The conformation of the mucopolysaccharides. Hyaluronates

X-ray-diffraction patterns of hyaluronate fibres from a variety of sources were obtained. Sodium hyaluronate gives well-defined patterns which index on a hexagonal unit cell with dimensions a=1.17+/-nm and a fibre repeat-distance of 2.85+/-0.03nm. A further form of sodium hyaluronate is produced by annealing at 60 degrees C in 75% relative humidity. This stable state indexes on a hexagonal unit cell of unchanged fibre repeat-distance but with a=1.87nm. The chain conformation is a threefold helix. Analysis of these diffraction patterns led to two tentative structures for sodium hyaluronate, involving different packing of the polysaccharide chains. The significance of side-chain interaction is discussed. Hyaluronic acid produces an X-ray pattern different from that obtained with the sodium salt. The fibre repeat-distance is 1.96+/-0.02nm and the unit cell appears to be monoclinic. The chain conformation is a twofold helix and conformational change between free acid and monovalent salt is discussed. These findings, together with model-building experiments, are interpreted as indicating a highly ordered structure, and the physical properties of hyaluronate solutions with regard to molecular shape and polyelectrolyte behaviour are rationalized.     

Isolation and Preliminary Characterization of Temperature-Sensitive Mutants of Rhizobiophage C

By using mutagenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine, 150 temperature-sensitive mutants of rhizobiophage c were isolated. All were able to form plaques at 14 C but not at 29 C. They were classified into 21 complementation groups. Representative temperature-sensitive mutants from each complementation group were analyzed with regard to gene function. The approximate time of expression of the genes defined by the mutants was measured by temperature-shift experiments. Most genes began to be expressed at 4.0 to 7.5 h after infection at 14 C. Four genes were found which were expressed 2.5 to 3.5 h after infection. Some mutants showed no DNA synthesis at 29 C; some showed a delay in lysis. Some produced apparently normal particles after infection and lysis at 29 C; others produced various types of defective particles. Some mutants showing no DNA synthesis at 29 C nevertheless caused lysis at the normal time together with the production of phage structural components. Representative mutants from each complementation group were mapped by using two-factor crosses. A preliminary genetic map of phage c was constructed from the data.     

Some Bacteriophages Active Against Rhizobium trifolii Strain W19

Fourteen soil bacteriophages active against Rhizobium trifolii W19 have been studied which fall into four structural groups. Group 1 phages have contractile tails. Some particles show double base plates to which at least three spikes are attached, and fibers are attached to the base plates. Group 2 phages also have contractile tails. At least five spikes are attached to the base plate, and there are spherical bodies adjacent to the tail, at the ends of fibers attached to the tail base. Group 3 phages have contractile tails, but are larger than phages of groups 1 and 2. The end of the tail has a complex structure. Group 4 phages have long, noncontractile tails.     

Diffusion and reaction of oxygen in the central tissue of ureide-producing legume nodules

Previous simulation models for the diffusion and reaction of oxygen in legume nodules were based on infected cells and neglected adjacent uninfected cells. This study uses a three-dimensional model of the central zone of legume nodules made up of the two cell types represented by a geometrically defined, space-filling, binary combination of polyhedra, each with bevelled edges to allow for a network of intercellular gas spaces. The model predicted a distinctively compartmentalized distribution of [O₂] between uninfected and infected cells; with high O₂ concentrations for an uninfected cell being consistent with, and necessary for, efficient operation of uricase and ureide synthesis and low O₂ concentrations across most of the infected cell providing a suitable environment for N₂-fixation. Compartmentalization of O₂ also predicted significant O₂ fluxes between cell types, compromising maintenance of low [O₂] in infected cells, as well as high [O₂] in uninfected cells. The results predict that there might be significant resistance to O₂ diffusion across the cell : cell interface due to the plasmalemma and cell walls.