Structural studies of lipophorin in insect blood by differential scanning calorimetry and 13C nuclear magnetic relaxation measurements. Location of hydrocarbons

The possible structure of lipophorin in insect blood (hemolymph) was investigated by differential scanning calorimetry (DSC) and 13C nuclear magnetic relaxation studies. The DSC heating curves of intact lipophorins showed endothermic peaks between -3 and 40 degrees C for lipophorins which contain hydrocarbons, whereas no such peaks were observed for lipophorins which do not contain this lipid. Hydrocarbon fractions isolated from the lipophorins showed endothermic peaks similar to those obtained from intact lipophorin in terms of the transition temperatures, the shapes, and the enthalpy changes. 13C spin lattice relaxation times of the (CH2)n resonance of hydrocarbons of intact lipophorin were measured as a function of temperature and revealed that the motions of hydrocarbon chains changed coincidentally with the onset and offset of phase transition. These data suggest the presence of a hydrocarbon-rich region within the lipophorin particles.     

Control of the activity of intracellular nucleases in Neurospora crassa.

Summary At least four species of nucleases (nuclease N₁, N₂, N₃ and N₄) and one ribonuclease (ribonuclease N₃) were detected in extract of wild type mycelia grown in high phosphate media by gel filtration of 0–65% ammonium sulfate precipitate through Sephadex G-100. Nuclease N₄ eluted the first is a latent nuclease, the activity of which is not detectable within a week after preparation of the extract but a significant increase in nuclease activity was observed during additional one or two weeks by standing the fraction at 4°C. Nuclease N₁ eluted the second is very labile and nuclease N₂ eluted the third is stable at the temperature. Nuclease N₃ eluted the last was activated within two or three weeks at 4°C. Although all the four nucleases were detected independent of the concentration of orthophosphate in culture media, significantly large amounts of latent ribonuclease (ribonuclease N₃) and a number of nucleases including at least one latent nuclease were observed in wild type mycelia grown in low phosphate media. Ribonuclease N₃ was determined to be a repressible enzyme. The activities of these constitutive latent nucleases, ribonuclease N₃ and a number of nucleases specifically present in wild type mycelia grown in low phosphate media were not observed or significantly reduced in both nuc-1 and nuc-2 mutants, which were deficient to derepress at least eight orthophosphate repressible enzymes relating to phosphate metabolism. A revertant from nuc-2 restored the ability to show activation of at least one of the constitutive latent nucleases.     

Enzymatic synthesis of amylose

Amylose is a linear polymer of α-1,4-linked glucose and is expected to be used in various industries as a functional biomaterial. However, pure amylose is currently not available for industrial purposes, since the separation of natural amylose from amylopectin is difficult. It is known that amylose has been synthesized using various enzymes. Glucan phosphorylase, together with its substrate, glucose-1-phosphate, is the most suitable system for the production of amylose since the molecular size of amylose can be controlled precisely. However, the problem with this system is that glucose-1-phosphate is too expensive for industrial purposes. This review summarizes our work on the enzymatic synthesis of essentially linear amylose, together with recent progress in the production of synthetic amylose using sucrose or cellobiose through the combined actions of phosphorylases.     

Glutathione maintenance is crucial for survival of melanocytes after exposure to rhododendrol

Rhododendrol is a phenolic compound that shows a tyrosinase‐dependent toxicity for melanocytes and occasionally induces a vitiligo‐like skin depigmentation. The post‐tyrosinase mechanisms determining melanocyte death or survival, however, are far from clear. Here, we find that rhododendrol treatment leads to a reduction in the levels of cellular glutathione but also induces a cellular antioxidant response that eventually increases glutathione levels. We further find that rhododendrol toxicity is enhanced when glutathione levels are experimentally reduced and alleviated when glutathione levels are increased. Hence, it appears that the size of the preexisting glutathione pool along with the capacity to supply glutathione via the antioxidant response determines whether melanocytes survive or die after rhododendrol exposure. It is conceivable, therefore, that rhododendrol‐induced leukoderma depends on the capacity to maintain appropriate glutathione levels and that enhancement of glutathione levels may preserve a patient's melanocytes and potentially help in repigmentation.     

Endothelin-1 binding to endothelin receptors in the rat anterior pituitary gland: possible formation of an ETA-ETB receptor heterodimer

1. Interaction in the recognition of endothelin-1 (ET-1), a typical bivalent ET receptor-ligand, between ET_A and ET_B receptors was investigated in the rat anterior pituitary gland, using our quantitative receptor autoradiographic method with tissue sections preserving the cell-membrane structure and ET receptor-related compounds.2. In saturation binding studies with increasing concentrations (0.77–200 pM) of ¹²⁵I-ET-1 (nonselective bivalent radioligand), ¹²⁵I-ET-1 binding to the rat anterior pituitary gland was saturable and single with a K _D of 71 pM and a B _max of 120 fmol mg^–1. When 1.0 M BQ-123 (ET_A antagonist) was added to the incubation buffer, binding parameters were 8.3 pM of K _D and 8.0 fmol mg^–1 of B _max, whereas 10 nM sarafotoxin S6c (ET_B agonist) exerted little change in these binding parameters (K _D, 72 pM; B _max, 110 fmol mg^–1).3. Competition binding studies with a fixed amount (3.8 pM) of ¹²⁵I-ET-1 revealed that when 1.0 M BQ-123 was present in the incubation buffer, ET_B receptor-related compounds such as sarafotoxin S6c, ET-3, IRL1620 (ET_B agonist), and BQ-788 (ET_B antagonist) competitively inhibited ¹²⁵I-ET-1 binding with K _is of 140, 18, 350 pM, and 14 nM, respectively, however, these compounds were not significant competitors for ¹²⁵I-ET-1 binding in the case of absence of BQ-123.4. In cold-ligand saturation studies with a fixed amount (390 pM) of ¹²⁵I-IRL 1620 (ET_B radioligand), IRL1620 bound to a single population of the ET_B receptor, and no change was observed in binding characteristics in the presence of 1.0 M BQ-123. ¹²⁵I-IRL1620 binding was competitively inhibited by ET-1 and ET-3 in the absence of BQ-123, with K _is of 20 and 29 pM, respectively, the affinities being much the same as those of 29 nM, in the presence of 1.0 M BQ-123.5. Two nonbivalent ET_A antagonists, BQ-123 and PD151242, were highly sensitive and full competitors for ¹²⁵I-ET-1 binding (5.0 pM), in the presence of 10 nM sarafotoxin S6c.6. Taken together with the present finding that mRNAs encoding the rat ET_A and the ET_B receptors are expressed in the anterior pituitary gland, we tentatively conclude that although there are ET_A and ET_B receptors with a functional binding capability for ET receptor-ligands, the ET_B receptor does not independently recognize ET-1 without the aid of the ET_A receptor. If this thesis is tenable, then ET-1 can bridge between the two receptors to form an ET_A–ET_B receptor heterodimer.     

Breast Milk Is Not a Significant Source for Early Epstein-Barr Virus or Human Herpesvirus 6 Infection in Infants: A Seroepidemiologic Study in 2 Endemic Areas of Human T-Cell Lymphotropic Virus Type I in Japan

In order to evaluate the possibility of Epstein-Barr virus (EBV) and human herpesvirus 6 (HHV-6) transmission via breast milk, a total of 331 serum specimens collected from bottle-fed and breast-fed children and their mothers, in 2 endemic areas of human T-cell lymphotropic virus type I (HTLV-I) in Japan, were assayed for antibodies to EBV and HHV-6. The seroprevalences of EBV and HHV-6 were over 95% both in the mothers of bottle-fed children and in those of breast-fed children. The seroprevalence of EBV at 12–23 months of age was 54.5% (36/66) and 55.8% (24/43) in breast-fed children and bottle-fed children, respectively. The seroprevalence of HHV-6 at 12–23 months of age was 90.9% (60/66) and 93.0% (40/43) in breast-fed children and bottle-fed children, respectively. No difference was observed between the seroprevalences of EBV and HHV-6 in breast-fed and bottle-fed children at 12–23 months of age. Our seroepidemiologic data indicate that breast milk is not a significant source of early EBV or HHV-6 infection in infancy.     

N′-[4-(dipropylamino)benzylidene]-2-hydroxybenzohydrazide is a dynamin GTPase inhibitor that suppresses cancer cell migration and invasion by inhibiting actin polymerization

Dynasore, a specific dynamin GTPase inhibitor, suppresses lamellipodia formation and cancer cell invasion by destabilizing actin filaments. In search for novel dynamin inhibitors that suppress actin dynamics more efficiently, dynasore analogues were screened. N′-[4-(dipropylamino)benzylidene]-2-hydroxybenzohydrazide (DBHA) markedly reduced in vitro actin polymerization, and dose-dependently inhibited phosphatidylserine-stimulated dynamin GTPase activity. DBHA significantly suppressed both the recruitment of dynamin 2 to the leading edge in U2OS cells and ruffle formation in H1299 cells. Furthermore, DBHA suppressed both the migration and invasion of H1299 cells by approximately 70%. Furthermore, intratumoral DBHA delivery significantly repressed tumor growth. DBHA was much less cytotoxic than dynasore. These results strongly suggest that DBHA inhibits dynamin-dependent actin polymerization by altering the interactions between dynamin and lipid membranes. DBHA and its derivative may be potential candidates for potent anti-cancer drugs.     

Random walk in genome space: A key ingredient of intermittent dynamics of community assembly on evolutionary time scales

Community assembly is studied using individual-based multispecies models. The models have stochastic population dynamics with mutation, migration, and extinction of species. Mutants appear as a result of mutation of the resident species, while migrants have no correlation with the resident species. It is found that the dynamics of community assembly with mutations are quite different from the case with migrations. In contrast to mutation models, which show intermittent dynamics of quasi-steady states interrupted by sudden reorganizations of the community, migration models show smooth and gradual renewal of the community. As a consequence, instead of the 1/f diversity fluctuations found for the mutation models, 1/f², random-walk like fluctuations are observed for the migration models. In addition, a characteristic species-lifetime distribution is found: a power law that is cut off by a “skewed” distribution in the long-lifetime regime. The latter has a longer tail than a simple exponential function, which indicates an age-dependent species-mortality function. Since this characteristic profile has been observed, both in fossil data and in several other mathematical models, we conclude that it is a universal feature of macroevolution.