20 to 70% of the visible protein. These tetramers, like pyruvate carboxylase, are very cold-labile and are protected from dissociation under these conditions by acetyl-CoA, a specific activator of this enzyme. Also, the structures form complexes with avidin and antibiotin antibody and thus, like pyruvate carboxylase, contain biotin.

Antibodies prepared against biotin linked to serum albumin have been purified by affinity chromatography using lipoyl-Sepharose (Harmon, F. (1980) Anal. Biochem. 103, 58-63). These antibodies have been used to study the structure of the biotin-containing enzyme, transcarboxylase, by examination of complexes with the enzyme using electron microscopy. The antibodies are observed complexed with the outer subunit of transcarboxylase, which contains the biotin, but they also combine with the central subunit which does not contain biotin. Addition of excess biotin does not prevent combination of the antibodies with the central subunit. Such nonspecific combination does not occur with the outer subunit which has been treated with avidin-Sepharose to remove the biotinyl subunit. Large insoluble intermolecular enzyme complexes are not observed, apparently because the divalent antibodies react with the multiple sites on a single transcarboxylase molecule or because the larger complexes are unstable. Combination of the antibodies with the enzyme weakens the intersubunit linkages, thus, when grids are prepared for electron microscopy, there frequently is much greater dissociation of the enzyme which is complexed than there is with the noncomplexed enzyme. The results have confirmed that the biotinyl subunits remain complexed with the outer subunits when transcarboxylase dissociates.

Deoxycholate-extracted rat liver gap junction was studied by high-resolution low-dose electron microscopy. Communicating channels between two adjoining cells supposedly form along the common axis of two apposed hexameric trans-membrane protein assemblies. These double hexamers are often arranged in large plaques on an ordered hexagonal net (8-9 nm lattice constant) and seem able to undergo structural alteration as a possible permeability control mechanism. Calcium is widely reported to uncouple gap junction, and we observed this alteration on exposure to Ca++ down to 10(-4) M concentration. When EGTA was added at matching concentrations, the alteration was reversible several times over one hour, but with considerable variability. It was imaged in the absence of any negative stain to avoid ionic and other complications. The resulting lack of contrast plus low-dose "shot" noise required digital Fourier filtering and reconstruction, but no detail was recovered below 1.8 nm. In other experiments with negative stain at neutral pH, gap junction connexons were apparently locked in the "closed" configuration and no transition could be induced. However, recovery of repeating detail to nearly 1.0 nm was possible, reproducibly showing a fine connective matrix between connexons . Whether this was formed by unfolded portions of the 28,000-dalton gap junction protein is not known, but its existence could explain the observed lattice invariance during the connexon structural transition.

The amino acid sequence of the adenovirus fibre protein reveals an approximately repeating motif of 15 residues. A diagonal comparison matrix established that these repeats extended from residue 43 to residue 400 of the 581 residue sequence. Assignment of secondary structure combined with model building showed that each 15-residue segment contained two short beta-strands and two beta-bends, one of which incorporated an extra residue in a beta-bulge of the Gx type. The 44 strands together gave a long (210 A) narrow, amphipathic beta-sheet, which could be stabilised by dimer formation to give the shaft of the fibre. The knob could arise from a dimer of the C-terminal 180 residue segment, predicted to be an 8-10 stranded beta-sandwich. This model is consistent with the electron micrographs of the fibre and it was supported by measurements of c.d. and of electron diffraction from microcrystals. The latter gave a pair of wide angle arcs, corresponding to a repeat of 4.7 A, oriented appropriately for a cross-beta structure. The relation of this structure to globular structures is discussed and a folding pathway is proposed. In its general features the structure resembles that proposed for the tail fibre of bacteriophage T4.

The molecular locations of antibody binding sites on the haemagglutinin of influenza virus X-31 were investigated by electron microscopy of haemagglutinin-monoclonal antibody complexes. Evidence was obtained for different sites of binding of different antibodies and direct correspondence was observed between these sites and the locations of antigenic sites A, B, and E (D. C. Wiley, I. A. Wilson, and J. J. Skehel (1981). Nature (London) 289, 373-378) defined by determining the amino acids recognized by the specific antibodies.

Influenza virus haemagglutinin mediates infection of cells by fusion of viral and endosomal membranes, triggered by low pH which induces a conformational change in the protein. We report studies of this change by electron microscopy, neutron scattering, sedimentation and photon correlation on X-31 (H3N2) haemagglutinin, both intact and bromelain cleaved, in various assemblies. HAs in all preparations showed a thinning at low pH, and a marked elongation which was removed on tryptic digestion, revealing altered features in the remaining stem portion of the molecule. A tentative model of the change is proposed, with reference to the known X-ray structure at neutral pH, in which major changes occur in the stem tertiary structure, while the top portion is only affected in its quaternary structure.

The Fab arms of immunoglobulin G (IgG) have long been known to hinge about their joint with the Fc subunit. Using monoclonal antibodies bound to influenza haemagglutinin (HA) as position markers, we now show that these arms can also rotate about their long axis with respect to Fc. We also show that when two IgGs are bound cyclically with two HA molecules, the arms can bend between the variable and constant domains to accommodate bond angle constraint.