Showing papers by "University of Utah published in 1988"

Homologous plant and bacterial proteins chaperone oligomeric protein assembly

Abstract: An abundant chloroplast protein is implicated in the assembly of the oligomeric enzyme ribulose bisphosphate carboxylase-oxygenase, which catalyses photosynthetic CO2-fixation in higher plants. The product of the Escherichia coli groEL gene is essential for cell viability and is required for the assembly of bacteriophage capsids. Sequencing of the groEL gene and the complementary cDNA encoding the chloroplast protein has revealed that these proteins are evolutionary homologues which we term 'chaperonins'. Chaperonins comprise a class of molecular chaperones that are found in chloroplasts, mitochondria and prokaryotes. Assisted post-translational assembly of oligomeric protein structures is emerging as a general cellular phenomenon.

Models of dispersal in biological systems

Abstract: In order to provide a general framework within which the dispersal of cells or organisms can be studied, we introduce two stochastic processes that model the major modes of dispersal that are observed in nature. In the first type of movement, which we call the position jump or kangaroo process, the process comprises a sequence of alternating pauses and jumps. The duration of a pause is governed by a waiting time distribution, and the direction and distance traveled during a jump is fixed by the kernel of an integral operator that governs the spatial redistribution. Under certain assumptions concerning the existence of limits as the mean step size goes to zero and the frequency of stepping goes to infinity the process is governed by a diffusion equation, but other partial differential equations may result under different assumptions. The second major type of movement leads to what we call a velocity jump process. In this case the motion consists of a sequence of "runs" separated by reorientations, during which a new velocity is chosen. We show that under certain assumptions this process leads to a damped wave equation called the telegrapher's equation. We derive explicit expressions for the mean squared displacement and other experimentally observable quantities. Several generalizations, including the incorporation of a resting time between movements, are also studied. The available data on the motion of cells and other organisms is reviewed, and it is shown how the analysis of such data within the framework provided here can be carried out.

Dominant role of N-type Ca2+ channels in evoked release of norepinephrine from sympathetic neurons.

Abstract: Multiple types of calcium channels have been found in neurons, but uncertainty remains about which ones are involved in stimulus-secretion coupling Two types of calcium channels in rat sympathetic neurons were described, and their relative importance in controlling norepinephrine release was analyzed N-type and L-type calcium channels differed in voltage dependence, unitary barium conductance, and pharmacology Nitrendipine inhibited activity of L-type channels but not N-type channels Potassium-evoked norepinephrine release was markedly reduced by cadmium and the conesnail peptide toxin omega-Conus geographus toxin VIA, agents that block both N- and L-type channels, but was little affected by nitrendipine at concentrations that strongly reduce calcium influx, as measured by fura-2 Thus N-type calcium channels play a dominant role in the depolarization-evoked release of norepinephrine

Prevalence of Hemochromatosis among 11,065 Presumably Healthy Blood Donors

Abstract: There is evidence that iron loading and organ damage can be prevented in patients with hemochromatosis if prophylactic phlebotomy is employed early in the disease--findings emphasizing the importance of early detection before clinical signs occur. This study was designed to determine the efficacy of transferrin saturation as a screening tool for hemochromatosis and to assess the frequency of homozygosity for the HLA-linked hemochromatosis gene in a healthy population. We screened 11,065 presumably healthy blood donors (5840 men and 5225 women). Donors with transferrin saturations of 62 percent or more after an overnight fast were considered potential homozygotes and were asked to undergo liver biopsy and pedigree analysis. The frequency of values for transferrin saturation of 62 or higher in men was 0.008 and in women 0.003. Thirty-eight persons with values higher than 62 were studied in detail; 35 underwent liver biopsy. Liver iron stores ranged from normal to markedly increased. Twelve siblings with an identical HLA match to a proband underwent liver biopsy, and 11 had increased liver iron stores. According to likelihood analysis of the pedigrees, 26 of the 38 probands were homozygotes, and 12 were heterozygotes. The estimated frequency of homozygosity was based on the data in men, because the threshold value of 62 for the transferrin saturation identified only half as many female homozygotes as expected. The frequency of homozygosity was 0.0045, corresponding to a gene frequency of 0.067. The value of population screening is demonstrated in these studies by the detection of homozygotes before clinical manifestations of hemochromatosis occur.

Effects of plant growth rate and leaf lifetime on the amount and type of anti-herbivore defense

Abstract: Growth, herbivory and defenses were studied for 41 common tree species in a lowland rainforest in Panama. Species represented a range of shade tolerance, but all individuals were measured in light gaps to control for environmental conditions and the availability of herbivores. Species growth rates and leaf lifetimes differed by almost 50-fold and were related to the degree of shade tolerance. Various measures of plant growth were significantly negatively correlated with an estimate of defense investment, and significantly positively correlated with rates of herbivory. Species with long-lived leaves had significantly higher concentrations of immobile defenses such as tannins and lignins. These data support current hypotheses that the intrinsic growth rate of a species evolutionarily determines the optimal amount and type of defense.

Does Biology Constrain Culture

Abstract: Most social scientists would agree that the capacity for human culture was probably fashioned by natural selection, but they disagree about the implications of this supposition. Some believe that natural selection imposes important constraints on the ways in which culture can vary, while others believe that any such constraints must be negligible. This paper employs a “thought experiment” to demonstrate that neither of these positions can be justified by appeal to general properties of culture or of evolution. Natural selection can produce mechanisms of cultural transmission that are neither adaptive nor consistent with the predictions of acultural evolutionary models (those ignoring cultural evolution). On the other hand, natural selection can also produce mechanisms of cultural transmission that are highly consistent with acultural models. Thus, neither side of the sociobiology debate is justified in dismissing the arguments of the other. Natural selection may impose significant constraints on some human behaviors, but negligible constraints on others. Models of simultaneous genetic/cultural evolution will be useful in identifying domains in which acultural evolutionary models are, and are not, likely to be useful.

Interferon-γ and tumor necrosis factor induce the L-arginine-dependent cytotoxic effector mechanism in murine macrophages*

Abstract: We tested several monokines and muramyl dipeptide (MDP) to determine whether they induce the L-arginine-dependent effector mechanism in cultured murine macrophages. Recombinant interferon-gamma (rIFN-gamma) and recombinant tumor necrosis factor (rTNF) synergize to induce nitrite (NO2-) and nitrate (NO3-) synthesis from L-arginine as well as to cause inhibition of the iron-dependent enzyme aconitase in macrophages. Unlike rTNF, recombinant interleukin 1 (rIL 1) and rIL 6/B cell stimulatory factor 2 (rIL 6/BSF-2) did not act as cofactors when added to macrophages in the presence of rIFN-gamma. rIFN-gamma plus MDP induced the L-arginine-dependent effector mechanism in murine macrophages. However, induction by rIFN-gamma plus MDP was inhibited by anti-rTNF antibodies which suppressed both NO2-/NO3- synthesis and aconitase inhibition. This result indicates that endogenously produced TNF is involved in the induction of the L-arginine-dependent effector mechanism when MDP is the co-stimulant with rIFN-gamma. In contrast, anti-rTNF antibodies did not fully suppress the effect of combining rIFN-gamma and lipopolysaccharide, suggesting that, in this case, activation of the L-arginine-dependent effector pathway may involve more than induction of TNF synthesis by the macrophages. These results provide information, at a biochemical level, on a mechanism through which combination of IFN-gamma and TNF can modulate macrophage functions involved in the control of cell proliferation.

Correlations between carbon isotope ratio and microhabitat in desert plants.

Abstract: Water is usually considered to be the key limiting factor for growth of desert plants, yet there is little information available of the water-use efficiency of species within a desert community. Leaf carbon isotope ratios, an indicator of long-term intercellular carbon dioxide concentrations and thus of water-use efficiency in C3 plants, were measured on species occurring within a Sonoran Desert community, consisting of wash, transition and slope microhabitats. Along a soil moisture gradient from the relatively wetter wash to the relatively drier slope, leaf carbon isotope ratios increased in all species, indicating that water-use efficiency increased as soil water availability decreased. Leaf carbon isotope ratios of long-lived perennials were substantially more positive than in short-lived perennials, even though plants were growing adjacent to each other. Leaf carbon isotope ratio and leaf duration (evergreen versus deciduous) were not correlated with each other. The results are discussed in terms of how the efficiency of water use may affect community structure and composition.

Hydrogen peroxide stimulates the synthesis of platelet-activating factor by endothelium and induces endothelial cell-dependent neutrophil adhesion.

Abstract: Oxidant-induced damage to the intima of pulmonary and systemic vessels is thought to be an important mechanism of injury in a variety of syndromes of vascular damage. Hydrogen peroxide (H2O2) is an active oxygen metabolite that may induce intimal injury by cytolytic attack or by inducing biochemical and functional alterations in the endothelial cells (EC); however, mechanisms involved in noncytolytic perturbation of EC are largely unknown. We found that H2O2 stimulated the synthesis of platelet-activating factor (PAF) by primary cultures of bovine pulmonary artery endothelium (BPAEC) and by human umbilical vein endothelium (HUVEC). In each cell type the incorporation of [3H]acetate into [3H-acetyl]PAF was concentration- and time-dependent and was temporally dissociated from severe plasma membrane disruption and cytolytic cell injury; the newly synthesized PAF remained associated with the EC. H2O2 caused permeabilization of EC to 45Ca2+ and an increase in intracellular Ca2+, suggesting that a transmembrane Ca2+ flux is the signal that initiates PAF synthesis. H2O2 also induced the endothelial cell-dependent adhesion of neutrophils to HUVEC monolayers. This response was rapid, with an onset within minutes and a subsequent time course that paralleled the time course of PAF accumulation, and was dependent on extracellular Ca2+ but not on de novo protein synthesis. These studies demonstrate that H2O2 can induce two rapid activation responses of endothelium, PAF synthesis and EC-dependent neutrophil adhesion, events that may be important in physiologic and pathologic inflammation.

Common inheritance of susceptibility to colonic adenomatous polyps and associated colorectal cancers.

Abstract: We studied 670 persons in 34 kindreds by flexible proctosigmoidoscopic examination (60 cm) to determine how frequently colorectal adenomas and cancers result from an inherited susceptibility. Kindreds were selected through either a single person with an adenomatous polyp or a cluster of relatives with colonic cancer. The kindreds all had common colorectal cancers, not the rare inherited conditions familial polyposis coli and nonpolyposis inherited colorectal cancer. Likelihood analysis strongly supported the dominant inheritance of a susceptibility to colorectal adenomas and cancers, with a gene frequency of 19 percent. According to the most likely genetic model, adenomatous polyps and colorectal cancers occur only in genetically susceptible persons; however, the 95 percent confidence interval for this proportion was 53 to 100 percent. These results suggest that an inherited susceptibility to colonic adenomatous polyps and colorectal cancer is common and that it is responsible for the majority of colonic neoplasms observed clinically. The results also reinforce suggestions that first-degree relatives of patients with colorectal cancer should be screened for colonic tumors. This evidence of an inherited susceptibility to a cancer with well-recognized environmental risk factors supports the hypothesis that genetic and environmental factors interact in the formation and transformation of polyps.

Oral zinc in macular degeneration.

Abstract: Macular degeneration associated with age and drusen, an important cause of severe visual loss in older persons, is of unknown cause. The sensory retina and retinal pigment epithelium, which are cell layers in zinc, appear to be prominently involved in the disease process. Because zinc plays a role in the metabolic function of several important enzymes in the chorioretinal complex, we undertook a prospective, randomized, double-masked, placebo-controlled investigation of the effects of oral zinc administration on the visual acuity outcome in 151 subjects with drusen or macular degeneration. Although some eyes in the zinc-treated group lost vision, this group had significantly less visual loss than the placebo group after a follow-up of 12 to 24 months. This is the first controlled oral intervention study to show a positive, if limited, treatment effect in macular degeneration, a major public health problem. Because of the pilot nature of the study and the possible toxic effects and complications of oral zinc administration, widespread use of zinc in macular degeneration is not now warranted.

Familial dyslipidemic hypertension. Evidence from 58 Utah families for a syndrome present in approximately 12% of patients with essential hypertension.

Abstract: Population-based sibships with essential hypertension diagnosed before the age of 60 years are being screened in Utah to find two or more hypertensive siblings with the same biochemical abnormality as a clue to an inherited cause for their specific type of hypertension. Among 131 hypertensive subjects in 58 sibships, concordant abnormalities in fasting serum lipid concentrations were observed in two or more siblings in 48% of the sibships. After adjusting for effects of antihypertensive medications, abnormal values reported in only 10% of the Lipid Research Clinics data were observed in 30% of patients for serum triglycerides, 19% for serum low-density lipoprotein cholesterol, and 39% for high-density lipoprotein cholesterol. More than one lipid level was abnormal in almost all concordant sibships, suggesting an association between hypertension and a syndrome of mixed lipid abnormalities, probably familial combined hyperlipidemia (renamed "familial combined dyslipidemia" because of common low high-density lipoprotein cholesterol levels). We conclude that familial dyslipidemic hypertension may be a specific syndrome with lipid abnormalities more severe than blood pressure elevations.

Sharp effective Nullstellensatz

Abstract: The usual proofs of this result, however, give no information about the g1's; for instance they give no bound on their degrees. This question was first considered by G. Hermann [H]. She used elimination theory to get a bound on the degree of the gi's which was doubly exponential in the number of variables. Her results were later improved in [MW] and in [Th]. All these produce bounds that are doubly exponential in the number of variables. A major breakthrough was achieved by Brownawell [B1] who proved the following result:

Sequence analysis and regulation of the htrA gene of Escherichin coli: a σ32-independent mechanism of heat-inducible transcription

Abstract: Previous work has established that the E. coli htrA gene product is essential for bacterial survival at temperatures above 42 degrees. We have sequenced the htrA gene region and found an open reading frame (ORF) coding for a protein of 491 amino acids with a calculated molecular weight of 51,163 daltons. This molecular weight corresponds well with that seen following electrophoresis on SDS-polyacrylamide gels. This protein has an amino-terminal sequence typical for a leader peptide and undergoes post-translational modification by cleavage of an amino-terminal portion. The insertional mutations which affect the function of the htrA gene map inside this ORF. The levels of htrA mRNA increase rapidly and transiently upon heat shock in a manner independent of the rpoH gene, which encodes the sigma 32 RNA polymerase subunit and is known to regulate transcription of typical heat shock genes. Using S1 mapping and RNA primer extension, we have identified the htrA promoter and found that it is similar to the P3 promoter of the rpoH gene. The P3 promoter is especially active at high temperatures and is recognized by a recently identified transcriptional factor, sigma E.

Heating rates in tropical anvils

Abstract: The interaction of infrared and solar radiation with tropical cirrus anvils is addressed. Optical properties of the anvils are inferred from satellite observations and from high-altitude aircraft measurements. An infrared multiple-scattering model is used to compute heating rates in tropical anvils. Layer-average heating rates in 2 km thick anvils were found to be on the order of 20 to 30 K/day. The difference between heating rates at cloud bottom and cloud top ranges from 30 to 200 K/day, leading to convective instability in the anvil. The calculations are most sensitive to the assumed ice water content, but also are affected by the vertical distribution of ice water content and by the anvil thickness. Solar heating in anvils is shown to be less important than infrared heating but not negligible. The dynamical implications of the computed heating rates are also explored and it is concluded that the heating may have important consequences for upward mass transport in the tropics. The potential impact of tropical cirrus on the tropical energy balance and cloud forcing are discussed.

Control Mechanisms in dsDNA Bacteriophage Assembly

Abstract: The introduction of the use of T-even bacteriophages as genetic and biochemical experimental systems by Max Delbruck in the late 1930s has led to the intense study of many aspects of bacteriophage biology. Of these, two related endeavors, the study of the structure and the assembly of the virions, have been very important models in the development of our current understanding of macromolecular assembly processes. Twenty years ago, Edgar, Kellenberger, Epstein, and collaborators nucleated these studies by showing that phage assembly follows defined pathways that can accumulate assembly intermediates when blocked and that the assembly-naive components of phage T4 thus accumulated could join properly in vitro (Epstein et al., 1963; Edgar and Wood, 1966; Wood et al., 1968). Since that time, the structure and assembly of many bacteriophages and other viruses have been studied. The possibility of completely defining the genetic systems, and therefore the proteins involved, has made phage assembly a particularly popular and tractable area in which to study macromolecular assembly. We will not consider it the mission of this chapter to collect the details of this myriad of studies. The reader should consult other chapters in this volume or other reviews for such details (e.g., Casjens and King, 1975; Murialdo and Becker, 1978a; Eiserling, 1979; Wood and King, 1979; King, 1980; DuBow, 1981; Mathews et al., 1983; Hendrix et al., 1983; Casjens, 1985c; Carrascosa, 1986). Instead we will focus on general questions currently under study and attempts to answer them in the various dsDNA phage systems. We will not discuss the problem of DNA packaging in detail and will not cover the lipid-containing dsDNA phages.

Characteristic trace-fossil associations in oxygen-poor sedimentary environments

Abstract: The sedimentologic record of oxygen-poor depositional environments typically includes trace fossils produced by deposit-feeding organisms. We propose an oxygen-controlled trace-fossil model in which increasing oxygen concentration of interstitial water in sediment parallels a transition from fodinichnia-dominated through pascichnia-dominated to domichnia-dominated trace-fossil associations. In certain places, such as parts of the late Paleozoic Oquirrh Basin in Utah, this model provides a reasonable alternative to the more traditional, depth-controlled model of trace-fossil distribution.

Specificity of the thiobarbituric acid reaction: its use in studies of lipid peroxidation.

Abstract: The thiobarbituric acid (TBA) reaction, quantified by colorimetry or fluorimetry, is the method most widely used for studying lipid peroxidation in both laboratory animals and in humans with disorders. However, concerns regarding its analytical specificity have often been expressed, because TBA reacts with a wide variety of chemical species to produce a pink to red color. In this study, we reacted TBA with various saturated and unsaturated aldehydes (both directly and in the presence of sucrose, fructose, and glucose), substituted pyrimidines, 2-deoxyribose, and N-acetylneuraminic acid. We also studied the TBA reaction with bilirubin, biliverdin, icteric serum, and serum containing hemolyzed erythrocytes, comparing the absorption spectra of these reaction products with that for malondialdehyde (MDA). The reaction products were also analyzed for MDA by high-performance liquid chromatography (HPLC). Although the TBA reaction with some of these compounds may not be important in biological studies, others could lead to misinterpretations of increased lipid peroxidation. Use of HPLC to quantify MDA is recommended because of its high analytical sensitivity and specificity, especially in the study of lipid peroxidation in human subjects.

Anomalous binding of epidermal growth factor to A431 cells is due to the effect of high receptor densities and a saturable endocytic system.

Abstract: This study was conducted to determine how extraordinarily high numbers of epidermal growth factor receptors (EGF-R) affected the binding and internalization of EGF in the transformed cell line A431. I found that at low EGF concentrations, the kinetics of binding behaved as a nonsaturable, first-order process showing no evidence of multiple-affinity classes of receptors. However, EGF dissociation rates were strongly dependent on the degree of receptor occupancy in both intact cells and isolated membranes. This occupancy-dependent dissociation appears to be due to diffusion-limited binding. EGF-induced receptor internalization was rapid and first order when the absolute number of occupied receptors was below 4 x 10(3) min-1. However, at higher occupancies the specific internalization rate progressively declined to a final limiting value of 20% normal. The saturation of EGF-R endocytosis was specific since internalization of transferrin receptors was not affected by high concentrations of either transferrin or EGF. Saturation of EGF-R endocytosis probably involves a specific component of the endocytic pathway since fluid phase endocytosis increased coordinately with EGF-R occupancy. I conclude that there are several aspects of EGF-R dynamics on A431 cells are neither similar to the behavior of EGF-R in other cell types nor similar to the reported behavior of other hormone receptors. Although A431 cells have an extraordinary number of EGF-R, they do not seem to have corresponding levels of at least two other crucial cell surface components: one that mediates EGF-induced rapid receptor internalization and one that attenuates EGF-induced membrane responses. These factors, in addition to the presence of diffusion-limited binding at low EGF concentrations, are probably responsible for the appearance of multiple-affinity classes of receptors in this cell type.

Bacterial motility: membrane topology of the Escherichia coli MotB protein.

Abstract: The MotB protein of Escherichia coli is an essential component of the force generators that couple proton movement across the cytoplasmic membrane to rotation of the flagellar motors. The membrane topology of MotB was examined to explore the possibility that it might form a proton channel. MotB--alkaline phosphatase fusion proteins were constructed to identify likely periplasmic domains of the MotB molecule. Fusions distal to a putative membrane-spanning segment near the amino terminus of MotB exhibited alkaline phosphatase activity, indicating that an extensive carboxyl-terminal portion of MotB may be located on the periplasmic side of the membrane. Protease treatment of MotB in spheroplasts confirmed this view. The simple transmembrane organization of MotB is difficult to reconcile with a role as a proton conductor.

Heparin immobilization onto segmented polyurethaneurea surfaces - Effect of hydrophilic spacers

Abstract: Heparin was immobilized onto segmented polyurethane-urea surfaces (Biomer) using hydrophilic poly(ethylene oxide) spacers of different chain lengths. The use of the hydrophilic spacer, poly(ethylene oxide), reduces protein adsorption and subsequent platelet adhesion on the surface. In addition, the bioactivity of the immobilized heparin is enhanced by the incorporation of these spacers. Immobilized heparin bioactivity is shown to be a function of PEO spacer length. Use of hydrophilic PEO spacers demonstrates that immobilized heparin's bioactivity is consistently higher than that of the C6 alkyl spacer, but heparin-immobilized surfaces demonstrate no chain length effect on platelet adhesion, even though they show less platelet adhesion compared to Biomer controls. In the case of PEO-grafted surfaces, platelet adhesion is decreased compared to Biomer controls, and C6 alkyl spacer-grafted surfaces, and exhibits a minimum at PEO 1000. In ex vivo A-A shunt experiments under low flow and low shear conditions, all heparinized surfaces exhibit significant prolongation of occlusion times compared to Biomer controls, indicating an ability of immobilized heparin to inhibit thrombosis in whole blood.

Reading frame switch caused by base-pair formation between the 3' end of 16S rRNA and the mRNA during elongation of protein synthesis in Escherichia coli.

Abstract: Watson-Crick base pairing is shown to occur between the mRNA and nucleotides near the 3' end of 16S rRNA during the elongation phase of protein synthesis in Escherichia coli. This base-pairing is similar to the mRNA-rRNA interaction formed during initiation of protein synthesis between the Shine and Dalgarno (S-D) nucleotides of ribosome binding sites and their complements in the 1540-1535 region of 16S rRNA. mRNA-rRNA hybrid formation during elongation had been postulated to explain the dependence of an efficient ribosomal frameshift on S-D nucleotides precisely spaced 5' on the mRNA from the frameshift site. Here we show that disruption of the postulated base pairs by single nucleotide substitutions, either in the S-D sequence required for shifting or in nucleotide 1538 of 16S rRNA, decrease the amount of shifting, and that this defect is corrected by restoring complementary base pairing. This result implies that the 3' end of 16S rRNA scans the mRNA very close to the decoding sites during elongation.