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At least 19 recordsLinked to original sources
PubMed1978

Birefringence of oriented thin filaments in the I-bands of crab striated muscle and comparison with the flow birefringence of reconstituted thin filaments.

Birefringence of the I-band of glycerinated myofibrils of the walking legs of the crab, Plagusia dentipes was examined by rectified polarization optics. The coefficient of birefringence of the I-band was estimated to be 1.64 X 10(-3), which attained about 60% of the birefringence of the H-zone. The number ratio of thin filaments to thick filaments in the A-band was six according to electron microscopy and the spacing between neighbouring thick filaments was about 56 nm according to X-ray diffraction. From these values, the protein concentration in the I-band was estimated to be 91 mg/ml. Thus, the birefringence of the I-band was found to be of the same order as the birefringence of the reconstituted thin filaments oriented by flow at the same protein concentration. The ratio of protein concentration in the I-band to that in the H-zone was determined by interferometry. The ratio of birefringence of the I-band to that of the H-zone per unit protein concentration was found to be about 0.9, which was comparable to the ratio of birefringence of the thin filaments and thick filaments in solution. The imbibition experiment showed that 70% of the total birefringence of the I-band is form birefringence and remaining 30% comes from intrinsic birefringence.

Animals↗
PubMed1972

Birefringence of spermatozoa. II. Form birefringence of bull sperm.

In thermal denaturation experiments on sperm cells, described in the accompanying paper, it was found that squid sperm, when melted, lose both birefringence and morphological shape. Bull sperm, on the other hand, show no change of morphology, but their initial negative birefringence becomes positive. Since this suggested the existence of form birefringence, the influence of solvents of different refractive indices on the observed birefringence was investigated, using a new derivation of the Wiener form birefringence equations which allows direct comparison of Wiener's theory with experimental results. Bull sperm showed form birefringence both before and after melting, while squid sperm showed none. Quantitative application of the general form of the Wiener equations to these results gave values for the refractive index and intrinsic birefringence of bull sperm cells. Application of the specific forms of the Wiener equations showed that neither of these descriptions of idealized systems was adequate to describe completely the form birefringence of bull sperm, but that the equation for platelike submicroscopic structures was more nearly an accurate fit to the data than that for rodlike structures.

Aniline Compounds↗
PubMed1985

Flow birefringence of microtubules and its relation to birefringence measurements in cells.

Understanding the molecular basis of mitotic movements in living cells will require correlative experiments on intact cells, cell models, purified tubulin, and perhaps other biopolymers. Birefringence is one assay that is useful in all of these experimental situations. Heretofore, studies of birefringence changes during mitosis have lacked a quantitative basis for interpretation in terms of microtubule number and packing density. One of the aims of this work was to establish that relationship. Purified calf brain tubulin was polymerized to equilibrium and oriented in the hydrodynamic field of a microcapillary flow birefringence apparatus. The relationship between birefringence and microtubule packing density was determined by a combination of optical, electron microscopic, and biochemical methods. The data correlate surprisingly well with those obtained by others from in vitro measurements on isolated mitotic spindles. Using the flow birefringence data, the sensitivity of polarizing microscopes for detecting microtubules was examined and found to depend on microtubule packing density, object thickness, and instrumental factors that limit both the detection and measurement of weakly birefringent objects. Because of the dependence of measurement sensitivity on object thickness, a method of measuring the thickness of microtubule bundles using the dispersion of birefringence was developed. This method is capable of measuring thickness to within two or three Airy diffraction units and does not require any assumptions regarding object symmetry.

Animals↗
PubMed2003

Compensation of the birefringence of a polymer by a birefringent crystal.

We report a method for compensating the birefringence of optical polymers by doping them with inorganic birefringent crystals. In this method, an inorganic birefringent material is chosen that has the opposite birefringence to that of the polymer and has rod-shaped crystals that are oriented when the polymer chains are oriented. The birefringence of the polymer is thus compensated by the opposing birefringence of the crystal. Birefringence is minimized in various polymer optical devices by adjusting process conditions, because it degrades the performance of devices. This method minimizes it, independent of process conditions, which potentially improves the productivity of devices.

Journal Article↗
PubMed1965

Intrinsic birefringence of poly-gamma-benzyl-L-glutamate, a helical polypeptide, and the theory of birefringence.

The intrinsic birefringence of macromolecules can be obtained directly from flow birefringence measurements in a solvent whose refractive index matches that of the solute. A small and positive value (approximately 0.01) was found for the helical polypeptide, poly-gamma-benzyl-L-glutamate. The birefringence in solvents of varying index calculated from the Peterlin-Stuart theory using this value of the intrinsic birefringence did not agree with experimental values. Considerations of polydispersity and shear deformation indicated that the discrepancy could not be attributed to these effects. Also it could not be explained in terms of specific solvent effects. It is concluded that optical properties cannot be derived from the continuum model employed by Peterlin and Stuart. Much better agreement was obtained with a helical dipole necklace model.

Birefringence↗
PubMed1972

Birefringence of spermatozoa. I. Birefringence melting of squid, bull, and human sperm nucleoprotein.

In experiments designed to determine the thermal stability and bonding strength of a natural nucleoprotein structure, the loss of birefringence as a function of time and temperature was investigated for both mammalian and nonmammalian sperm nuclei. At a constant temperature, this reaction was found to be first order for both types over a range of temperatures. The methods of chemical kinetics applied to results of these reactions, called birefringence melting reactions, produced values for the enthalpy and entropy of activation in the reactions, which gave some indication of the strength of binding in the nucleoprotein structure; and these results, plus those on the influence of chemicals on the structure, were consistent with the molecular structures which have been proposed by others for the nucleoprotein complex of sperm nuclei. For both bull and human sperm in ethylene glycol, the rate-limiting step in the melting reactions appeared to be the breakage of disulfide bonds. For squid sperm in ethylene glycol, and bull or squid sperm in ethylene glycol plus beta-mercaptoethanol, the identity of this step was more ambiguous, but a possibility consistent with these and other results would be a cooperative breakage of ionic bonds.

Animals↗
PubMed1976

Spindle birefringence of isolated mitotic apparatus: further evidence for two birefringent spindle components.

We studied sea-urchin zygote mitotic apparatus (MA) isolated in hexylene glycol, transferred immediately to a glycerol-dimethylsulphoxide medium, and stored for 2 weeks at room temperature. Treatment with 0-5 M KC1 caused loss of 45% of the birefringence, but microtubules remained intact (as seen electron microscopically in glutaraldehyde-fixed MA), and tubulin was not extracted (as determined by polyacrylamide gel electrophoresis). These results suggest that a non-tubulin component which is extracted by the KC1 contributes 45% of the MA birefringence. Further evidence for this conclusion came from indirect immunofluorescence experiments. Non-extracted (control) MA were fixed with formaldehyde and reacted with antibody against tubulin; there was intense staining of the spindle fibres and astral rays. Electron microscopically, however, microtubules were not present in formaldehyde-fixed MA. Since formaldehyde fixation caused breakdown of microtubules but the tubulin remained in the MA (as judged by reaction with antibodies) we suggest that after microtubule breakdown the tubulin remains in the MA because it is bound to a peri-microtubule spindle component (which we call 'substance gamma'). When KCl-extracted MA were fixed with formaldehyde and reacted with antibody against tubulin there was very little staining of spindle fibres and astral rays. Electron microscopically, formaldehyde caused microtubule breakdown, and since the tubulin is lost from formaldehydefixed, KC1-extracted MA (as judged by reaction with antibodies), we suggest that the tubulin-binding component, substance gamma, is extracted by the 0-5 M KC1. Pressure treatment caused the asters not to stain with antibody against tubulin, suggesting that the stability of substance gamma is different in different regions of the mitotic apparatus.

Animals↗
PubMed1993

Birefringence changes associated with isometric contraction and rapid shortening steps in frog skeletal muscle fibres.

1. Muscle birefringence, the difference between the refractive indices of light polarized parallel and perpendicular to the muscle fibre axis, was measured at 3 degrees C in intact single fibres isolated from frog muscle. Resting birefringence was 2.20 +/- 0.02 x 10(-3) (mean +/- S.E.M., n = 44) at sarcomere length 2.4-2.7 microns and 2.35 +/- 0.03 x 10(-3) (n = 19) at 3.5-3.8 microns. 2. Birefringence decreased during isometric twitch or tetanic contractions. The peak change in a twitch at sarcomere length 2.6 microns, determined by two independent methods, was 0.150 +/- 0.017 x 10(-3) (mean +/- S.E.M., n = 6). The corresponding value after 0.4 s of tetanic stimulation was 0.167 +/- 0.012 x 10(-3) (n = 6). 3. The birefringence change had a shorter latency than tension and reached its half-maximum value earlier than tension. The difference in time to half-maximum in tetani was 11.5 +/- 1.3 ms (mean +/- S.E.M., n = 6) at 3 degrees C. After stimulation birefringence recovered to its pre-stimulus baseline more slowly than tension. 4. The birefringence decrease after 0.4 s of tetanic stimulation was linearly related to the expected degree of overlap between actin and myosin filaments in the sarcomere length range 2.6-3.6 microns. The amplitude of the birefringence decrease at full filament overlap (sarcomere length 2.2 microns) was estimated to be 0.235 +/- 0.015 x 10(-3). 5. Birefringence changes associated with shortening steps of 0.9% fibre length at sarcomere length 2.6 microns exhibited four phases corresponding to those of the tension transient. There was no consistent birefringence change during the length step itself. During the rapid tension recovery birefringence increased by 0.014 +/- 0.001 x 10(-3) (n = 3), measured from the end of the length step to 2 ms later. Birefringence continued to increase as tension recovery slowed, reaching a peak about 10 ms after the step, then recovered with a rate similar to that of the final tension recovery. 6. These birefringence changes are likely to be caused by axial rotation of the head domain of the myosin cross-bridge. During isometric contraction heads bind to actin with their long axes more perpendicular to the fibre axis than in resting muscle, although there is likely to be a wide range of head orientations during contraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Action spectrum for changes in spindle fibre birefringence after ultraviolet microbeam irradiations of single chromosomal spindle fibres in crane-fly spermatocytes.

Single chromosomal spindle fibres in Nephrotoma suturalis (crane-fly) spermatocytes in metaphase and anaphase were irradiated with monochromatic ultraviolet light focussed to a 2 micrometer spot. In cells in both metaphase and anaphase either the birefringence of the irradiated spindle fibre was altered in the irradiated region, or there was no change, depending on the dose and wavelength of ultraviolet light used for the irradiation. When there was an area of reduced birefringence (ARB), it moved poleward regardless of whether the associated chromosome moved poleward. When cells were irradiated in early metaphase they remained in metaphase until the ARB reached the pole. In some cells irradiated in late metaphase the chromosomes began anaphase before the ARB reached the pole; in many such cells anaphase was abnormal in that all six half-bivalents separated at the start of anaphase but none moved polewards. In all cases the ARB moved poleward at the same speed as subsequent chromosome movement; that is, at about 0.8 micrometer/min. In cells irradiated in anaphase, spindle fibre birefringence was reduced independently of blockage of chromosome movement. Because birefringence and movement were altered independently there were four classes of results: (1) in some cases there was no effect on the movement of the chromosome associated with the irradiated spindle fibre and no effect on the birefringence of the irradiated spindle fibre. (2)In some cases, primarily with 260 nm wavelength light, there was no effect on the movement of the chromosome associated with the irradiated spindle fibre and there was an effect on the birefringence of the irradiated spindle fibre. (3) In some cases, primarily with 290 nm wavelength light, there was an effect on the movement of the chromosome associated with the irradiated spindle fibre and no effect on the birefringence of the irradiated spindle fibre. (4) In some cases, primarily with 270 nm and 280 nm wavelength light, there was an effect on the movement of the chromosomes associated with the irradiated spindle fibre and there was an effect on the birefringence of the irradiated spindle fibre. The action spectrum for reducing spindle fibre birefringence in crane-fly spermatocytes had two peaks, one at 260 nm and the other, less sensitive, at 280 nm. For irradiations at 270 nm, 280 nm and 290 nm, five to fifty times more energy was needed to reduce spindle fibre birefringence than to stop chromosome movement, but for irradiations at 260 nm five times less energy was needed to reduce spindle fibre birefringence than to stop chromosome movement. The action spectrum for reducing spindle fibre birefringence is quite different from that for stopping chromosome movement.

Anaphase↗
PubMed1991

Transient electric birefringence of two small DNA restriction fragments of the same molecular weight.

The transient electric birefringence of two small DNA restriction fragments of the same molecular weight, one of which migrates anomalously slowly on polyacrylamide gels, has been investigated. Both fragments exhibit negative birefringence. The decay of the birefringence of the anomalously slowly migrating fragment is 8-9% faster than that of the normally migrating fragment. The faster birefringence decay of the anomalous fragment 12A persists under a variety of buffer conditions, suggesting that it is due primarily to static bending and/or curvature of fragment 12A. In reversing electric fields the absolute amplitude of the birefringence of fragments 12A and 12B decreased about 26% before returning to the steady state value. The minimum in the birefringence occurred faster than expected from the birefringence decay times and decreased with increasing electric field strength, suggesting that the minimum is due to a slow polarization of the ion atmosphere. For both fragments, the rise of the birefringence in the Kerr region is about 10% slower than the field-free decay. The buildup of the negative birefringence is preceded either by an interval when no birefringence is observed or by a small positively birefringent transient, suggesting that a small transverse ionic polarizability is also present. Both DNA fragments exhibit Kerr law behavior over most of the range of electric field strengths investigated. Analysis of the shapes of the saturation curves suggests that differences may exist in the polarization mechanisms of the two fragments.

Base Sequence↗
PubMed1994

Transient electric birefringence of agarose gels. II. Reversing electric fields and comparison with other polymer gels.

The transient electric birefringence of low electroendosmosis (LE) agarose gels oriented by pulsed unidirectional electric fields was described in detail in Part I [J. Stellwagen and N. C. Stellwagen (1994), Biopolymers, Vol. 34, p. 187]. Here, the birefringence of LE agarose gels in rapidly reversing electric fields, similar in amplitude and duration to those used for field inversion gel electrophoresis, is reported. Symmetric reversing electric fields cause the sign of the birefringence of LE agarose gels, and hence the direction of orientation of the agarose fibers, to oscillate in phase with the applied electric field. Because of long-lasting memory effects, the alternating sign of the birefringence appears to be due to metastable changes in gel structure induced by the electric field. If the reversing field pulses are equal in amplitude but different in duration, the orientation behavior depends critically on the applied voltage. If E < 7 V/cm, the amplitude of the birefringence gradually decreases with increasing pulse number and becomes unmeasurably small. However, if E > 7 V/cm, the amplitude of the birefringence increases more than 10-fold after approximately 20 pulses have been applied to the gel, suggesting that a cooperative change in gel structure has occurred. Because there is no concomitant change in the relaxation times of the orienting particles, the large increase in the amplitude of the birefringence must be due to an increase in the number of agarose fibers and/or fiber bundles orienting in the electric field, which in turn indicates a cooperative breakdown of the noncovalent "junction zones" that cross-link the fibers into the gel matrix. The sign of the birefringence of LE agarose gels is always positive after extensive junction zone breakdown, indicating that the agarose fibers and fiber bundles preferentially orient parallel to the electric field when they are freed from the constraints of the gel matrix. Three other gel-forming polymers, high electroendosmosis (HEEO) agarose (a more highly charged agarose), beta-carrageenan (a stereoisomer of agarose), and polyacrylamide (a chemically cross-linked polymer) were also studied in unidirectional and rapidly reversing electric fields. The birefringence of HEEO agarose gels in reversing fields is very similar to that of LE agarose gels, suggesting that the orientation anomalies are not due to the occasional charged residues on the agarose backbone chain. The beta-carrageenan gels exhibit variable orientation behavior in reversing electric fields, suggesting that its internal gel structure is not as tightly interconnected as that of agarose gels.(ABSTRACT TRUNCATED AT 400 WORDS)

Birefringence↗
PubMed1988

Birefringence as a probe of crossbridge orientation in demembranated muscle fibres.

Birefringence measurements were used to investigate crossbridge orientation in demembranated muscle fibres of frog and rabbit. Birefringence depends on the interfilament spacing as well as on crossbridge orientation, so conditions were chosen such that changes in interfilament spacing were either eliminated or known from previous studies. At sarcomere length 2.3 micron there was a large birefringence decrease on putting relaxed fibres into rigor; at 3.7 micron this gave no change in birefringence. A simple model for crossbridge structure was used to interpret the birefringence data; it seems likely that reorientation of subfragment-1 (S-1) is responsible for the observed change. Decoration of rigor fibres with exogenous S-1 gave a birefringence increase corresponding to S-1 binding with its long axis at about 50 degrees to the fibre axis. The corresponding mean S-1 angle in relaxed muscle was estimated as about 35 degrees. When relaxation of rigor fibres was initiated by photolysis of caged-ATP in the absence of Ca2+ the birefringence increase showed two components, one 20 times faster than the other. The fast component was accompanied by a decrease of rapid stiffness, suggesting that it is caused by some crossbridges detaching to take up an orientation more parallel with the fibre axis. However the mechanical measurements indicated the presence of some active force generating crossbridges at this time, even in the absence of Ca2+, and these may also make a contribution to the fast birefringence component. Birefringence transients following ATP release in the presence of Ca2+ suggest that crossbridges are on average more perpendicular to the fibre axis during active force generation than in the rigor state.

Adenosine Triphosphate↗
PubMed1976

Birefringence of glycerinated crab muscle fiber under various conditions.

By using glycerinated single fibers of crab muscle (Sesarma haematocheir) which has long sarcomeres, the birefringence of the I band, H band and the overlapping region between thin and thick filaments was measured separately, under various environmental conditions. At the resting length, the birefringence of the fiber was decreased by the addition of Ca2+ in the absence of ATP, by about 0.35%. This birefringence decrease was found to take place in the overlapping region. The decrease corresponded to about 2% of the birefringence of thin filaments in this region. The birefringence of the fiber was increased by the addition of ATP in the absence of Ca2+, by about 6%. This birefringence increase also took place mostly in the overlapping region. The increase of birefringence by pyrophosphate was about half of that by ATP. The birefringence of the fiber was decreased by the increase of the ionic strength from 0.12 to 0.20. The origin of the observed changes of birefringence is discussed.

Adenosine Triphosphate↗
PubMed1965

LOCAL REDUCTION OF SPINDLE FIBER BIREFRINGENCE IN LIVING NEPHROTOMA SUTURALIS (LOEW) SPERMATOCYTES INDUCED BY ULTRAVIOLET MICROBEAM IRRADIATION.

Irradiation of the mitotic spindle in living Nephrotoma suturalis (Loew) spermatocytes with an ultraviolet microbeam of controlled dose produced a localized area of reduced birefringence in the spindle fibers. The birefringence was reduced only at the site irradiated, and only on the spindle fibers irradiated. Areas of reduced birefringence, whether produced during metaphase or during anaphase, immediately began to move toward the pole in the direction of the chromosomal fiber, even though the associated chromosomes did not necessarily move poleward. Both the poleward and the chromosomal sides of the area of reduced birefringence on each chromosomal fiber moved poleward with about the same, constant, velocity. On the average, the areas of reduced birefringence moved poleward with about the same velocities as did the chromosomes during anaphase. The area of reduced birefringence was interpreted as a region in which most, though not necessarily all, of the previously oriented material was disoriented by the irradiation. The poleward movement of the areas of reduced birefringence indicates that the spindle fibers are not static, nonchangeable structures. The poleward movement possibly represents the manner in which the birefringent spindle fibers normally become organized. All the experiments reported were on primary spermatocytes which completed the second meiotic division subsequent to the experimentation. Since both the irradiated and the control cells completed the two meiotic divisions, the movement and irradiation effects studied in the first division were nondegenerative.

Anaphase↗