Inhibition of liver fructose 1,6-bisphosphatase activity by Zn2+: Reversal by imidazole pyruvate

Summary Imidazole pyruvate was found to be a very potent natural chelating agent in reversing the inhibition of liver fructose 1,6-bisphosphatase activity by Zn²⁺. This metabolite may play a physiological role in gluconeogenesis.This work was supported by grant RR-8006 from the General Research Branch, Division of Research Resources, NIH, USA.     

Allotransplantation of rat parathyroid glands: Effects of organ culture and transplantation into the adrenal gland

Summary Allotransplantation of fresh, 1 or 2 week cultured parathyroid glands from Wistar rats (AgB²) to Fischer rats (AgB¹) resulted in prompt rejection of the transplant in the muscle site; whereas transplantation into the adrenal site offered slightly prolonged survival, suggesting that the latter is a privileged transplantation site.Acknowledgments. The authors thank Mrs Barbara Lovett for her secretarial assistance.     

Structure and bandgap closure in dense hydrogen

The possibility that steadily compressed hydrogen might undergo a transition from a proton-paired insulator to a monatomic metal was first suggested in 1935. But experimental realization of metallic hydrogen in solid form has remained elusive, despite studies at pressures as high as 342 GPa. The pairing structure is known to be robust (from the persistence of its associated vibron mode), leading to the suggestion of an alternative route to the metallic state, involving a band-overlap transition in which the pairing is preserved. Here we report density functional calculations within the local density approximation that predict a range of densities for hydrogen where a paired or molecular metallic state may be energetically preferred. The transition to this metallic state is naturally associated with the closing of an overall bandgap; but the pressures required to effect the transition are shown to change significantly when the gaps are corrected by approximate inclusion of many-electron effects. The implication is that a complete resolution of the structural and phase problem in dense hydrogen may require methods beyond the local density approximation.     

Cryptophyte algae are robbed of their organelles by the marine ciliate Mesodinium rubrum

Mesodinium rubrum (Lohmann 1908) Jankowski 1976 (= Myrionecta rubra) is a common photosynthetic marine planktonic ciliate which can form coastal red-tides. It may represent a 'species complex' and since Darwin's voyage on the Beagle, it has been of great cytological, physiological and evolutionary interest. It is considered to be functionally a phytoplankter because it was thought to have lost the capacity to feed and possesses a highly modified algal endosymbiont. Whether M. rubrum is the result of a permanent endosymbiosis or a transient association between a ciliate and an alga is controversial. We conducted 'feeding' experiments to determine how exposure to a cryptophyte alga affects M. rubrum. Here we show that although M. rubrum lacks a cytostome (oral cavity), it ingests cryptophytes and steals their organelles, and may not maintain a permanent endosymbiont. M. rubrum does not fall into recognized cellular or functional categories, but may be a chimaera partially supported by organelle robbery.     

Substance P-immunoreactive retinal ganglion cells and their central axon terminals in the rabbit

Retinal ganglion cells are the projection neurons that link the retina to the brain. Peptide immunoreactive cells in the ganglion cell layer (GCL) of the mammalian retina have been noted but their identity has not been determined. We now report that, in the rabbit, 25-35% of all retinal ganglion cells contain substance P-like (SP) immunoreactivity. They were identified by either retrograde transport of fluorescent tracers injected into the superior colliculus, or by retrograde degeneration after optic nerve section. SP immunoreactive cells are present in all parts of the retina and have medium to large cell bodies with dendrites that ramify extensively in the proximal inner plexiform layer. Their axons terminate in the dorsal lateral geniculate nucleus, superior colliculus and accessory optic nuclei, and these terminals disappear completely after contralateral optic nerve section and/or eye enucleation. In the dorsal lateral geniculate nucleus large, beaded, immunoreactive axons and varicosities make up a narrow plexus just below the optic tract, where they define a new geniculate lamina. The varicosities make multiple synaptic contacts with dendrites of dorsal lateral geniculate nucleus projection neurons and presumptive interneurons in complex glomerular neuropil. This is direct evidence that some mammalian retinal ganglion cells contain substance P-like peptides and strongly suggests that, in the rabbit, substance P (or related tachykinins) may be a transmitter or modulator in a specific population or populations of retinal ganglion cells.     

Hyperion's sponge-like appearance

Hyperion is Saturn's largest known irregularly shaped satellite and the only moon observed to undergo chaotic rotation. Previous work has identified Hyperion's surface as distinct from other small icy objects but left the causes unsettled. Here we report high-resolution images that reveal a unique sponge-like appearance at scales of a few kilometres. Mapping shows a high surface density of relatively well-preserved craters two to ten kilometres across. We have also determined Hyperion's size and mass, and calculated the mean density as 544 +/- 50 kg m(-3), which indicates a porosity of >40 per cent. The high porosity may enhance preservation of craters by minimizing the amount of ejecta produced or retained, and accordingly may be the crucial factor in crafting this unusual surface.