Inhibition of geranylgeranyl diphosphate synthesis in in vitro systems

The incorporation of [¹⁴C]mevalonate and [¹⁴C]isopentenyl diphosphate into geranylgeranyl diphosphate was investigated in in vitro systems from Cucurbita pepo (pumpkin) endosperm and from Avena sativa etioplasts. Mevalonate incorporation was effectively inhibited in the pumpkin system by geranylgeranyl diphosphate and geranylgeranyl monophosphate but less effectively by phytyl diphosphate or inorganic diphosphate. Membrane lipids, geranyllinalool, or lecithin enhanced mevalonate incorporation in the Cucurbita system. Incorporation of isopentenyl diphosphate was also enhanced by lecithin and inhibited by geranylgeranyl diphosphate in the Cucurbita system. No lipid enhancement was found in the Avena system; inhibition by GGPP required a much higher GGPP concentration than in the Cucurbita system.     

Optimum utilization of sewage sludge of low and high metal content for grain production on arid lands

Summary Two municipal sludges, one from a highly industrialized city, Chicago, Il, and another from a little industrialized, highly agricultural area, Tucson, AZ are compared for winter barley production on Pima c 1 (Typic torrifluvent). Both sludges were responsible for highly significant additions of Zn, Cu, Ni, Cd and P to the soil each year when applied at the rates of 100 mt/ha singly and 20 mt/ha each year for 4 years. Nitrogen responses for barley straw and grain were observed from both sludges. Tucson sludge appears to be attractive as a potential fertilizer, not only as an NPK source, but also for its organic matter and minimal amounts of heavy metals. The Chicago sludge with relatively high levels of heavy metals, particularly Cd, appears poorly suited as a fertilizer, if used for an extended period of time, because of the plant's tendency to take up elevated levels of certain heavy metals. Some parts of barley plants proved to be a better indicator of heavy metal uptake and concentration than others. The diagnostic-tissue test promises to be a useful tool to warn against undesirable accumulation of heavy metals. Fortunately, when compared with other plant parts, the heavy metal in grain was the least altered as a result of continued sewage sludge use on arid land. The soil's neutral to slightly alkaline pH and the presence of lime throughout the soil profile appeared to be critical factors in keeping plant uptake of heavy metals relatively low as compared with soils of other climates.     

Temporal dynamics of estuarine phytoplankton: A case study of San Francisco Bay

Detailed surveys throughout San Francisco Bay over an annual cycle (1980) show that seasonal variations of phytoplankton biomass, community composition, and productivity can differ markedly among estuarine habitat types. For example, in the river-dominated northern reach (Suisun Bay) phytoplankton seasonality is characterized by a prolonged summer bloom of netplanktonic diatoms that results from the accumulation of suspended particulates at the convergence of nontidal currents (i.e. where residence time is long). Here turbidity is persistently high such that phytoplankton growth and productivity are severely limited by light availability, the phytoplankton population turns over slowly, and biological processes appear to be less important mechanisms of temporal change than physical processes associated with freshwater inflow and turbulent mixing. The South Bay, in contrast, is a lagoon-type estuary less directly coupled to the influence of river discharge. Residence time is long (months) in this estuary, turbidity is lower and estimated rates of population growth are high (up to 1–2 doublings d^–1), but the rapid production of phytoplankton biomass is presumably balanced by grazing losses to benthic herbivores. Exceptions occur for brief intervals (days to weeks) during spring when the water column stratifies so that algae retained in the surface layer are uncoupled from benthic grazing, and phytoplankton blooms develop. The degree of stratification varies over the neap-spring tidal cycle, so the South Bay represents an estuary where (1) biological processes (growth, grazing) and a physical process (vertical mixing) interact to cause temporal variability of phytoplankton biomass, and (2) temporal variability is highly dynamic because of the short-term variability of tides. Other mechanisms of temporal variability in estuarine phytoplankton include: zooplankton grazing, exchanges of microalgae between the sediment and water column, and horizontal dispersion which transports phytoplankton from regions of high productivity (shallows) to regions of low productivity (deep channels).Multi-year records of phytoplankton biomass show that large deviations from the typical annual cycles observed in 1980 can occur, and that interannual variability is driven by variability of annual precipitation and river discharge. Here, too, the nature of this variability differs among estuary types. Blooms occur only in the northern reach when river discharge falls within a narrow range, and the summer biomass increase was absent during years of extreme drought (1977) or years of exceptionally high discharge (1982). In South Bay, however, there is a direct relationship between phytoplankton biomass and river discharge. As discharge increases so does the buoyancy input required for density stratification, and wet years are characterized by persistent and intense spring blooms.     

Proton nuclear magnetic resonance study of N,N-diethylformamide exchange on (N,N-diethylformamide)2,2′2″-tris(dimethylamino)triethylamine)cobalt(II) and its copper(II) analogue

Proton NMR studies of N,N-diethylformamide (def) exchange on [M(Me₆tren)def]²⁺ where M = Co and Cu yield: k_ex (298.2K) = 26.3 ± 2.2, 980 ± 70 s⁻¹; ΔH^≠ = 58.3 ± 1.7, 36.3 ± 0.9 kJ mol⁻¹; ΔS^≠= −22.2 ± 4.6, −65.9 ± 2.5 J K⁻¹ mol⁻¹; and ΔV^≠ = −1.3 ± 0.2, 5.3 ± 0.3 cm³ mol⁻¹ respectively. These data which are consistent with a and d activation modes operating when M = Co and Cu respectively are compared with data for related systems.     

Cell surface influenza haemagglutinin can mediate infection by other animal viruses.

We have used filter-grown Madin-Darby canine kidney (MDCK) cells to explore the mechanism by which influenza virus facilitates secondary virus infection. Vesicular stomatitis virus (VSV) and Semliki Forest virus (SFV) infect only through the basolateral surface of these polarized epithelial cells and not through the apical surface. Prior infection with influenza virus rendered the cell susceptible to infection by VSV or SFV through either surface. The presence of both a permissive and a restrictive surface for virus entry in the same cell allowed us to determine how the influenza infection enhanced the subsequent infection of a second virus. Biochemical and morphological evidence showed that influenza haemagglutinin on the apical surface serves as a receptor for the superinfecting virus by binding to its sialic acid-bearing envelope proteins. Influenza virus also facilitates secondary virus infection in non-epithelial cells; baby hamster kidney cells (BHK-21), which are normally resistant to infection by the coronavirus (mouse hepatitis virus MHV-A59), could be infected via the haemagglutinin-sialic acid interaction. Facilitation of secondary virus infection requires only the sialic acid-binding properties of the haemagglutinin since the uncleaved haemagglutinin could also mediate virus entry.     

Expression of monoclonal antibody-defined cell surface antigens during rat brain development

Using single-cell suspensions of mechanically dissociated, prenatal BDIX-rat brain cells (13th, 15th, and 21st days after fertilization) for immunization, we have established a collection of 37 monoclonal antibodies (Mabs) directed against neural cell surface determinants. The developmental-stage-dependent expression of cell-surface antigens recognized by these Mabs was analyzed both on plasma membranes isolated from whole brains of BDIX rats (prenatal days 13-22 and adults) using an indirect 125I solid-phase radioimmunoassay, and on intact BDIX-rat brain cells (prenatal days 13-22) using a fluorescence-activated cell sorter. Different types of developmental stage-dependent profiles of Mab binding were found, these being indicative of the presence of neural cell surface determinants whose expression increases, decreases, or does not change with brain development. Some of the Mab-binding profiles showed transient changes as a function of developmental stage. These Mabs are currently being used for the characterization, reproducible identification, and isolation of neural cell subpopulations of the developing rat brain, with the aim of investigating the cell type dependence and developmental (differentiation) stage dependence of malignant transformation following pulse exposure to the carcinogen N-ethyl-N-nitrosourea at defined stages of brain development.     

l- andd-alanine transport in brush border membrane vesicles from lepidopteran midgut: Evidence for two transport systems

Summary In brush border membrane vesicles from the midgut ofPhilosamia cynthia larvae (Lepidoptera) thel- andd-alanine uptake is dependent on a potassium gradient and on transmembrane electrical potential difference. Each isomer inhibits the uptake of the other form: inhibition ofl-alanine uptake byd-alanine is competitive, whereas inhibition ofd-alanine uptake byl-alanine is noncompetitive. Transstimulation experiments as well as the different pattern of specificity to cations suggest the existence of two transport systems. Kinetic parameters for the two transporters have been calculated both when K_out>K_in and K_out=K_in.d-alanine is actively transported also by the whole midgut, but it is not metabolized by the intestinal tissue.     

Activation of tyrosinase in mouse melanoma cell cultures

Summary Tyrosinase activity increased in Cloudman S-91 mouse melanoma cell homogenates incubated at 37°C for a minimum of 8 h. Enzyme activity continued to increase for 48h at which time the maximal level of activation was observed. Activation did not occur at 4°C and did not occur in the cytosol fraction of the cell, suggesting that the response was localized to melanosomes. The activated enzyme was resistant to solubilization with the nonionic detergent, Triton X-100, and preparation of homogenates in this detergent did not inhibit the temperature-dependent activation of the melanosomal fraction of the cell. The activation process increased the V _Max of tyrosinase 10-fold and lowered the K _M by a factor of 2 as determined by the tyrosine hydroxylase assay. The increase in tyrosinase activity was detectable by three assay methods: tyrosine hydroxylation, melanin synthesis, and by tyrosine decarboxylation. The formation of melanin, however, was found to be 1/20 that of either tyrosine hydroxylation or decarboxylation, a finding which suggests that the melanin pathway may be blocked at 5,6-dihydroxyindole. The “self-activation” response could not be mimicked by incubating cell homogenates with cyclic AMP-dependent protein kinase. Activated tyrosinase could be inhibited by the addition of fresh cell extracts, a finding which suggests that tyrosinase inhibitors may be present in these cells. This investigation was supported by Public Health Service grants CA41425 and CA30393 awarded by the National Cancer Institute, Bethesda, MD and by a research grant from the Proctor and Gamble Company.     

The effect of dexamethasone on transferrin secretion by cultured fetal rat hepatocytes

Cultured fetal rat hepatocytes derived from 12, 15 and 19-day gestation rats are capable of secreting transferrin. When dexamethasone is added to the medium an increased secretion rate is observed. The changes in secretion rates in control as well as dexamethasone-treated cells during culture have been shown to correlate with the level of mRNA coding for transferrin. Immunocytochemical experiments show that initially all hepatocytes contain transferrin which is localized in the lumina of the perinuclear space, rough endoplasmic reticulum and in the saccules and vesicles of the Golgi apparatus. During culture, particularly in control cells, the intensity of labelling varies from cell to cell. In addition, adjacent cells are observed to label more intensely in different intracellular organelles.     

The effects of lactate, acetate, glucose, insulin, starvation and alloxan-diabetes on protein synthesis in perfused rat hearts.

Compared with glucose, lactate + acetate stimulated ventricular protein synthesis in anterogradely perfused hearts from fed or 72 h-starved rats. Stimulation was greater on a percentage basis in starved rats. Atrial protein synthesis was not detectably stimulated by lactate + acetate. Insulin stimulated protein synthesis in atria and ventricles. The stimulation of protein synthesis by lactate + acetate and insulin was not additive, the percentage stimulation by insulin being less in the ventricles of lactate + acetate-perfused hearts than in glucose-perfused hearts. Perfusion of hearts from 72 h-starved or alloxan-diabetic rats with glucose + lactate + acetate + insulin did not increase protein-synthesis rates or efficiencies (protein synthesis expressed relative to total RNA) to values for fed rats, implying there is a decrease in translational activity in these hearts. In the perfused heart, inhibition of protein synthesis by starvation and its reversal by re-feeding followed a relatively prolonged time course. Synthesis was still decreasing after 3 days of starvation and did not return to normal until after 2 days of re-feeding.