Showing papers by "King's College London published in 1971"
TL;DR: The structure of the purple membrane and its localization in the bacterial cell envelope are described and it is shown that it contains retinal bound in a mole ratio of 1 : 1 to a protein of molecular weight 26,000 which is the only protein present.
Abstract: IN the preceding article1 it has been shown that a cell membrane fragment, the purple membrane, isolated from Halobacterium halobium2 contains retinal bound in a mole ratio of 1 : 1 to a protein of molecular weight 26,000 which is the only protein present. We now describe the structure of the purple membrane and its localization in the bacterial cell envelope.
413 citations
TL;DR: X-ray diffraction studies show that lipid hydrocarbon chains are uniformly packed in bilayers and oriented so that their free ends are near the centre, which provides a model for biological membranes.
Abstract: X-ray diffraction studies show that lipid hydrocarbon chains are uniformly packed in bilayers and oriented so that their free ends are near the centre. This provides a model for biological membranes.
350 citations
TL;DR: Diffraction analysis of dispersions of membranes makes it possible to study membranes not in regular arrays and shows that a phospholipid bilayer is a predominant structural component of membranes with various different functions.
Abstract: Diffraction analysis of dispersions of membranes makes it possible to study membranes not in regular arrays. Such analysis shows that a phospholipid bilayer is a predominant structural component of membranes with various different functions.
295 citations
TL;DR: X-ray diffraction patterns from intact, isolated Mycoplasma laidlawii membranes at temperatures above and below the thermal phase transition of the membrane lipids reveal important features of the molecular structure of the membranes.
233 citations
TL;DR: Ferredoxins have been found in a wide range of organisms, from the primitive anaerobic bacteria to all higher plants and animals, and a knowledge of the changes in their amino-acid sequence is of great value to the study of the evolution of these organisms.
Abstract: THE ferredoxins are members of a class of metalloproteins known as iron–sulphur proteins which act as electron carriers in such diverse biochemical processes as carbon metabolism, nitrogen fixation, photosynthesis and steroid hydroxylation1,2. They are relatively small proteins with molecular weights of 6,000 to 12,000; they contain 2–8 atoms of iron and equivalent amounts of inorganic sulphur per molecule, transferring electrons at low redox potentials (−300 to −500 mV at pH 7) and having a characteristic electron paramagnetic resonance signal at g= 1.94 in the reduced state. Ferredoxins have been found in a wide range of organisms, from the primitive anaerobic bacteria to all higher plants and animals. A knowledge of the changes in their amino-acid sequence3 is therefore of great value to the study of the evolution of these organisms.
143 citations
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140 citations
TL;DR: Three prostaglandin antagonists have been examined for their ability to block PGE2 and PGF2α on human, guinea‐pig and isolated rat gastrointestinal muscle, and the value of each compound as a prostaglandsin antagonist is discussed.
Abstract: 1. Three prostaglandin antagonists have been examined for their ability to block PGE(2) and PGF(2alpha) on human, guinea-pig and isolated rat gastrointestinal muscle.2. 7-oxa-13-Prostynoic acid was either a non-selective antagonist, or was ineffective on the tissues studied; it had marked spasmogenic activity on the rat fundus.3. 1-Acetyl-2-(8-chloro-10,11-dihydrodibenz (b,f)(1,4) oxazepine-10-carbonyl) hydrazine selectively antagonized the excitatory effects of PGE(2) and PGF(2alpha) in guinea-pig and rat tissues, but not in human muscle.4. Polyphloretin phosphate selectively antagonized the excitatory effects of prostaglandins in both human and guinea-pig muscle preparations, but it caused stimulation of the rat fundus.5. All the antagonists lowered the tone in many tissues. They also reduced contractions caused by potassium.6. None of the compounds blocked the inhibitory effect of PGE(2) on intestinal circular muscle.7. The implication of these results on the nature of prostaglandin receptors, and the value of each compound as a prostaglandin antagonist are discussed.
139 citations
TL;DR: It is argued that because the former mechanism is essentially macroscopic in character it cannot, in fact, be used in those biological processes, like muscular contraction or active transport, in which useful molecular work is done and that only the latter may be so used.
134 citations
TL;DR: It is suggested that the way in which the molecules are packed is common to all types of myosin filament, which leads to quantitative predictions about the component molecules.
Abstract: It is suggested that the way in which the molecules are packed is common to all types of myosin filament. This leads to quantitative predictions about the component molecules.
80 citations
TL;DR: The differences in development between larval and adult teeth support the concept that there is a change in cellular activity of the i.d.e which occurs during metamorphosis from the larval to the adult urodele.
Abstract: Sections of undemineralized tooth germs ofAmbystoma andTriturus were examined. The ultrastructure of early germs, both larval and adult, and of dentinogenesis, resembled that of mammals. In adult bicuspid teeth, once the dentine of the cusps was mineralized, mineral crystals of a similar size to early mammalian enamel crystals, appeared between the dentine and the inner dental epithelium (i.d.e). Concomitantly, the i.d.e showed features of mammalian secreting ameloblasts. This new layer, regarded as true enamel, lacked collagen, possessed an ordered arrangement of crystals and reached a maximum thickness of 6 μm.
79 citations
TL;DR: In this paper, the development of increased activities of ribulosediphosphate carboxylase (EC 4.7.1.19) in greening bean leaves was completely inhibited by D-threo chloramphenicol but unaffected by L-threeo chlorAMPhenicol, where both specific and unspecific (both isomers) inhibition occurred.
Abstract: The development of increased activities of ribulosediphosphate carboxylase (EC 4.1.1.39) and of phosphoribulokinase (EC 2.7.1.19) in greening bean leaves was completely inhibited by D-threo chloramphenicol but unaffected by L-threo chloramphenicol. This indicates that these enzymes are synthesized by the ribosomes of the developing plastids. A different mechanism appears to be responsible for the development of activity of NADP-dependent triosephosphate dehydrogenase (EC 1.2.1.13) where the D-threo isomer gave 45% inhibition and the L-threo isomer gave 18% inhibition. Thus both specific (D-threo isomer) and unspecific (both isomers) inhibition occurred. It is suggested that the development of NADP-dependent triosephosphate dehydrogenase activity may result from the allosteric activation, in the plastids, of the NAD-dependent enzyme (Muller et al., 1969) which has been synthesized by cytoplasmic ribosomes. Neither isomer inhibited the development of five other enzymes of the photosynthetic carbon cycle namely ribosephosphate isomerase (EC 5.3.1.6), phosphoglycerate kinase (EC 2.7.2.3), triosephosphate isomerase (EC 5.3.1.1), tructosediphosphate aldolase (EC 4.1.2.13) and transketolase (EC 2.2.1.1), but there was a significant stimulation of the activity of transketolase by D-threo chloramphenicol.
TL;DR: The observations that deoxyhaemoglobin has a single strong binding site for the cofactor, which in consequence stabilizes it in relation to the oxygenated state can be explained qualitatively by observations that the binding site is associated with the β chains.
Abstract: THE oxygen affinity of haemoglobin is profoundly affected by the presence of low concentrations of organic phosphates, in particular 2,3-diphosphoglycerate (DPG)1–5. This phenomenon, which has now been widely recognized as a physiologically vital control mechanism6–10, can be explained qualitatively by our observations2 that deoxyhaemoglobin has a single strong binding site for the cofactor, which in consequence stabilizes it in relation to the oxygenated state. The binding site is associated with the β chains11 and it has been identified as the cavity at the conjunction of the N-termini of these chains5,12–18, lying therefore on the dyad axis of the tetramer.
TL;DR: Fundamental differences between the diffusion process in simple liquids and that in more complex media-non-porous networks of hydrophobic polymers and biological membranes are drawn attention.
Abstract: AS it is not widely appreciated that diffusion within complex media can be strikingly and often qualitatively different from that in simple liquids such as water, there is confusion concerning transport processes across biological membranes1,2. We would like to draw attention to some fundamental differences between the diffusion process in simple liquids and that in more complex media-non-porous networks of hydrophobic polymers and biological membranes.
TL;DR: There was a considerable rise in endogenous gibberellins on transfer to 20°, this rise preceding the detection of measurable growth of the embryonic axis, and this rise was several hundred-fold greater than that in the cotyledons.
Abstract: Summary. The endogenous gibberellins of hazel seeds have been studied by a thin layer chromatography/pea epicotyl bioassay (TLC/bioassay) procedure and also by gas-liquid chromatography (GLC) of the gibberellin methyl esters and the trimethylsilyl ethers of the methyl esters. Consistent results were obtained from the two techniques and provisional identifications of some of the gibberellins were obtained by GLC. The gibberellin which was present in the newly harvested seeds, which do not show embryo dormancy, had largely disappeared after the develop ment of embryo dormancy. During 28 days chilling at 5° there was a small increase in endogenous gibberellin but on transfer to 20° there was a considerable rise in endogenous gibberellins, variously estimated as 64-fold (GLC) or 79-fold (TLC/bio assay), this rise preceding the detection of measurable growth of the embryonic axis. The GLC procedure gave provisional identifications of GAj, GA4 and/or GA7, GA5 and/or GA20, GA6 and/or GA17, and GAg. The gibberellin concentration in the embryonic axis was several hundred-fold greater than that in the cotyledons.
TL;DR: Empirical formulas are presented which relate the mobility of an RNA species to its molecular weight or Stokes radius and to the concentration of the gel, consistent with recent theories of the effect of gel concentration on electrophoretic mobilities.
TL;DR: In this paper, a number of newly discovered luminescence bands between ≈ 0.7 eV and ≈ 2.2 eV which appear to be characteristic of diamonds possessing various concentrations and configurations of the major impurity, nitrogen, were identified with the radiative recombination of free holes with electrons in the platelet nitrogen donor impurity band.
TL;DR: Cell-free extracts with high nitrogenase activity were prepared by sonic oscillation and French press treatment from the blue-gree alga Anabaena cylindrica and activity was found to be dependent on adenosine triphosphate (ATP), an ATP-generating system, and a low-potential reductant.
Abstract: Cell-free extracts with high nitrogenase activity were prepared by sonic oscillation and French press treatment from the blue-gree alga Anabaena cylindrica. Extracts were prepared from cells grown on a 95% N(2)-5% CO(2) gas mixture followed by a period of nitrogen starvation under an atmosphere of 95% argon-5% CO(2). No increase in the specific activity of extracts was achieved by breaking heterocysts. Activity (assayed by acetylene reduction) was found to be dependent on adenosine triphosphate (ATP), an ATP-generating system, and a low-potential reductant. Na(2)S(2)O(2) employed as reductant supports higher rates of nitrogenase activity than reduced ferredoxin. The activity is associated with a small-particle fraction that can be sedimented by ultracentrifugation. In contrast to the particulate nitrogenase of Azotobacter, which is stable in air, the A. cylindrica nitrogenase is an oxygen sensitive as nitrogenase prepared from anaerobic bacteria.
TL;DR: In this article, a semi-espace de terrain isotrope, elastique, and incompressible, where le module de cisaillement accroit lineairement avec la profondeur, partant de zero a la surface, reagit a la charge superficielle exactement selon les hypotheses faites par Winkler dans sa theorie de la reaction du niveau de fondation.
Abstract: On sait qu'un semi-espace de terrain isotrope, elastique et incompressible — dont le module de cisaillement accroit lineairement avec la profondeur, partant de zero a la surface — reagit a la charge superficielle exactement selon les hypotheses faites par Winkler dans sa theorie de la reaction du niveau de fondation. On examine ici jusqu'a quel point la validite de ce resultat s'applique a un milieu de profondeur limitee. On y demontre que, si la profondeur de la couche depasse la largeur de la surface chargee, le tassement d'une charge repartie uniformement est aussi pratiquement uniforme. Cependant, au dela du sol charge, la surface se souleve d'une maniere sensible, meme lorsque la couche est d'une epaisseur moderee.
TL;DR: The puromycin reaction is utilised to elucidate the mechanisms of action of two antibiotics thiostrepton and elythromycin and assays the distribution of peptidyl-tRNA between sites A and P in a given ribosome population.
TL;DR: Spinach chloroplasts, isolated rapidly in isotonic media will reproducibly give photosynthetic control rates of 4–6, and ADP/O ratios of 1.4 – 2.1 when assayed in slightly hypotonic media.
TL;DR: Glucose transport in the human red blood cell may proceed by internal transfer across a protein tetramer, and this model could account for transport phenomena in other systems.
Abstract: Glucose transport in the human red blood cell may proceed by internal transfer across a protein tetramer. Such a model could account for transport phenomena in other systems.
TL;DR: In this paper, a particular lattice Green function for the face centred cubic lattice with anisotropic nearest neighbor interactions is evaluated exactly as a product of two complete elliptic integrals.
Abstract: A particular lattice Green function for the face centred cubic lattice with anisotropic nearest neighbour interactions is evaluated exactly as a product of two complete elliptic integrals. Applications of this result in lattice statistics are briefly described.
TL;DR: Native and reaggregated membranes from Mycoplasma and erythrocytes have been compared using the fluorescence probe 1-anilinonaphthalene-8-sulphonate (ANS) to show that it is the membrane proteins which are incorrectly reassembled in the reaggRegated structures, whereas techniques which provide information about the lipid bilayer in theReaggregation structure show that this is relatively insensitive to the conformational state of the proteins.
TL;DR: Reaggregates of Mycoplasma membranes after dispersion in sodium dodecyl sulphate were indistinguishable structurally from native membranes by the criteria of composition, density, and electron microscopy, implying that the membranes have a common element of structural organisation.
TL;DR: Monitoring of the shrimp catch off West Thurrock in the Thames estuary shows that they occur from September to February–April, but that within this period they are subject to great fluctuations, and a model of shrimp migration suggested.
TL;DR: Nitrogenases from Anabaena cylindrica and Chloropseudomonas ethylicum were partially purified into two components and the reciprocal cross between C. ethy Licum fraction I and A. cylindica fraction II was negative.
Abstract: Nitrogenases from Anabaena cylindrica and Chloropseudomonas ethylicum were partially purified into two components. A. cylindrica fraction I protein complemented fraction II protein from C. ethylicum. However, the reciprocal cross between C. ethylicum fraction I and A. cylindrica fraction II was negative.