Showing papers by "University of Sussex published in 1972"

Nitrogenase of Klebsiella pneumoniae. Purification and properties of the component proteins.

Abstract: 1. Nitrogenase from the facultative anaerobe Klebsiella pneumoniae was resolved into two protein components resembling those obtained from other nitrogen-fixing bacteria. 2. Both proteins were purified to homogeneity as shown by the criteria of disc electrophoresis and ultracentrifugal analysis. 3. The larger component had a mol.wt. of 218000 and contained one Mo atom, 17Fe atoms and 17 acid-labile sulphide groups/mol; it contained two types of subunit, present in equal amounts, of mol.wts. 50000 and 60000. All the common amino acids were present, with a predominance of acidic residues. The apparent partial specific volume was 0.73; ultracentrifugal analysis gave s020,w=11.0S and D020,w=4.94×10−7cm2/s. The specific activities (nmol of product formed/min per mg of protein) when assayed with the second nitrogenase component were 1500 for H2 evolution, 380 for N2 reduction, 1200 for acetylene reduction and 5400 for ATP hydrolysis. The reduced protein showed electron-paramagnetic-resonance signals at g=4.3, 3.7 and 2.015; the Mossbauer spectrum of the reduced protein consisted of at least three doublets. The u.v. spectra of the oxidized and reduced proteins were identical. On oxidation the absorbance increased generally throughout the visible region and a shoulder at 430nm appeared. The circular-dichroism spectra of both the oxidized and reduced proteins were the same, consisting mainly of a negative trough at 220nm. 4. The smaller component had mol.wt. 66800 and contained four Fe atoms and four acid-labile sulphide groups in a molecule comprising two subunits each of mol.wt. 34600. All common amino acids except tryptophan were present, with a predominance of acidic residues. The apparent partial specific volume calculated from the amino acid analysis was 0.732, which was significantly higher than that obtained from density measurements (0.69); ultracentrifugal analysis gave s020,w=4.8S and D020,w=5.55×10−7cm2/s. The specific activities (nmol of product formed/min per mg of protein) were 1050 for H2 evolution, 275 for N2 reduction, 980 for acetylene reduction and 4350 for ATP hydrolysis. The protein was not cold-labile. The reduced protein showed electron-paramagnetic-resonance signals in the g=1.94 region. The Mossbauer spectrum of the reduced protein consisted of a doublet at 77°K. The u.v. spectra of reduced and O2-inactivated proteins were identical, and inactivation by O2 generally increased the absorbance in the visible region and resulted in a shoulder at 460nm. The circular-dichroism spectra exhibited a negative trough at 220nm and inactivation by O2 decreased the depth of the trough. 5. The reduction of N2 and acetylene, and H2 evolution, were maximal at a 1:1 molar ratio of the Fe-containing protein to the Mo–Fe-containing protein; excess of the Mo–Fe-containing protein was inhibitory. All reductions were accompanied by H2 evolution. The combined proteins had no ATP-independent hydrogenase activity.

The chemical composition of Ricinus phloem exudate.

Abstract: The chemical composition of exudate obtained from incisions made in the bark of the stem of actively growing Ricinus plants has been determined. The exudate had a high dry matter content (100–125 mg/ml), a high sugar content (80–106 mg/ml) which was solely sucrose, reducing sugars being absent. The amino acid composition was mainly glutamic and aspartic acids and threonine with a total amino acid concentration of 35.2 mM. The exudate had a pH of 8.0–8.2. Potassium was the major cation (60–112 mM) with sodium present at a lower concentration (2–12 mM). Of the divalent cations, calcium was at a low concentration (0.5–2.3 mM) and magnesium relatively higher (4.5–5.4 mM). Chloride was the major inorganic anion (10–19 mM). Phosphate concentration was relatively high (3.7–5.7 mM) and low concentrations of sulphate (0.3–0.5 mM) and bicarbonate (1.7 mM) were also present. Nitrate was absent. The ionic balance was maintained by the presence of relatively large quantities (30–47 meq/l) of organic anions, mainly malate. Bioassays revealed auxin, gibberellin and cytokinin activities in chromatographed exudate. Adenosine triphosphate was found in the exudate (0.40–0.60 mM). The analysis is dicussed with respect to the composition of phloem sap reported for other plant species.

The effect of spatial arrangement on cell determination during mouse development

Abstract: The effect of cell position on cell determination was studied in mouse embryos. Embryos and parts of embryos were combined during early preimplantation development. The differentiation of cells in these composites was followed either by prelabelling some cells with tritiated thymidine or by combining cells which synthesized different electrophoretic variants of glucose phosphate isomerase. It was found that each blastomere of a 4-cell embryo could form both the trophoblast and the inner cell mass of the blastocyst. However, when blastomeres of a 4-cell embryo were placed on the outside of other 4-cell embryos then (a) they tended to form the outside layer of the blastocyst, (b) they tended to develop into the trophoblast and the yolk sac on the 10th day of pregnancy, (c) they tended not to form the coat colour of the foetus. Four- to eight-cell embryos which were completely surrounded by other blastomeres had lost the capacity to form vesicles at the blastocyst stage. We could find no evidence for the segregation of morphogenetic factors at the 4- and 8-cell stages of mouse development and concluded that at these stages cell position could determine the development of blastomeres.

Selective attention and performance in dangerous environments.

Abstract: Evidence on human performance in dangerous environments is reviewed and suggests that danger reduces efficiency, except in the case of experienced subjects. Perceptual narrowing is shown to be one source of decrement. It is suggested that danger increases the subject's arousal level which influences performance by producing a narrowing of attention. The nature of the performance decrement and of adaptation to danger are discussed in this context.

What are we trying to Measure

Abstract: Summary Development means creating the conditions for the realization of human personality. Its evaluation must therefore take into account three linked economic criteria: whether there has been a reduction in (i) poverty; (ii) unemployment; (iii) inequality. G.N.P. can grow rapidly without any improvement on these criteria; so development must be measured more directly. The conceptual and practical problems of a number of indicators are discussed and also the implications for planning, both national and international.

Genetic Transfer of Nitrogen Fixation from Klebsiella pneumoniae to Escherichia coli

Abstract: TRANSFER of nitrogen fixation genes (nif) within Klebsiella pneumoniae has been accomplished by transduction1 and conjugation2 These reports have all concerned intra-strain crosses: the transfer of nif to mutants of the same strain deficient in nitrogen fixation We now report the intergeneric transfer of nif from K pneumoniae to Escherichia coli, a species which does not naturally fix nitrogen

Salt Tolerance in Suaeda maritima (L.) Dum THE EFFECT OF SODIUM CHLORIDE ON GROWTH, RESPIRATION, AND SOLUBLE ENZYMES IN A COMPARATIVE STUDY WITH PISUM SATIVUM L

Abstract: The effect of sodium, chloride on the growth of a halophyte, Suaeda maritima (L.) Dum., was compared with its effect on Pisum sativum L. cv. Alaska under controlled environmental conditions. The salt stimulated the growth of Suaeda maximally at concentrations of 170 to 340 mM while the growth of Pisum was inhibited even by 100 mM. Both species accumulated ions in the tops and the maximum concentrations of Na+ and Cl− rose in Suaeda to 860 mM (based on the water content) and 730 mM and in Pisum to 170 mM and 300 mM respectively. Respiration in both species was inhibited as the NaCl level in the culture solution was raised. Four supernatant enzymes (malic dehydrogenase, glucose-6-phosphate dehydrogenase, peroxidase, and acid phosphatase) prepared from Pisum and from Suaeda (grown either in the absence of added NaCl or in the presence of 340 mM NaCl) were assayed in various levels of sodium chloride. The dehydrogenases were markedly inhibited by increasing salt concentrations while there was a smaller effect on the peroxidase and acid phosphatase. There was no difference in the effect of salt on the enzymes prepared from the two species although one is halophilic and the other halophobic.

The Corpus Allatum and Oogenesis in Rhodnius Prolixus (Stål.) II. The Effects of Starvation

Abstract: 1. In females which have been re-fed after various periods of fasting there is a delay in the resumption of ovarian growth which becomes greater with longer periods of starvation. 2. In females kept without food for 28 days before re-feeding, vitellogenesis is not resumed until 4 or 5 days after the meal, whereas the concentration of yolk antigen in the haemolymph returns to its normal level by the third day after the meal. 3. A period of starvation induces an accumulation of oocytes in the size range below that of activation until the fourth or fifth day after re-feeding, when the terminal oocytes pass rapidly through the critical size range and enter vitellogenesis. 4. The tropharia of starved females exhibit a remarkably reduced affinity for the protein stain Ponceau S, and enlarged trophocytes with their characteristic inclusions are absent during the first 6 days after re-feeding.

Testosterone, Search Behaviour and Persistence

Abstract: WE have found that testosterone markedly increases the persistence with which male chicks respond to a particular type of stimulus. The data reported here are from search tests, but the effect has now been confirmed in discrimination and open-field tests. Apparently similar effects of androgens on cognitive processes in men have recently been described1,2, so that it is possible that we are dealing with an effect which is present in both birds and mammals.

The Corpus Allatum and Oogenesis in Rhodnius Prolixus (Stål.) I. The Effects of Allatectomy

Abstract: 1. In the ovarioles of both normal and allatectomized females the spaces open between the cells of the follicle layer and vitellogenesis begins as the terminal oocyte grows through the 350-400 /µm size range. 2. In both normal and allatectomized ovarioles the growth of the larger oocytes is markedly co-ordinated so that, for example, each ovariole contains only one oocyte in active vitellogenesis. 3. A consideration of the size distribution of the terminal oocytes in normal and allatectomized ovarioles demonstrates that vitellogenesis begins later and proceeds more slowly in allatectomized animals. 4. Allatectomy markedly depresses the number of mitoses in the trophic primordium, but this is held to be a feedback phenomenon resulting from a decreased demand for the products of mature trophocytes. 5. There is a decreased level of yolk protein in the haemolymph of allatectomized animals. 6. This evidence favours the hypothesis that the primary site of action in Rhodnius of the gonadotropin from the corpus allatum is situated at the level of activation, whereby spaces open between the follicle cells and proteins from the haemolymph are allowed free access to the oocyte surface.

Post-replication repair of dna in ultraviolet-irradiated mammalian cells. No gaps in dna synthesized late after ultraviolet irradiation.

Abstract: Ultraviolet light produces pyrimidine dimers in cellular DNA. In mouse cell lines the great majority of these pyrimidine dimers are not excised, but remain in high molecular weight DNA. Hence the DNA used as template for DNA synthesis in the first generation after ultraviolet irradiation must contain such dimers. In two mouse cell lines (L5178Y and 3T3), alkaline sucrose sedimentation studies showed that the DNA pulse-labelled shortly after irradiation contained gaps, which by analogy with the situation in Escherichia coli, are presumed to be opposite the pyrimidine dimers. In contrast such gaps could not be detected in DNA pulse-labelled several hours after irradiation, despite the fact that dimers must have been present on the template strands. A possible explanation is that gaps were still being formed, but were filled in rapidly and were therefore not detected. This hypothesis was tested as follows. Either 1 or 8 h after ultraviolet irradiation cells were pulse-labelled in the presence of theophylline. This purine inhibits the filling in of gaps presumably by binding to the DNA in the gap. Even in the presence of theophylline, the late-synthesized DNA was considerably larger than the early-synthesized DNA. This suggests that at late times after irradiation, gaps were either not formed at all opposite the dimers, or were so transient that theophylline could not bind and inhibit their filling in. A model for synthesis of DNA on templates containing pyrimidine dimers in mammalian cells, based on these findings and other recent results, is discussed.

Interpretation of Recent Results on He 3 Below 3 mK: A New Liquid Phase?

Abstract: It is demonstrated that recent NMR results in $^{3}\mathrm{He}$ indicate that at 2.65 mK, the liquid makes a second-order transition to a phase in which the "spin-orbit" symmetry is spontaneously broken. The hypothesis that this phase is a BCS-type phase in which pairs form with $l$ odd, $S=1$, ${S}_{z}=\ifmmode\pm\else\textpm\fi{}1$ leads to reasonable agreement with both NMR and thermodynamic data, but involves some difficulties as to stability.

Chapter XIII The Acetylene Reduction Test for Nitrogen Fixation

Abstract: Publisher Summary This chapter discusses the acetylene reduction test for nitrogen fixation. The acetylene reduction test provides strong evidence for nitrogenase and is of considerable value both at the ecological level and in enzymology. With a good gas–liquid chromatograph, its sensitivity is about 1000 times that of traditional Kjeldahl analyses. This fact must be borne in mind when activities assessed by other methods are being compared with acetylene reduction. It is possible to obtain extracts or organisms with apparently high acetylene reducing activity but undetectable N2 fixation or 15N2 incorporation. Usually, a simple calculation of specific rates shows that these are experimental artefacts, but ATP-activated reduction of acetylene to ethylene might occur by mechanisms unrelated to nitrogen fixation. Critical experiments should, therefore, be checked by tests involving actual reaction with nitrogen and, where possible, tests involving repression of the system by ammonium ions.

The range of attraction of animal baits and carbon dioxide for mosquitoes. Studies in a freshwater area of West Africa

Abstract: In an inland area of the Gambia the density of flying mosquitoes at successive distances from a pair of bait-calves or an equivalent source of carbon dioxide was measured with ramp-traps to determine the maximum range at which orientation towards the bait was initiated. Thirty-six traps were operated at intervals of 7·5 m up to a distance of 60 m from the bait, on 66 nights. Anopheles ziemanni Grunb., Mansonia uniformis (Theo.) and Aedes spp. were responding to the presence of the baitcalves from a distance of 22·5–30 m; with carbon dioxide as bait the same species showed a clear response at 15 m but, with the doubtful exception of M. uniformis, not at 22·5–30 m. M. africana (Theo.) responded to both calf and carbon dioxide baits at 15 m but not at more distant ranges. Culex thalassius Theo. and C. univittatus Theo. showed a response at 7·5 m but not at any greater distance. C. decens group showed no response to either bait even in the nearest traps (7·5 m). The parous rate in Mansonia spp. varied with distance from the bait. Similar variation in the proportion of females infested with mites was not detected.

Vernier acuity as affected by target length and separation

Abstract: Vernier acuity was measured for vertical lines of different lengths; the threshold (about 4 sec of arc) was almost as good for the shortest stimuli (1 min 20 sec squares) as for the longest (21 min 20 sec × 1 min 20 sec rectangles) and did not change when two round dots were shown in positions corresponding to the squares. The threshold for the two dots measured in terms of minimum detectable lateral offset increased when the vertical separation between the dots increased, but, when replotted in terms of the angle of tilt between them with respect to vertical, the threshold improved with dot separation; moreover, at asymptote, the threshold was comparable to that obtained for detecting that an actual line was tilted out of vertical. Our data suggest that, in performing the vernier task, Ss do not extrapolate the edges of the vernier elements; instead, they judge the deviation of the inner ends of the stimuli from verticality. This hypothesis explains the effect of increasing separation between vernier elements and also accounts for other types of acuity, such as the detection of curvature.

The energy distribution of sputtered atoms from gold

Abstract: The energy spectra of atoms sputtered from a gold target have been measured as a function of ion energy and species for target temperatures in the range 100 to 1200°K. Both single crystal and polycrystal targets have been used, with surface topography monitored by a scanning electron microscope. The effect of raising the target temperature towards 1200°K is always to produce a low energy peak in the energy spectrum near 0.1 eV. This is found to have behaviour consistent with a thermal spike model, and at high temperature accounts for a large fraction of the total sputtering yield. The time-of-flight spectra show two peaks, one at about 10 eV the other at about 500 eV. The former was always present and when a crystal target was used with ejection along a axis it took on a kinked shape consistent with a contribution from focused collisions. The effect of increasing the temperature was to reduce this effect, presumably by thermal scattering of focused collisions. The 500 eV peak was also affec...