“Active” conformation of an inactive semi-synthetic ribonuclease-S

We have studied the integrity of folded structure of a fully active semi-synthetic ribonuclease-S which lacks amino acid residues 16 through 20, and an inactive one with the same residues deleted and 4-fluoro-l-histidine substituted for active site histidine 12. Using “Y” form crystals, we obtained X-ray structural data to a resolution of 2·6 Å and, incorporating phase information calculated from refined ribonuclease-S coordinates, prepared several types of electron density maps. These showed that the overall backbone structure and active site configuration of both analogues do not differ noticeably from those of the native protein. Structural homology extends to the catalytically relevant side-chain at position 12; 4-F-His² assumes the same position as does His in active ribonuclease-S. This supports the view that the 4-F-Hisl2 analogue is inactive due to a change in histidine 12 imidazole basicity, rather than to any significant conformational distortion within the active site.     

Hypophysectomy increases the sensitivity of rats to naloxone-induced hypothermia

Three experiments were done to explore the role of pituitary endorphins in thermoregulation. Hypophysectomized rats were found to be hypothermic when compared to intact rats, but to show a hyperthermic response to handling-induced stress of equal magnitude to that seen in intact animals. In unstressed intact and hypophysectomized animals, the specific opiate antagonist, naloxone, produced a dose-dependent hypothermia, but hypophysectomized animals were found to be ten times more sensitive to naloxone than were the intact animals. In contrast, short-term blockade of pituitary endorphins by dexamethasone had no effect on the magnitude of the naloxone-inducted hypothermia. It was concluded that endorphins of pituitary origin play a long-term tonic role in the modulation of the sensitivity of the brain opioid systems.     

The population ecology of a natural population of the pierid butterfly Colias alexandra

Summary Key factor analysis techniques were used to examine factors determining the abundance of a population of non-pest Colias. The number of individuals entering each successive life stage in the sample population are summarized in life tables for 1975 to 1979. Survivorship to the adult is a relatively consistent proportionality (-x=1.2%, S.D.=1.14; 1975–1979). Factors resulting in reduced natality and, less importantly, mortality during larval diapause determine the population trends for C. alexandra. Egg mortality, pre-diapause larval mortality and postdiapause mortality contribute little to these trends. Possible key sources contributing to reduced natality are examined. Mortality of adults (including removal by collectors), poor weather conditions during the oviposition period, unseasonal snow or drought which affect nectar sources or oviposition sites are among the factors which cause reduced natality and result in population depression.     

Liver tissue graft rejection in murine major histocompatibility complex mutants

Liver tissue grafts between seven H-2 mutants and their parental strains have been studied. Each of these mutants was originally identified by reciprocal mutant—parental strain skin graft rejection. However, liver grafts among mutants and parental standard strains are not uniformly rejected. Liver graft rejection also fails to correlate with mutant—parental stimulation in CML and MLC. In addition, the immune reaction pattern of female mutant animals against grafts of male liver differs from the reaction pattern found in parental standard strains. Several explanations for the differences between immune response to liver and skin grafts are proposed, including different T cell subsets involved in recognition, availability of antigenic sites to immunocompetent cells, and structural differences between mutant and parental H-2 antigens. Abbreviations used in this paper: bml, 2, 3, 4,14; dml; fm2=mutants of strains C57BL/6, B10.D2 and B10.M respectively; B6=C57BL/6     

Cellular defense reactions of the shore crab, Carcinus maenas: in vivo hemocytic and histopathological responses to injected bacteria

The cellular defense reactions of the shore crab, Carcinus maenas, were studied, following injections of the bacteria Bacillus cereus and Moraxella sp., by histological and ultrastructural examination of the gills, heart, and hepatopancreas. The majority of the bacteria were sequestered to the gills, but some were also later evident in the heart and hepatopancreas. The presence of the bacteria in the gills initiated the formation of numerous small cell clumps, composed of both refractile and phagocytic cells, which entrapped many microorganisms. The clumps reached a maximum size 6 hr after inoculation and although some were cleared from the gills others persisted for 7 days, becoming more compact and necrotic during this period. Clump formation appears to occur following recognition of the bacteria as foreign and results in the hemocytes becoming sticky and adherent. The response is very effective in rapidly immobilizing the bacteria, thus restraining the spread of infection. It is proposed that this phenomenon may be a significant component of crustacean cellular host defenses.     

On functional morphology of the skeleton in lychnisc sponges (Porifera,Hexactinellida)

By comparison with architectural models it can be shown that both the “euretoid” arrangement of fused spicules and lychnisc node itself should enhance the strength of the skeleton of the Lychniscosa. Contrary to expectation however, the Lychniscosa do not inhabit more turbulent waters than the Hexactinosa with a simpler skeletal structure. Possible reasons for this are discussed.