Showing papers by "University of Leicester published in 1974"
263 citations
TL;DR: Measurements of ingested ration, assimilated ration and metabolic rate in Mytilus edulis L. of different sizes have been integrated to provide an estimate of energy balance, which in turn describes the physiological state of the animal, allowing the empirical determination of growth efficiency and ration.
Abstract: Measurements of ingested ration, assimilated ration and metabolic rate in Mytilus edulis L. of different sizes have been integrated to provide an estimate of energy balance, which in turn describes the physiological state of the animal. These data allow the empirical determination of growth efficiency and ration. Growth efficiency increases hyperbolically with increasing ingested ration to reach a maximum, after which efficiency decreases as ration is further increased. The optimum ration for efficient growth increases with increasing weight of the mussel; maximum growth efficiency decreases with increasing body weight.
242 citations
TL;DR: In this paper, a study of the failure times of structural components which operate at temperatures sufficiently high to cause material deterioration due to creep rupture is made, and expressions are derived which give lower bounds on failure times and which take into consideration the different stress criteria known to affect rupture mechanisms.
Abstract: A study is made of the failure times of structural components which operate at temperatures sufficiently high to cause material deterioration due to creep rupture. Expressions are derived which give lower bounds on failure times and which take into consideration the different stress criteria known to affect rupture mechanisms. The formulae are used to predict failure times of a variety of components, and it is found convenient, from a practical point of view, to express the times in terms of an equivalent representative rupture stress. By using this stress, failure times are obtained directly from uniaxial stress rupture data. It is found in the examples studied that the values for the representative rupture stress are almost independent of the constants used to define the deformation and rupture processes. Experimental evidence supports the prediction of the theory; for example, copper bars in torsion show better rupture characteristics than bars of aluminium alloy. The position is reversed in notched tensile specimens, with the aluminium specimens showing better characteristics than those of copper. It can be deduced that it is the form of rupture mechanism which affects behaviour rather than ductility as might be expected, since the creep ductility of the aluminium alloy is much less than that for copper.
226 citations
155 citations
TL;DR: The New Mexican species was exceptional in showing little homology with other species with respect to either repetitive or slowly reassociating sequences, but higher levels of homology were observed in the case of repetitive sequences.
Abstract: Chromosomes and DNA sequence homologies have been studied in 15 species of North American salamander belonging to the genus Plethodon. These include 4 Eastern small species, 5 Eastern large species, 5 Western, and 1 New Mexican species. All species have 14 metacentric or sub-metacentric chromosomes. Their karyotypes are closely similar, but their C values range from 18–69 pg. DNA:DNA molecular hybridization studies showed that salamanders belonging to the same species group had between 60 and 90% of the observed repetitive DNA sequences in common, different groups of Eastern species had between 40 and 60% in common, and Eastern and Western groups had less than 10% in common. The slowly reassociating DNA sequences were also diverse among species, but higher levels of homology were observed than in the case of repetitive sequences. The New Mexican species was exceptional in showing little homology with other species with respect to either repetitive or slowly reassociating sequences.
147 citations
136 citations
Book•
01 Jan 1974129 citations
TL;DR: The digestive gland of My tilus edulis may also have a storage function and may therefore be involved in the utilisation of reserves during starvation and with changes induced by starvation and temperature stress.
Abstract: During recent years attention has been focused on the morphology of the bivalve digestive gland (Sumner, 1966a, b; Owen, 1970; Pal, 1971,1972) but there is little information concerning its role in the storage of energy reserves. Reid (1969) has suggested that in the horse clam, Tresus capax, digestive gland lipid may serve as an energy store which is depleted when food is scarce. Sastry (1966) and Sastry and Blake (1971) have shown that material stored in the digestive tissue of Aequipecten irradians is transferred to the gonad during gametogenesis and Vassallo (1973) has confirmed the transfer of lipid in Chlamys hericia. The digestive gland of My tilus edulis may also have a storage function and may therefore be involved in the utilisation of reserves during starvation. The present paper deals with seasonal changes in the biochemical composition of the digestive gland of M. edulis, and with changes induced by starvation and temperature stress.
125 citations
TL;DR: One of the axioms of ecology is that the diversity of species is greater at low than at high latitudes as discussed by the authors, which has been repeatedly demonstrated in the more conspicuous groups of organisms such as trees, birds, and butterflies.
Abstract: ONE of the axioms of ecology is that the diversity of species is greater at low than at high latitudes. This was appreciated by Alfred Russell Wallace more than a century ago and has been repeatedly demonstrated in the more conspicuous groups of organisms such as trees, birds, and butterflies. Ecologists have produced a variety of theories, none entirely satisfactory, to explain latitudinal gradients in diversity, but an understanding of the phenomenon remains as elusive today as in Wallace's time.
121 citations
TL;DR: The considerable progress which has been made in the last ten years in elucidating the rules governing the form and composition of cells of Escherichia coli as a function of growth rate and transit time is outlined in the Review.
Abstract: The size, shape and composition of cells in cultures of bacteria maintained in steady states of exponential growth depend on the cultural conditions employed. Important factors influencing these parameters are the growth rate of the culture and the transit time of replication forks from one end of a chromosome to the other. The considerable progress which has been made in the last ten years in elucidating the rules governing the form and composition of cells of Escherichia coli as a function of growth rate and transit time is outlined in the Review.
105 citations
TL;DR: Analysis of 500,000 C. nemoralis snails from throughout Europe shows that there is a strong positive association between gene frequencies at the shell color locus and mean summer temperature, but that no climatic correlations are obvious at other loci.
Abstract: Polymorphic snails of the genus Cepaea have been widely used for research in ecological genetics. Natural selection by selective predation is important in controlling morph frequencies in some populations of C. nemoralis in England. The importance of environmental selection in affecting other patterns of local genetic differentiation of population structure (area effects) is a matter of controversy. Some authors emphasize divergent evolution of whole gene pools between area effects, while others feel that climatic selection acting on individual loci is important. Analysis of 500,000 C. nemoralis snails from throughout Europe shows that there is a strong positive association between gene frequencies at the shell color locus and mean summer temperature, but that no climatic correlations are obvious at other loci. Another species, C. vindobonensis, which has a much simpler system of polymorphism than does C. nemoralis, was investigated in Yugoslavia, in a region where there is known to be intense microclimatic differentiation because of the accumulation of cold air in frost hollows. There was a striking tendency for snails with lightly pigmented shell bands to be found in places with a warm microclimate. Physiological and behavioral experiments demonstrate that this is due primarily to differential energy absorption from sunshine by the different shell phenotypes. As in C. nemoralis, other C. vindobonensis phenotypes show no detectable association with the environment. It is possible that genes whose frequencies cannot be related to environmental selection may have evolved strong linkage interactions with other genes in the population's gene pool. Selection by the ecological environment and the genetic environment may therefore both be important in controlling the genetic structure of snail populations.
TL;DR: Genetic evidence is presented which indicates that the Colonia strain CL, when crossed with heterothallic strains, also yields recombinant progeny and thus undergoes nuclear fusion and meiosis.
Abstract: The Colonia isolate of Physarum polycephalum produces plasmodia within amoebal clones. Wheals demonstrated genetically that amoebae of the C50 strain of this isolate, when crossed with heterothallic amoebae, yielded recombinant progeny. He concluded that nuclear fusion and meiosis occurred in these crosses and suggested that nuclear fusion was also involved in plasmodia formation in clones. He thus designated the strain ‘homothallic’.In the present work genetic evidence is presented which indicates that the Colonia strain CL, when crossed with heterothallic strains, also yields recombinant progeny and thus undergoes nuclear fusion and meiosis. Microdensitometric measurements of nuclear DNA content are reported which indicate that CL amoebae are haploid like heterothallic amoebae, and crossed plasmodia are diploid. However, clonally formed CL plasmodia were found to have the same G2 nuclear DNA content as CL amoebae. This observation excludes the possibility of nuclear fusion when plasmodia form within clones of CL amoebae and therefore the strain cannot be homothallic. Two alternatives, apogamy and coalescence, are proposed as the most likely mechanisms for clonal plasmodium formation in strain CL.
TL;DR: A review of the role of surface topography in tribology can be found in this article, where the most radical change which has occurred is the recent widespread acceptance of the concept that a typical tribological system can involve both elastic and plastic deformation of asperities.
TL;DR: In this article, the relative stabilities of phosphoranes are discussed in terms of the relative apicophilicities of groups, steric factors and ring strain, and experiments are described which give quantitative data on these.
Abstract: Five-coordinate phosphoranes are intermediates in substitution reactions at phosphorus. The relative stabilities of phosphoranes are discussed in terms of the relative apicophilicities of groups, steric factors and ring strain, and experiments are described which give quantitative data on these. The application of the results to discussion of the course of substitutions at phosphorus is briefly described.
TL;DR: Determination of the constitution and behavior of this organism's branched respiratory chain has contributed to the understanding of how respiration controls nitrogen fixation, and it is reasonable to assume that nitrogen fixation is an anaerobic process catalyzed by oxygen-sensitive proteins.
Abstract: Publisher Summary The chapter focuses on the work done toward this aspect; toward understanding how respiration and nitrogen fixation can function simultaneously in Azotobacter. Accordingly, only those aspects of this subject that are connected with the physiology of nitrogen fixation in aerobes will be discussed. In particular, determination of the constitution and behavior of this organism's branched respiratory chain has contributed to the understanding of how respiration controls nitrogen fixation. All nitrogenases from both aerobic and anaerobic organisms comprise two non-haem iron proteins, which have the same requirements for enzymic activity in vitro— namely, an anaerobic environment, a source of ATP, and a reluctant. The two component proteins that make up the nitrogenase enzyme complement each other in cross reactions between nitrogenase fractions from aerobic and some anaerobic sources and physiological electron carriers from one class of bacteria can donate electrons to nitrogenase from the other. The absence of oxygen is mandatory in nearly all measurements of nitrogen fixation in vitro. Crude preparations that show nitrogenase activity in the presence of oxygen have been obtained from aerobic nitrogen fixers. From the foregoing evidence it is reasonable to assume that nitrogen fixation is an anaerobic process catalyzed by oxygen-sensitive proteins. How these operate and survive in an aerobic bacterium is discussed in detail. Because oxygen uptake is the major electron-utilizing metabolic process in Azotobacter, the respiratory chain involving electron transport and oxidative phosphorylation are described.
TL;DR: It is concluded that during development there is a requirement for the destruction of specific RNA and protein molecules for reasons other than the provision of oxidizable substrates.
Abstract: 1. Methods of obtaining myxamoebae of Dictyostelium discoideum strain Ax-2 (ATCC 24397) with glycogen contents in the range 0.05-5mg of glycogen/10(8) cells are described. The changes in cellular glycogen, protein and RNA content during the differentiation of such myxamoebae were determined. 2. Myxamoebal glycogen is not conserved during differentiation and gluconeogenesis may occur even in cells that contain a large amount of glycogen initially. 3. There is a marked net loss of cellular protein and RNA during differentiation and associated with this there are also marked decreases in the sizes of the intracellular pools of amino acids, acid-soluble proteins and pentose-containing materials. 4. During the early stages of development some protein and pentose(s) are excreted, but this cannot account for the decreased cellular content of protein and RNA. 5. There is a linear rate of production of NH(3) during development, and oxidation appears to be the fate of the major portion of the degraded protein and RNA. 6. However, provision of an alternative metabolizable energy source (glycogen) has little effect on the rate or extent of protein or RNA breakdown or on the changes in the sizes of the intracellular pools of amino acids, acid-soluble proteins and pentose-containing materials. 7. It is concluded that during development there is a requirement for the destruction of specific RNA and protein molecules for reasons other than the provision of oxidizable substrates. 8. The kinetic model of Wright et al. (1968) is discussed in relation to these changes in macromolecular content.
TL;DR: Phenotypic revertants to fructose tolerance have lost either the histidine-containing protein (HPr) or enzyme I of the phosphoenolpyruvate phosphotransferase system (ctr), and consequently utilize neither fructose nor glucose, or an enzyme II specific for the uptake of fructose and its concomitant phosphorylation to fructose 1-phosphate (PtsF).
Abstract: Mutants of Escherichia coli impaired in fructose 1-phosphate kinase activity (Fpk) accumulate fructose 1-phosphate from fructose, which arrests their growth Phenotypic revertants to fructose tolerance have lost either the histidine-containing protein (HPr) or enzyme I of the phosphoenolpyruvate phosphotransferase system ( ctr ), and consequently utilize neither fructose nor glucose, or an enzyme II specific for the uptake of fructose and its concomitant phosphorylation to fructose 1-phosphate (PtsF) However, PtsF — -mutants can still grow on high concentrations ( > 2 mM) of fructose, and take up this sugar via a low-affinity enzyme II designated PtsX that effects its uptake and phosphorylation to fructose 6-phosphate Mutants of the Hfr-strain KL16 were isolated that lacked PtsF, or PtsF and PtsX, activities The consequence to, and role of these functions in, the uptake and metabolism of fructose are described
TL;DR: It seems that the ischemic kidney sustains hypertension in this two-kidney model through activity of the renin-angiotensin system, although extrarenal factors assume greater importance when blood pressure remains elevated for longer periods.
Abstract: Factors responsible for maintaining blood pressure were studied in rats with one renal artery constricted and the contralateral kidney intact. Rats with short-term ( 4 months) hypertension were infused with angiotensin II antiserum until the pressor effect of exogenous angiotensin II was blocked. The blood pressure response to an infusion of an angiotensin antagonist (1-Sar-8-Ala-angiotensin II) was then recorded. Blood pressure was also measured following subsequent unilateral nephrectomy (ischemic kidney). Antiserum produced a small, sustained, nonsignificant fall in mean blood pressure, whereas the antagonist produced a major reduction. In rats with short-term hypertension, the antagonist reduced blood pressure to normal or near-normal levels. In rats with chronic hypertension, mean blood pressure fell but still remained above the upper limit of the normal range. Removal of the ischemic kidney produced a fall in blood pressure to a mean level close to that obtained after antagonist infusion. Mean cumulative sodium balance in the rats with short-term hypertension was slightly negative. On the basis of this and previously reported work, it is suggested that angiotensin II is generated at a vascular site which is inaccessible to antibody but readily accessible to antagonist. Moreover, since the effects of angiotensin II antagonist and nephrectomy do not differ significantly, it seems that the ischemic kidney sustains hypertension in this two-kidney model through activity of the renin-angiotensin system, although extrarenal factors assume greater importance when blood pressure remains elevated for longer periods.
TL;DR: In this paper, the capabilities of microchannel plate converters for position sensitive detectors for use at lower quantum energies and better position resolution than can be realized using present gas and silicon event-to-charge converters are discussed.
TL;DR: The fluids and melts responsible for the crystallisation of rocks and minerals may be trapped and preserved as small inclusions within a crystal, providing much information about the physical and chemical conditions prevailing during crystallisation as discussed by the authors.
Abstract: PORTIONS of the fluids and melts responsible for the crystallisation of rocks and minerals may be trapped and preserved as small inclusions within a crystal, providing much information about the physical and chemical conditions prevailing during crystallisation1,2.
TL;DR: A solution is given to the problem: Can 15 schoolgirls walk out in five rows of three, seven times a week for a term of 13 weeks, in such a way that any two girls are in the same row just once in each week, and any three just twice in the term.
TL;DR: Cell division was synchronised in 4-litre batch cultures of Acer pseudoplatanus L. by starvation and regrowth; the final rate being twice that observed initially.
Abstract: Cell division was synchronised in 4-litre batch cultures of Acer pseudoplatanus L. by starvation and regrowth. Up to five consecutive cell cycles were observed in each culture. Mitosis and cytokinesis were synchronised within 0.2 cell cycles. Accumulation of extractable DNA was discontinuous and separate from cytokinesis. Correction for the degree of synchrony in the population gave: G1=13–37 h, S=15 h, G2=14–19 h and M=0.9–1.3 h. Thymidine kinase activity and [14C]thymidine incorporation were highest during S-phase. A peak of activity of aspartate transcarbamoylase occurred during G2. Peaks in succinate dehydrogenase activity and respiration rate were observed at the initiation of DNA synthesis and just prior to mitosis. The activity of glucose-6-phosphate dehydrogenase doubled in one step during the cell cycle. Total RNA and protein accumulated continuously through the cell cycle; the final rate being twice that observed initially.
TL;DR: The seasonal changes in the enzyme-substrate affinity are consistent with the known seasonal glycolytic and gluconeogenic sequence in the mantle and could proceed together, with the predominancer of one reaction over the other being determined by the degree of tissue hypoxia.
Abstract: 1. 1. Mantle pyruvate kinase (E.C.2.7.1.40) is subject toa allosteric regulation, being inhibited by l -alanine and ATP and activated by fructose- 1,6-diphosphate (FDP). 2. 2. Substrate dependence of the enzyme is sigmoidal, and the sigmoidicity is increased at low pH. 3. 3. FDP at physiological concentrations overrides inhibition of the enzyme by l -alanine. 4. 4. The result of these modulators acting together suggests that both the reaction catalysed by pyruvate kinase (PEP → pyruvate) and the reaction catalysed by phosphoenolpyruvate carboxykinase (PEP → oxoloacetate) could proceed together, with the predominancer of one reaction over the other being determined by the degree of tissue hypoxia. 5. 5. The seasonal changes in the enzyme-substrate affinity are consistent with the known seasonal glycolytic and gluconeogenic sequence in the mantle.
TL;DR: Indol-3yl-acetic acid was identified in extracts of sterile roots of Zeamays seedlings by means of TLC, chromogenic reactions, GLC and GC-MS as mentioned in this paper.
TL;DR: Catalysis by pure ribulose bisphosphate carboxylase from Rhodospirillum rubrum, which is a dimer lacking small subunits, is inhibited by oxygen, indicating a competitive inhibitor with respect to carbon dioxide.
TL;DR: Inorganic orthophosphate inhibition appeared to be more complex and was overcome in a co-operative manner by increasing dihydroxyacetone phosphate concentration, and Hill plots suggested that in the presence of inorganic orthphosphate there were three diHydroxyacet one phosphate-binding sites on the enzyme.
Abstract: Methylglyoxal synthase, which forms methylglyoxal from dihydroxyacetone phosphate, has been detected in both glucose- and succinate-grown Pseudomonas saccharophila but there was no evidence for methylglyoxal production from d-glyceraldehyde. The enzyme was purified 100-fold from glucose-grown cells and found to be very similar to Escherichia coli methylglyoxal synthase. It has a pH optimum of 8.2, a molecular weight of approximately 67000 and a Km for dihydroxyacetone phosphate of 0.09 mM. Inorganic pyrophosphate, 3-phosphoglycerate, phosphoenol-pyruvate and inorganic orthophosphate were all potent inhibitors, the first three compounds being competitive with respect to dihydroxyacetone phosphate with K1 values of 0.048 mM, 0.029 mM and 0.096 mM, respectively. Inorganic orthophosphate inhibition appeared to be more complex and was overcome in a co-operative manner by increasing dihydroxyacetone phosphate concentration. Hill plots suggested that in the presence of inorganic orthophosphate there were three dihydroxyacetone phosphate-binding sites on the enzyme.
TL;DR: In this paper, information relating to the selection of configuration geometry, control devices and materials for both gas and liquid feed bearings is included. And guidance is given concerning the achievement of total system reliability.
TL;DR: The genes that specify the activities of the components of the phosphoenolpyruvate- phosphotransferase system that mediate the conversion of fructose to fructose 1-phosphate and to fructose 6-ph phosphate have been located on the genome of Escherichia coli at minutes 41 and 35.5 respectively.
Abstract: The genes that specify the activities of the components of the phosphoenolpyruvate-phosphotransferase system that mediate the conversion of fructose to fructose 1-phosphate (ptsF) and to fructose 6-phosphate (ptsX) have been located on the genome of Escherichia coli at minutes 41 and 35.5 respectively. The gene specifying fructose 1-phosphate kinase activity (fpk) has also been mapped; it is highly cotransducible with ptsF.