The gut supports neurogenic differentiation of periocular mesenchyme, a chondrogenic neural crest-derived cell population

Periocular mesenchyme (PM) is a mesencephalic neural crest derived cell population which as a result of an interaction with the retinal pigment epithelium forms the scleral cartilage of the avian eye. Enteric neurons are derived from vagal crest cells which invade the gut. To study factors which regulate neuronal differentiation, we investigated whether the gut could direct neurogenesis in PM, a cell population that does not produce neurons in vivo. We report here that PM cultured in the presence of aneural chick hindgut on the chorioallantoic membrane (CAM), invaded the gut and formed large numbers of neurons. These were localized in enteric ganglia and contained neurofilament immunoreactivity, vasoactive intestinal peptide immunoreactivity, and somatostatin immunoreactivity. In the control PM cultured alone on the CAM, a small number of cells contained neurofilament immunoreactivity but lacked the appearance of mature neurons.     

Structural Properties and Features of Parasitic Bdellovibrio bacteriovorus

The structure of five parasitic strains of Bdellovibrio bacteriovorus was studied by electron microscope after negative staining and in shadow-case and etched freeze-fractured preparations. Special attention was paid to the cell wall and the flagellar sheath which is continuous with the wall or part of it. These structural components reveal distinct features which are induced by certain staining substances; they are exceedingly susceptible to disruption by physical treatments, and in old cells often appear impaired. In freeze-fractured cells the wall shows characteristic fracturing tendencies not known in other microorganisms. These structural properties and features are distinct to Bdellovibrio wall and flagellar sheath, the structural integrity of which is a fundamental requirement for the infectivity and survival of this organism. The anterior end of Bdellovibrio is differentiated: 6 to 12 ring-like structures (9 to 12 nm, outer diameter) are built into its wall and several fibers (7 to 10 nm wide, up to 1.5 μm long) emerge from it. Intracellular structures, which are revealed as compact oval bodies bulging from the cell border and have internal laminated organization, are characteristic of Bdellovibrio after negative staining with certain compounds. These findings on the structure of parasitic Bdellovibrio substantiate previous observations indicating the uniqueness of this organism and add criteria for the identification of this genus.     

Mediator structure and conformation change

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Regulation of glutaminase B in Escherichia coli. I. Purification, properties, and cold lability.

Escherichia coli contains two glutaminases, A and B, with pH optima below pH 5 and above pH 7, respectively. Neither glutaminase A nor B is released from E. coli by osmotic shock. Glutaminase B has been purified 6,000-fold and the purified preparation is estimated to contain about 40% glutaminase B. The enzyme has a molecular weight of 90,000 and an isoelectric point of 5.4. Glutaminase B exhibits a broad pH optimum between 7.1 and 9.0. Only L-glutamine is deamidated by glutaminase B, L-asparagine and D-glutamine are not deamidated. The substrate saturation curve for glutaminase B shows an intermediary plateau region. Like many regulatory enzymes, glutaminase B is cold-labile. The enzyme is inactivated by cooling and activated by warming; both processes are first order with respect to time. The activation energy for activation by warming was calculated to be 5900 cal/mol. Activation by warming increased the Vmax and decreased the S0.5 for L-glutamine, but did not alter the molecular weight of the catalytically active enzyme. Borate and glutamate protected glutaminase B from inactivation by cold.     

CLIX: a search algorithm for finding novel ligands capable of binding proteins of known three-dimensional structure.

A computer algorithm, CLIX, capable of searching a crystallographic data-base of small molecules for candidates which have both steric and chemical likelihood of binding a protein of known three-dimensional structure is presented. The algorithm is a significant advance over previous strategies which consider solely steric or chemical requirements for binding. The algorithm is shown to be capable of predicting the correct binding geometry of sialic acid to a mutant influenza-virus hemagglutinin and of proposing a number of potential new ligands to this protein.