Hypotensive constituents of marine algae; 1. Pharmacological studies of laminine.
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Animals↗
Biomedical subjects
C Marion
Publications and source records attributed to C Marion.
The essential oil of Hyptis pectinata.
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Oils, Volatile↗
Localization of ribosomal proteins on the surface of mammalian 60S ribosomal subunits by means of immobilized enzymes. Correlation with chemical cross-linking data.
Trypsin covalently bound on collagen membranes has been used to investigate the protein topography in eukaryotic 60S ribosomal subunits. Six proteins are highly exposed to the attack of the immobilized enzyme: L6, L7-L7a, L17, L24, and L31. They are located in two distinct regions, forming two bulges at the ribosomal surface; the first one consists of proteins L6 and L7-L7a, which are screening proteins degraded later, as L4, L14, L23a, and L29; the second one is formed by proteins L17, L24, and L31, which are shielding L19 and L22. L3, L5, L8, L11, L12, L26, L30, L34, and L37a, are located in a trough between the two bulges. L10, close to L5, appears to be more accessible than all these proteins. Several proteins are not degraded by trypsin, even for a very long time of incubation: L9, L13-L13a, L18, L18a, L21, L25, L27-L27a, L28, L32, L35, L35a, L36-L36a, and L38. The cross-linking data suggest that these latter proteins are mainly protected by the proteins located in the L6-L7-L7a region, and by the 28S RNA. A model of protein topography within the 60S rat liver subunits, based on protein accessibility and cross-linking data, is proposed.
Animals↗
H3 phosphorylation-dependent structural changes in chromatin. Implications for the role of very lysine-rich histones.
Contrary to native H1/H5-containing chromatin where phosphorylation induces local structural changes affecting chromatin condensation, in stripped fibers phosphorylation of the totality of H3 molecules does not affect significantly chromatin conformation and DNA-protein interactions. Modification of H3 causes only a slight increase of flexibility of nucleosomal chains, despite important changes in histone topography revealed by immunochemical reactivity studies. We suggest that phosphorylation may only induce into the system the potential for dynamic change by modulating histone-histone interactions within and between nucleosomes, probably as a result of conformational change in the H3 protein. The signal for structural change would come from one or other factors (very lysine-rich histones, non-histones) that influence internucleosomal interactions at very specific locations in the chromatin, probably through protein-protein contacts. So, phosphorylation may modify a direct interaction between the N-terminal basic tail of H3 and very lysine-rich histones.
Birefringence↗
Structural aspects and orientation mechanism of mitochondrial F1 adenosinetriphosphatase. Evidence for a negative electric birefringence due to a permanent moment perpendicular to the long axes of the particle.
The electric birefringence technique was used to investigate the steady-state birefringence, the orientational relaxation time, and the orientation mechanism of pig heart mitochondrial F1 adenosine-5'-triphosphatase (F1-ATPase). The electrooptical properties of this enzyme in solution were studied as functions of pH, protein concentration, and applied electric field. The F1-ATPase exhibits a surprising negative electric birefringence with a specific Kerr constant of -1.5 X 10(-3) esu cgs. The field-independent relaxation time was found to be 0.65 +/- 0.05 microseconds, corresponding to a rotational diffusion constant of 2.55 X 10(5) s-1. The overall size and shape of F1-ATPase have been calculated from both translational and rotational diffusion constants. The enzyme may be assumed to be an oblate ellipsoid of revolution with dimensions of about 170 X 170 X 70 A. The orientation mechanism of F1-ATPase was analyzed by fitting experimental birefringence rising curves with theoretical rising functions. The ratio of the permanent to induced dipole moment is found to be very high; therefore, the birefringence of F1-ATPase is due to a strong permanent dipole moment in a direction perpendicular to the long axes of the particle. These particular electric properties can be explained by the oligomeric structure of the protein and seem likely to play a role in its mechanism of functioning.
Animals↗
DNA polymorphism: spectroscopic and electro-optic characterizations of Z-DNA and other types of left-handed helical structures induced by Ni2+.
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DNA↗
Effects of arm ergometry training in an adolescent with myelodysplasia. A case report.
The purpose of this article is to report the effects of arm ergometry training on upper extremity strength, body composition, and oxygen uptake in a 13-year-old adolescent with myelodysplasia. The subject trained three times a week for eight weeks at 75% of maximum heart rate. The following measurements were determined before and after the training period: maximal and submaximal heart rate and oxygen uptake, percent body fat, and peak torque of the elbow and shoulder flexor and extensor muscles. The results indicated that maximal oxygen uptake and percent body fat did not change, but maximal physical work capacity increased from 274 kg . m/min to 569 kg X m/min. Heart rate and oxygen uptake decreased at each submaximal work load, and peak torque increased an average of 22.3% for the movements tested. We concluded that arm ergometry training in an adolescent with myelodysplasia can reduce the energy cost of performing submaximal arm ergometry work.
Adipose Tissue↗
Histone phosphorylation in native chromatin induces local structural changes as probed by electric birefringence.
In order to understand how the phosphorylation of histones affects the chromatin structure, we used electron microscopy, sedimentation velocity, circular dichroism and electric birefringence to monitor the salt-induced filament reversible solenoid transition of phosphorylated and native chromatin. Phosphorylation in vitro of chicken erythrocyte chromatin by cyclic-AMP-dependent protein kinase from porcine heart led to the modification of the histones H3 and H5 only, which were modified at a level of one phosphate and about three phosphate groups per molecule, respectively. In contrast to circular dichroism and sedimentation studies, which tend to suggest that phosphorylation of H3 and H5 does not affect chromatin structure, electron microscopy reveals that phosphorylation causes a relaxation of structure at low ionic strength. Electric birefringence and relaxation time measurements clearly prove that local structural changes are induced in chromatin: we observe a decrease of the steady-state birefringence with the appearance of a negative contribution in the signal and a marked increase of the flexibility of fibres. The component with the negative birefringence presents very short relaxation times, like those exhibited by small DNA fragments or individual nucleosomes. Two possibilities are then suggested. First, the conformational change is consistent with what would be expected from the presence of DNA segments loosely associated with the core histone H3. That the length of such segments could correspond to about one to two base-pairs per nucleosome strongly suggests that phosphorylation induces changes affecting some specific H3-DNA interactions only. This result could corroborate previous observations indicating that the N-terminal region of H3, where the site of phosphorylation is located, plays a decisive role in maintaining the superstructure of chromatin. Second, phosphorylation could introduce hinge points between each nucleosome. In this case, the negative birefringence results from partial orientation of the swinging nucleosomes. A possible mode of action of phosphorylation might be to weaken structural restraints imposed by histone H3, thus facilitating further condensation of chromatin.
Animals↗
Differences in the condensation of chromatin by individual subfractions of histone H1: implications for the role of H1(0) in the structural organization of chromatin.
The effectiveness of histone H1 subfractions H1-1 and H1(0) in inducing the ordered condensation of chromatin was examined by thermal denaturation, circular dichroism, electric birefringence, orientation mechanism, and orientational relaxation time measurements. Soluble rat liver chromatin was stripped of H1 by dissociation in 500 mM NaCl and long fragments of chromatin were subsequently reassociated with purified individual H1 subfractions for ratios of 1 and 2 mol of H1 per nucleosome. H1 subfractions behave differently with respect to their interactions with DNA in chromatin: although the orientation mechanisms of reconstituted chromatins are identical, H1(0) induces a less efficient protection of DNA than H1-1, as shown by nuclease digestion and by the length of free extended linker DNA determined by electric birefringence. This corresponds to a more extended structure of H1(0)-reconstituted chromatin as judged by the value of relaxation time. One can imagine that the replacement of H1 by H1(0) leads to a different structure or stability of the chromatin, confering a certain degree of flexibility of this region. This may be related to the functional role of H1(0) in DNA replication or transcription and may explain metabolic and evolutionary differences among H1 subfractions as recently suggested by Lennox [Lennox, R. W. (1984) J. Biol. Chem. 259, 669-672]. The extent of condensation when H1-depleted chromatin is overloaded with histones is probably a function of the electrostatic interactions between the basic C-terminal tails of histones and chromatin. Electric birefringence also reveals differences between native and reconstituted chromatins that are overlooked by several other criteria.
Animals↗
The effect of histone H1 on the compaction of oligonucleosomes. A quasielastic light scattering study.
The structural properties of H1-depleted oligonucleosomes are investigated by the use of quasielastic laser light scattering, thermal denaturation and circular dichroism and compared to those of H1-containing oligomers. To obtain information on the role of histone H1 in compaction of nucleosomes, translational diffusion coefficients (D) are determined for mono-to octanucleosomes over a range of ionic strength. The linear dependences of D on the number of nucleosomes show that the conformation of stripped oligomers is very extended and does not change drastically with increasing the ionic strength while the rigidness of the chain decreases due to the folding of linker DNA. The results prove that the salt-induced condensation is much smaller for H1-depleted than for H1-containing oligomers and that histone H1 is necessary for the formation of a supercoiled structure of oligonucleosomes, already present at low ionic strength.
Animals↗
Higher order structure of chromatin: influence of ionic strength and proteolytic digestion on the birefringence properties of polynucleosomal fibers.
Effects of ionic strength and proteolytic digestion on the conformation of chromatin fibers were studied by electric birefringence and relaxation measurements. The results confirm that at low ionic strength chromatin presents structural features reflecting those observed in the presence of cations. Soluble chromatin prepared from rat liver nuclei by brief nuclease digestion exhibits a positive birefringence. As the salt concentration is increased, the transition to a compact solenoidal structure is deduced from changes in electro-optical properties: the positive birefringence gradually decreases and the observed reduction in 40 mM NaCl is nearly 95%; the relaxation time decreases dramatically and the character of the kinetic changes since the decay of birefringence described initially by a spectrum of relaxation times becomes monoexponential. On digestion with proteases at low ionic strength we observe at first a rapid increase of the positive birefringence concomitant with an increase of the relaxation time. Then the birefringence decreases and becomes negative. Chromatin undergoes two successive transitions: the first transition is explained by a lengthening of nucleosomal chains without modification of the orientation of nucleosomes within the superstructure and the second one by the unwinding of the DNA tails and internucleosomal segments. When chromatin is digested at 30 mM NaCl we find a single unfolding transition characterized by the decrease of birefringence and a slight increase in the relaxation time. The results imply that the positive birefringence of chromatin does not depend on the presence of whole histone H1 and that a salt concentration of 30 mM NaCl is sufficient to modify the initial site or/and the effects of proteolytic attack.
Animals↗
Non-specific binding of heat-aggregated IgG to histone detected by ELISA.
Anti-histone antibodies are currently detected by micro ELISA in systemic lupus erythematosus sera from humans, mice and dogs. Here we show that the control-heated sera may bind non-specifically to the whole histones and histone fractions. The heated immunoglobulins binding to histones are mainly IgG and to a lesser extent IgA, but never IgM. These false positive ELISA reactions occurred only with aggregated IgG which binds to histones via Fc; IgM rheumatoid factor prevented their fixation. Immune complexes do not seem to interfere significantly in the detection of anti-histone antibodies with the ELISA test.
Antibodies↗
Electric birefringence of chromatin reconstituted with various histone H1 subfractions.
Rat liver chromatin is stripped of H1 histone by exposure to 0.5 M NaCl and reassociated with individual purified subfractions of H1 by salt-step dialysis. The effectiveness of proteins H1-1 and H1 in the condensation of DNA is monitored by transient electric birefringence and circular dichroism. Steady-state birefringence and relaxation time measurements show that reconstitutions are not perfect although some features of native chromatin are restored when a ratio of 2 moles of H1 per nucleosome is used. The amplitude of the positive birefringence is better recovered with H1-1 than with H1 but the values of relaxation times and molar ellipticities indicate that reconstituted samples exhibit a more compact and rigid structure compared to that of native chromatin.
Animals↗
Electric birefringence of eukaryotic ribosomes.
Eukaryotic 60S ribosomal subunits were studied by transient electric birefringence. Conformations of subunits in active and inactive states upon changes in magnesium concentration were compared by electric birefringence and orientational relaxation time measurements. Active subunits exhibit a positive birefringence and a relaxation time of the order of 8 microseconds. In the presence of EDTA, inactive subunits show no birefringence. When Mg2+ is reverted in the cold to its initial level, the electro-optical properties of the subunits are partially restored although the particles remain biologically inactive.
Animals↗
Structural properties of barley nucleosomes.
The structural properties of barley oligonucleosomes are investigated and compared to those of rat liver oligomers. Extraction of barley chromatin was performed using mild nuclease digestion of isolated nuclei leading to a low ionic strength soluble fraction. Oligonucleosomes were fractionated on sucrose gradients and characterized for DNA and histone content. Physico-chemical studies (sedimentation, circular dichroism and electric birefringence) showed that barley oligonucleosomes exhibit properties very close to those of the H1-depleted rat liver counterparts. Moreover, in situ, barley linker DNA was more sensitive to micrococcal nuclease digestion than that of rat liver. These results suggest that barley oligonucleosomes show a less compact structure than their rat liver counterparts and appear to be in contradiction with the very condensed organization of barley chromatin previously suggested.
Journal Article↗
The structural organization of oligonucleosomes.
We have used electric birefringence to study the structure of oligonucleosomes and to show the influence of histone H1 depletion on their conformation in solution. Measurements are made at low ionic strength on monodisperse samples containing up to 8 nucleosomes. For each oligomer, having H1 or not, the analysis of both relaxation and orientation times gives information about the particle's orientation mechanism through the ratio r of permanent over induced dipole terms. For native oligomers, the data confirm the previous finding of a discontinuity in hydrodynamic behavior between pentamer and heptamer: the rotational times are multiplied by 10 and r increases from 0.2 to 0.7 showing the appearance of a non-negligible contribution of a permanent dipole to the orientation mechanism. We suggest a model for the hexanucleosome at low ionic strength and discuss its implications for the higher-order structure of chromatin. The treatment for H1 depletion abolishes the transitions in electro-optical properties: the value of r remains constant, r = 0.15, and both rotational times increase progressively with the number of nucleosomes in the chain. That reflects an important unfolding of oligonucleosomal structure which we attributed to the unwinding of DNA tails and internucleosomal segments. The disc planes of nucleosomes become closely parallel to the nucleosomal chain axis.
Animals↗
Study of chromatin organization with trypsin immobilized on collagen membranes.
Trypsin immobilized on collagen membranes has been used to digest chromatin polynucleosomes. With this method, the use of protease inhibitor is avoided and the digestion time easily controlled simply by taking the membrane out of the chromatin solution. Its most fundamental advantage is however to allow the mild removing of the most accessible histone fragments without addition of salt then without perturbation of their ionic environment. Degradation of histone fractions were correlated with conformational changes using circular dichroism and electric birefringence measurements. On digestion, the sign of birefringence reversed, becoming negative, and an increase of molar ellipticity was observed. These changes reflecting the unfolding of DNA correspond to the digestion of Hl and also of fragments of H3. This would indicate that H3 and particularly its basic terminal regions, play a fundamental role in the maintenance of chromatin in a compact structure.
Animals↗
Role of histones H1 and H3 in the maintenance of chromatin in a compact conformation. Study with an immobilized enzyme.
Chromatin polynucleosomes have been digested with trypsin immobilized on collagen membranes. This method allows the mild removal of the most accessible histone fragments simply by dipping the enzymatic membrane into the chromatin solution, without modification of its ionic and chemical composition. These results demonstrate that the removal of H1 does not affect the higher-order structure of chromatin and that only the elimination of the terminal regions of H3 leads to the unfolding of H1-depleted fibres. This observation suggests that structural changes reported in many previous works were not due to only the removal of H1 but to a concomitant unbinding from DNA of the N-terminal domain of H3.
Animals↗