The function of fimbriae in Myxococcus xanthus. II. The role of fimbriae in cell-cell interactions.

Anti-fimbriae antiserum specifically inhibited swarming but no gliding motility per se in Myxococcus xanthus. However, formation of motile aggregates on agar and clumps in liquid media correlated with the presence of fimbriae. Ethylenediaminetetraacetic acid which inhibited swarming also inhibited fimbriae formation. Direct electron-microscopic observations revealed that fimbriae establish contact with apposing cell surfaces. Intact but not depolymerized fimbriae exhibited hemagglutination activity against guinea pig erythrocytes. This activity was inhibited by mannose, N-acetyl-D-galactosamine, and to a lesser degree by fructose, raffinose, melibiose, and alpha-methyl-D-mannoside. It is concluded that fimbriae are organelles which function to establish and maintain intercellular contacts, perhaps by a lectin-like function, during the coordinated movement of cell aggregates' (swarming) in myxobacteria. This hypothesis is supported by the observations of other workers that genes determining movement of cells in groups also control fimbriation in M. xanthus.     

The breakdown of Tetrahymena ribosomes in vivo. The effects of inhibitors.

1. When Tetrahymena were deprived of nutrients 50% of the polysomes disaggregated within 20 min and 20% of the total RNA broke down in 2 h. Ribosomal RNA accounted for 75% of the RNA breakdown. 2. RNA labelled by a long incubation with [14C]uridine was stable in growing cells and in the presence of actinomycin D, but broke down at the same rate as bulk RNA in starved cells. 3. The following substances inhibited the loss of RNA during starvation: cycloheximide (which inhibited both polysome disaggregation and protein synthesis), inhibitors of energy metabolism and puromycin (all of which caused polysome disaggregation and inhibited protein synthesis), and chloroquine and 7-amino-1-chloro-3-L-tosylamidoheptan-2-one ('TLCK') (neither of which affected polysomes or protein synthesis). 4. Starvation appears to activate a ribosome degradation mechanism that may involve lysosomal and non-lysosomal enzymes.     

The copper-molybdenum antagonism in ruminants. I. The formation of thiomolybdates in animal rumen

The formation of thiomolybdates, MoO_xS_4?x^2?(x = 0, 1, 2, or 3), from molybdate and sulphide salts in aqueous media has been studied under conditions which simulate the fluid phase in the rumen. The influences of the sulphide:molybdenum ratio, pH and phosphate levels on the nature of the species formed were investigated. The thiomolybdates, in particular the MoS_4^2? ion, have been implicated as the active intermediates in the widespread molybdenum induced copper deficiency that affects ruminants. The results presented here show that, under physiological conditions, di- and trithiomolybdates will form more readily than tetrathiomolybdate.     

The structure of water absorbed in collagen. I. The dielectric properties

The dielectric constant and the loss factor of water in collagen are measured for various water, NaCl, and HCl contents at frequencies ranging from 10² to 10⁵ Hz and at temperatures ranging from ?70° to +23°C. For all measurements, both the dielectric constant and the loss decrease monotonically as the frequency increases, or the temperature decreases; the absence of a maximum in the loss curves as a function of temperature and frequency indicates an extremely broad spectrum of relaxation times. By shifting the curves obtained for the dielectric constant and the loss factor along the log–frequency axis, all data, obtained at different temperatures, can be represented on master curves valid for 23°C. In order to explain these results, water molecules are assumed to be hydrogen bonded to each other in long chains. All water molecules in a chain can, cooperatively, be oriented in two different directions along the channel, resulting in large, reversible, dipole moments. These chains are not rigid, but are flexible liquid-like structures. Diffusion of chains as entities is assumed to be the rate-limiting step for dipole reorientation. Although the rate of diffusion decreases inversely proportional to chain length, the activation energy is independent of chain length. At lower temperatures, diffusion becomes slower, until at the glass point, approximately ?100°C, it ceases.