Showing papers by "Stockholm University published in 1993"

Crystal structure of a bacterial non-haem iron hydroxylase that catalyses the biological oxidation of methane

Abstract: The 2.2 A crystal structure of the 251K alpha 2 beta 2 gamma 2 dimeric hydroxylase protein of methane monooxygenase from Methylococcus capsulatus (Bath) reveals the geometry of the catalytic di-iron core. The two iron atoms are bridged by exogenous hydroxide and acetate ligands and further coordinated by four glutamate residues, two histidine residues and a water molecule. The dinuclear iron centre lies in a hydrophobic active-site cavity for binding methane. An extended canyon runs between alpha beta pairs, which have many long alpha-helices, for possible docking of the reductase and coupling proteins required for catalysis.

The structure of crystalline profilin-beta-actin.

Abstract: The three-dimensional structure of bovine profilin–β-actin has been solved to 2.55 A resolution by X-ray crystallography. There are several significant local changes in the structure of β-actin compared with α-actin as well as an overall 5° rotation between its two major domains. Actin molecules in the crystal are organized into ribbons through intermolecular contacts like those found in oligomeric protein assemblies. Profilin forms two extensive contacts with the actin ribbon, one of which appears to correspond to the solution contact in vitro.

Mechanisms of action on Escherichia coli of cecropin P1 and PR-39, two antibacterial peptides from pig intestine.

Abstract: Cecropin P1 and PR-39 are two antibacterial peptides isolated from the upper part of the small intestine of the pig. They have been sequenced, and their antibacterial spectra have been investigated (J.-Y. Lee, A. Boman, C. Sun, M. Andersson, H. Jornvall, V. Mutt, and H. G. Boman, Proc. Natl. Acad. Sci. USA 86:9159-9162, 1989; B. Agerberth, J.-Y. Lee, T. Bergman, M. Carlquist, H. G. Boman, V. Mutt, and H. Jornvall, Eur. J. Biochem. 202:849-854, 1991). We have now compared these two peptides for their mechanism of action on Escherichia coli K-12 by using three strains with different markers. Our results show that cecropin P1, like other cecropins, kills bacteria by lysis and that this reaction requires more peptide to kill more cells. PR-39 requires a lag period of about 8 min to penetrate the outer membrane of wild-type E. coli; then killing is quite fast. This lag period was absent in the envA1 mutant; in this strain the outer membrane was freely permeable to both peptides. PR-39 killed growing bacteria faster than nongrowing cells; for cecropin P1 there was no such difference. It is suggested from isotope incorporation experiments that PR-39 kills bacteria by a mechanism that stops protein and DNA synthesis and results in degradation of these components.

Dynamics of genets in clonal plants

Abstract: Processes related to dispersal, recruitment and survivorship of 'genetic individuals' in clonal plants have long been considered enigmatic. Little is known of whole life-cycle dynamics in these, usually, very long-lived plants. However, inferences may be drawn from studies of specific aspects of clonal plant populations, in particular seedling recruitment, genetic structure and growth form variation. This review summarizes recent findings from such studies, and presents some conclusions concerning genet population structure and regulation, and life history evolution in clonal plants.

Poverty, tnequaltty, and famtly living standards impacts across seven nations: the effect of noncash subsidies for health, education and housing

Abstract: The main aim of this paper has been to summarize the impact of noncash income–health and health education benefits, and imputed rent-on living standards, income distribution and poverty in seven nations at the beginning of the 1980s using the Luxembourg Income Study database. Our results do not give rise to a pattern of national differences in poverty rates or income inequality which are markedly different from that which emerges from previous LIS research based on cash income alone. While these results may be sensitive to the techniques used to measure and value noncash benefits in this paper, it appears that noncash income reinforces the redistributive impact or conventional (cash) tax-transfer mechanisms rather than acting to offset them in any major way.

Ubiquinol: an endogenous antioxidant in aerobic organisms.

Abstract: Ubiquinone (coenzyme Q), in addition to its function as an electron and proton carrier in mitochondrial and bacterial electron transport linked to ATP synthesis, acts in its reduced form (ubiquinol) as an antioxidant, preventing the initiation and/or propagation of lipid peroxidation in biological membranes and in serum low-density lipoprotein The antioxidant activity of ubiquinol is independent of the effect of vitamin E, which acts as a chain-breaking antioxidant inhibiting the propagation of lipid peroxidation In addition, ubiquinol can efficiently sustain the effect of vitamin E by regenerating the vitamin from the tocopheroxyl radical, which otherwise must rely on water-soluble agents such as ascorbate (vitamin C) Ubiquinol is the only known lipid-soluble antioxidant that animal cells can synthesize de novo, and for which there exist enzymic mechanisms that can regenerate the antioxidant from its oxidized form resulting from its inhibitory effect of lipid peroxidation These features, together with its high degree of hydrophobicity and its widespread occurrence in biological membranes and in low-density lipoprotein, suggest an important role of ubiquinol in cellular defense against oxidative damage Degenerative diseases and aging may bc1 manifestations of a decreased capacity to maintain adequate ubiquinol levels

Galanin--a neuroendocrine peptide.

Abstract: Galanin is a widely distributed 29/30 amino acid long neuropeptide with multiple biological effects. It inhibits glucose-induced insulin release, hippocampal acetylcholine release, hippocampal glutamate but not GABA release, and it lowers spinal excitability and firing of locus coeruleus neurons. It stimulates food (fat) intake and growth hormone release upon hypothalamic or i.c.v. injection. Galanin actions are mediated via high affinity Gi/G0 protein-coupled receptors--involving effector systems such as K(+)-, Ca(2+)-channels and adenylate cyclase. Galanin receptor agonists are thought to have therapeutic application in treatment of chronic pain and prevention of ischemic damage; galanin receptor antagonists have therapeutic potential in the treatment of Alzheimer's disease, depression, and feeding disorders.

European Exchange Rate Credibility Before the Fall

Abstract: Realignment expectations which measure exchange rate credibility are analyzed for European exchange rates, using daily financial data since the inception of the EMS. It is difficult to find economically meaningful relationships between realignment expectations and macroeconomic variables, although there are signs that lower inflation improves credibility. Statistically, many movements to realignment expectations are common to ERM participants. There were few indications of poor ERM credibility before late August 1992; the dimensions of the currency crisis of September 1992 appear to have taken both policy-makers and private agents largely by surprise.

European exchange rate credibility before the fall

Abstract: Realignment expectations which measure exchange rate credibility are analyzed for European exchange rates, using daily financial data since the inception of the EMS. It is difficult to find economically meaningful relationships between realignment expectations and macroeconomic variables, although there are signs that lower inflation improves credibility. Statistically, many movements to realignment expectations are common to ERM participants. There were few indications of poor ERM credibility before late August 1992; the dimensions of the currency crisis of September 1992 appear to have taken both policy-makers and private agents largely by surprise. kw]Realignment; Expectations; Currency crisis; ERM; EMS JEL classification: F31

Chlorinated and brominated persistent organic compounds in biological samples from the environment

Abstract: Eleven selected biological samples representing different ecosystems, trophic levels, and areas mainly in Sweden have been analyzed for 31 halogenated organic compounds or compound groups. The multiresidue analytical method provides a good opportunity to compare the concentrations of the different compounds in the investigated samples. By the use of ratios of these concentrations, comparisons can be done between species and areas. An attempt to describe an environmental distribution profile is demonstrated for some of the compounds using the concentration ratio between these compounds and 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153). Chlorinated paraffins (CPs) were found in all samples (130-4,400 ng/g lipid weight [lw]) and in some of them at higher concentrations than the polychlorinated biphenyls (PCBs). The ratio of CP to PCB 153 is higher in the investigated terrestrial species than in the aquatic, which is not the case for the other compounds. Polybrominated diphenyl ethers (PBDEs) were also found in all but one sample (< 3-2,140 ng/g lw). The concentrations were highest in industrialized areas but were also present in samples from background areas. Seven major congeners of PCBs were determined; the sum ranged from 50 to 200,000 ng/g lw in the investigated samples. Three coplanar PCB congeners were also analyzed (0.42-160 ng/g lw) as well as polychlorinated naphthalenes (PCNs), which were found at levels between 0.038 and 50 ng/g lw. The latter two groups do not seem to biomagnify in the food chain of herring to grey seal to the same extent as the major PCB compounds. Pentachlorobenzene was found in only three of the samples (0.6-35 ng/g lw), whereas hexachlorobenzene was present in all samples (9-330 ng/g lw). Among the organochlorine pesticides, total DDTs ranged from 4 to 280,000 ng/g lw and the hexachlorocyclohexanes (HCHs) from < 19 to 650. Chlordane (< 6-4,000 ng/g lw), toxaphene (not detected-5,700), and dieldrin (< 11-340) were also found. None of the analyzed polychlorinated phenols and guaiacols were detected in any of the investigated samples.

Polyandry and its effect on female reproduction in the green-veined white butterfly ( Pieris napi L.)

Abstract: In many insects nutrients transferred by the male to the female at mating are later incorporated into both the eggs and soma of the mated females. Accordingly, it has been suggested that female insects can use these male-derived nutrients both for somatic maintenance and to increase both the number and quality of their offspring. Moreover, much discussion is presently devoted to whether the male nuptial gift represents paternal investment, defined as “any increase in given male's total surviving progeny by increasing the reproductive output by a given female”, or mating effort which obtains “if a male gains by increasing the proportion of eggs he fertilizes from a given female” (Parker and Simmons 1989). If the male nuptial gift represents parental investment it should be expected to benefit predominantly the offspring sired by the donor, whereas the “physiological fate” of the male nuptial gift is somewhat irrelevant under the mating effort explanation. In this paper we test these issues by studying the lifetime fecundity, egg weights and longevity of two groups of females of the polyandrous green-veined white butterfly, Pieris napi, one group of which was allowed to mate only once and the other of which was allowed to mate at liberty, the latter group of females mating on average 2.28 times. Moreover, to test the incorporation rate of male-derived nutrients, we performed a second set of experiments where females were allowed to mate with radioactively labelled males. The results showed that polyandrous females had higher lifetime fecundity compared to monandrous females, laying on average 1.61 as many eggs, and that the difference in cumulative fecundity between the two groups was statistically significant from the 5th day of egg-laying onwards. Polyandrous females also lived longer and maintained egg weight at a high level for longer than monandrous females. Largely concomitant with egg-laying rate, incorporation rate of male-derived nutrients peaked 3–4 days after mating, subsequently tapering off to stabilize at about 40% of the maximum. Given the opportunity, female P. napi remated after 3–5 days, the duration of the refractory period being positively correlated with ejaculate mass. Hence, although the nutrient investment of the first male to mate with a female “subsidizes” the progeny of later-mating males, the male nuptial gift in P. napi clearly qualifies as both paternal investment and mating effort.

Public Policy as the Fuel of Fertility: Effects of a Policy Reform on the Pace of Childbearing in Sweden in the 1980s:

Abstract: In Sweden the total fertility rate (TFR) stopped declining in the late 1970s and started rising in the mid-1980s. The TFR exceeded the replacement level in 1990 and stayed above it in 1991. Characteristics of this recent fertility increase and the role of public policies are discussed. A technique called improved indirect standardization produced annual indexes of the level of childbearing at various birth orders. Swedish first-birth rates for single years of age for each calendar year from 1961 to 1990 were split into groups of ages. The rates al all ages below 30 generally fell from the mid-1960s through the early 1980s but there has been a mild recovery since 1984. At ages above 30 first-birth rates rose strongly in the 1980s as part of a steady postponement of the first birth to higher ages than before. About 82% of Swedish women who become mothers also had a second child and almost 40% of these also had a third child. Third-order birth rates increased up to the third year after the second birth and then declined steadily. The level of third and fourth birth rates fell from the mid-1960s to about 1977 and then recovered. The curves rose particularly strongly for mothers of children of age 1 with a further boost for this group starting about 1984. The strongly positive fertility gradient for age 1 of the youngest child and the corresponding break in 1986 for age 2 (but not age 2.5) may be a response to policy change. Recent fertility developments can be attributed to the muted pronatalism of social policies the growth of the day-care system and the extension of parental leave from 9 to 12 months. During the 1970s a premium on further childbearing was paid provided the interval between the 2 births did not exceed the period of statutory leave plus 6 months.

Selection of exaggerated male traits by female aesthetic senses

Abstract: DARWIN1 suggested that many apparently deleterious secondary sexual characters in males, such as bright colours, elaborate ornaments and conspicuous displays, evolved as a result of female choice Darwin never tried to explain the crucial agent of selection, that females have preferences for exaggerated male traits Rather, he took it for granted that females of many species possess a 'sense of the beautiful', akin to the aesthetic sense in humans The question of why such preferences evolve remains a controversial issue2,3 Here we report that mechanisms concerned with signal recognition possess inevitable biases in response that act as important agents of selection on signal form The existence of such biases may be sufficient to explain the evolution of exaggerated male secondary sexual traits, and elaborate signals in general

A comparison between actual distributions of annual and lifetime income: sweden 1951–89

Abstract: This paper uses register data on tax assessed income from 1951 to 1989 for a representative sample of Swedish men in order to compare the distributions of annual income and “lifetime” income. It is found that the dispersion of lifetime income is around 35 to 40 percent lower than typical cross-sections of annual income. It is income up to around 30 years of age that mainly explains this discrepancy in the magnitude of dispersions. From the age of 30 until 65 years the correlations between annual and lifetime income are quite high and the dispersion of annual income is not very much higher than the dispersion of lifetime income. An analysis of the evolution of income mobility shows that there is a slight tendency to rising mobility over time. This finding implies that the common approach to study the development of income distribution by using only annual income can be misleading.

Judgment and Decision Making Under Time Pressure

Abstract: The aim of the present chapter is to provide a review of empirical studies involving time pressure, judgment, and decision making, which have been published during the past three decades. The chapter will not cover theoretical approaches to decision making and judgment or biological aspects related to time pressure because these issues are well covered elsewhere in this volume (the chapters by Maule & Svenson; Lundberg; Maule & Hockey). Svenson (1990, 1991) suggests that higher level decision processes involve problem-solving processes, and therefore a few references including time pressure from that research area will also be cited as examples of relevant research.

Neuropeptides in the insect brain: a review.

Abstract: A major factor in the recognition of the diverse roles of neuropeptides in the nervous system was the development of radioimmunoassays and immunohistochemistry (see Guillemin 1978; H6kfelt et al. 1980; Krieger 1983). It became clear that not only neurosecretory cells, but also neurons use neuropeptides as messengers, and the impact of immunohistochemistry on our understanding of the chemical heterogeneity of neurons and the complexity of chemical signalling has been great. Since the late 1970s, when about 20 neuropeptides were known in mammals, considerable effort has been directed at why the central nervous system operates with so many neuropeptides, in addition to the fast neurotransmitters and the monoamines. Consequently, a large number of additional neuropeptides have been sequenced, and their distribution patterns, often colocalized with other neuroactive compounds, have been found to be extremely complex. Also, in the last 20 years much has been learned about the diverse roles of neuropeptides, especially how they regulate neurotransmission (Lehmann 1990; Krause etal. 1990; Cooper etal. 1991; H6kfelt 1991). Many important achievements in neuropeptide biology have been made with invertebrates as experimental animals. Invertebrates offer unique opportunities to study neuropeptides at the single cell level due to the presence of large identifiable neurons that are embedded in comparatively simple circuits or that have targets accessible for analysis of peptide action (Scheller et al.

Differential expression of the psbA genes in the cyanobacterium Synechocystis 6803.

Abstract: The 5′ region and transcription initiation sites of the psbA-2 and psbA-3 genes of Synechocystis 6803 were determined. The otherwise highly homologous genes were shown to diverge significantly in the 5′ noncoding regions. The transcription start site for the psbA-2 gene was mapped to position — 49 upstream of the coding region and for the psbA-3 gene to position — 88, i.e. 38 by upstream of the psbA-2 transcription start point. Both genes exhibit promoter elements, which conform in sequence and position to Escherichia coli consensus motifs. The two genes share identical — 35 sequences but differ in their — 10 sequences. Primer extension analysis demonstrated that the psbA-2 and psbA-3 genes are differentially expressed, with > 90 % of the total psbA transcripts being produced by the psbA-2 gene and the rest by the psbA-3 gene. Inactivation of the psbA-2 gene resulted in an eightfold up-regulation of the psbA-3 gene. The strikingly higher stability of the psbA transcripts in darkness compared to light, and the accumulation of a specific decay intermediate under dark conditions was reported previously. We show here that this dark-stability applies to both the psbA-2 and psbA-3 transcripts. The psbA-3 transcript did not appear to produce the processed intermediate, arguing for the involvement of the 5′ non-coding region as a determinant in psbA transcript degradation.