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  • 1
    Electronic Resource
    Electronic Resource
    Characterization of a novel pectate lyase, Pel10A, from Pseudomonas cellulosa (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1141-1143 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Biological recycling of plant material is essential for biosphere maintenance. This perpetual task involves a complex array of enzymes, including extracellular polysaccharide hydrolases and lyases. Whilst much is known about the structure and function of the hydrolases, relatively little is known about the structures and mechanisms of the corresponding lyases. To this end, crystals of the catalytic module of a novel family 10 pectate lyase, Pel10A from Pseudomonas cellulosa, were obtained using polyethylene glycol 2000 monomethylether as a precipitant. They belong to space group P21, with unit-cell parameters a = 47.7, b = 106.1, c = 55.4 Å, β = 92.0°, and have two molecules in the asymmetric unit. The crystals diffract beyond 1.5 Å using synchrotron radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444901007491
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  • 2
    Electronic Resource
    Electronic Resource
    Measured and modeled properties of mammalian skeletal muscle: IV. Dynamics of activation and deactivation (2000)
    Springer
    Journal of muscle research and cell motility 21 (2000), S. 33-47 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The interactive effects of length and stimulus frequency on rise and fall times and on sag were investigated in fast-twitch feline caudofemoralis at normal body temperature. The length and stimulus frequency ranges studied were 0.8–1.2 L 0 and 15–60 pps. Isometric rise times were shortest under two sets of conditions: short lengths + low stimulus frequencies and long lengths + high stimulus frequencies. In contrast the isometric fall time relationship showed a single minimum at short lengths + low stimulus frequencies. Velocity was shown to have an additional effect on fall time, but only at higher stimulus frequencies (40–60 pps): fall times were shorter during movement in either direction as compared to isometric. The effects of sag were greatest at shorter lengths and lower stimulus frequencies during isometric stimulus trains. Potential mechanisms underlying this last effect were investigated by comparing isometric twitches elicited prior to and immediately following a sag-inducing stimulus train. Post-sag twitches produced less force, reached peak force earlier and initially decayed more quickly compared to pre-sag twitches. However, the final rate of force decay and the initial rate of force rise (during the first 15 ms) were unaffected by sag. We construct a logical argument based on these findings to hypothesize that the predominant mechanism underlying sag is an increase in the rate of sarcoplasmic calcium ion removal. All of the above findings were used to construct a model of activation dynamics for fast-twitch muscle, which was then extrapolated to slow-twitch muscle. When coupled with a previous model of kinematic dynamics, the complete model produced accurate predictions of the forces actually recorded during experiments in which we applied concurrent dynamic changes in length, velocity and stimulus frequency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005687416896
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanics of feline soleus: I. Effect of fascicle length and velocity on force output (1996)
    Springer
    Journal of muscle research and cell motility 17 (1996), S. 207-219 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The aim of the present study was to quantify how fascicle length and velocity modify force production in cat soleus. A computerized muscle puller controlled the length and velocity of the whole-muscle. We recorded the force output at the tendon and the length of muscle fascicles using sonomicrometry during whole-muscle isometric and isokinetic contractions. Peak muscle stress was estimated as 31.8±4.1 N cm-2 (mean and sd) and optimal fascicle length, L0, was estimated as 3.8±0.6 cm which corresponds to an optimal sarcomere length of 2.49±0.08 μm. The isometric force-length data followed closely the expected force-length relationship for cat sarcomeres. The force-velocity relationship was found to be similar in shape between cats, but the per cent increment of force over isometric levels for lengthening contractions was highly variable. Estimates of the kinematics of the fascicles based on whole-muscle length were systematically incorrect; whole-muscle velocity was 21% greater than fascicle velocity. The force-velocity data demonstrated consistent dependencies on fascicle length. At lengths below 0.7 L0 (1.74 μm), the shape of the force-velocity relationship was altered by the inclusion of a passive, repulsive force in the estimate of active isometric force. The shape of the force-velocity relationship changed at lengths greater than 0.7 L0, but was restricted to lengthening velocities where the increment of force with respect to isometric levels was found to increase with fascicle length. This change in shape in the force-velocity relationship for lengthening contractions reveals a systematic, but previously unknown interdependence between fascicle length and velocity on muscle force production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00124243
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  • 4
    Electronic Resource
    Electronic Resource
    Measured and modeled properties of mammalian skeletal muscle. I. The effects of post-activation potentiation on the time course and velocity dependencies of force production (1999)
    Springer
    Journal of muscle research and cell motility 20 (1999), S. 443-456 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Activation of mammalian fast-twitch skeletal muscle induces a persistent effect known as post-activation potentiation (PAP), classically defined as an increase in force production at sub-maximal levels of activation. The underlying mechanism is thought to be phosphorylation of the myosin regulatory light chain (MRLC), which leads to an increase in the rate constant for cross-bridge attachment (Sweeney et al., 1993). If true, this suggests the hypothesis that other contractile properties should be affected during PAP. Using a feline fast-twitch whole-muscle preparation (caudofemoralis) at 37∘C, we observed that PAP greatly increased tetanic forces during active lengthening, decreased isometric tetanic rise times and delayed isometric tetanic force relaxation. The first two of these effects were length dependent with a greater effect occurring at shorter lengths. These findings confirmed that PAP has other functionally important effects beyond a simple increase in sub-maximal isometric forces. Furthermore, length was found to have an effect independent of PAP on the shortening half of the FV relationship (less force was produced at longer lengths) and on the rate of force relaxation during the later stages of isometric tetanic force decay (slower relaxation at longer lengths). All of these findings can be explained with a simplified, two-state model of cross-bridge dynamics that accounts for the interaction of both interfilament spacing and MRLC phosphorylation on the apparent rate constants for cross-bridge attachment and detachment. These findings are largely consistent with data collected previously from reduced preparations such as skinned fibers at cold, unphysiological temperatures (e.g. 5∘C). One finding that could not be explained by our model was that twitch fall times in the dispotentiated state were parabolically correlated with length, whereas in the potentiated state the relationship was linear. The time course of decay of this effect did not follow the time course of force dispotentiation, suggesting that there are other activation-dependent processes occurring in parallel with MRLC phosphorylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005590901220
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanics of feline soleus: II design and validation of a mathematical model (1996)
    Springer
    Journal of muscle research and cell motility 17 (1996), S. 221-233 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have developed a mathematical model to describe force production in cat soleus during steady-state activation over a range of fascicle lengths and velocities. The model was based primarily upon a three element design by Zajac but also considered the many different features present in other previously described models. We compared quantitatively the usefulness of these features and putative relationships to account for a set of force and length data from cat soleus whole-muscle described in a companion paper. Among the novel features that proved useful were the inclusion of a short-length passive force resisting compression, a new normalisation constant for connective-tissue lengths to replace the potentially troublesome slack length, and a new length dependent term for lengthening velocities in the force-velocity relationship. Each feature of this model was chosen to provide the most accurate description of the data possible without adding unneeded complexity. Previously described functions were compared with novel functions to determine the best description of the experimental data for each of the elements in the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00124244
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of sarcomere length on triad locationin intact feline caudofemoralis muscle fibres (1998)
    Springer
    Journal of muscle research and cell motility 19 (1998), S. 473-477 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The location of triads within a mammalian skeletal muscle sarcomere has traditionally been defined as ‘at the A-I junction’. We attempted to verify this statement by examining systematically the location of triads within the sarcomere over the physiological range of sarcomere lengths. This study was conducted using intact feline muscle fibres from caudofemoralis – an exclusively fast-twitch muscle from the hindlimb. Our results in intact fibres indicate that the distance between the Z-band and triad (ZT) is relatively constant over the range of sarcomere lengths (SLs) examined in this study (1.8–3.4μm). The slope between ZT and SL was measured to be 0.06 ± 0.01 (r=0.36, p 〈 0.001) while the slope between the M-line to triad distance (MT) and SL was measured to be 0.440.01 (r 〉 0.9, p 〈 0.001). The mean ZT was 0.52 ± 0.07μm, which corresponds to a triad location approximately halfway along the thin filaments. These results do not support the traditional statement regarding triad location. Nor do these results support a similar recent study conducted using chemically skinned muscle fibres from rat extensor digitorum longus (also a homogeneously fast-twitch muscle of the hindlimb), in which a slope of 0.25 was observed between ZT and SL (r 〉 0.9, p 〈 0.01). These results are, however, in qualitative agreement with results using intact fibres from fast-twitch rat semitendinosus. Based upon known morphology, we suggest that the only structure supporting triad position is the SR itself, and that a non-homogeneous distribution of the SR within the sarcomere might be responsible for maintaining triad location near the mid-region of the thin filaments. We also suggest that there might be optimal design reasons for locating the triads at the mid-region of the thin filaments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005309107903
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  • 7
    Electronic Resource
    Electronic Resource
    Measured and modeled properties of mammalian skeletal muscle. II. The effectsof stimulus frequency on force-length and force-velocity relationships (1999)
    Springer
    Journal of muscle research and cell motility 20 (1999), S. 627-643 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Interactions between physiological stimulus frequencies, fascicle lengths and velocities were analyzed in feline caudofemoralis (CF), a hindlimb skeletal muscle composed exclusively of fast-twitch fibers. Split ventral roots were stimulated asynchronously to produce smooth contractions at sub-tetanic stimulus frequencies. As described previously, the peak of the sub-tetanic force-length relationship was found to shift to longer lengths with decreases in stimulus frequency, indicating a length dependence for activation that is independent of filament overlap. The sub-tetanic force-velocity (FV) relationship was affected strongly both by stimulus frequency and by length; decreases in either decreased the slope of the FV relationship around isometric. The shapes of the force transients following stretch or shortening revealed that these effects were not due to a change in the instantaneous FV relationship; the relative shape of the force transients following stretch or shortening was independent of stimulus frequency and hardly affected by length. The effects of stimulus frequency and length on the sub-tetanic FV relationship instead appear to be caused by a time delay in the length-dependent changes of activation. In contrast to feline soleus muscle, which is composed exclusively of slow-twitch fibers, CF did not yield at sub-tetanic stimulus frequencies for the range of stretch velocities tested (up to 2 L0/s). The data presented here were used to build a model of muscle that accounted well for all of the effects described. We extended our model to account for slow-twitch muscle by comparing our fast-twitch model with previously published data and then changing the necessary parameters to fit the data. Our slow-twitch model accounts well for all previous findings including that of yielding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005585030764
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  • 8
    Electronic Resource
    Electronic Resource
    Measured and modeled properties of mammalian skeletal muscle: III. the effects of stimulus frequency on stretch-induced force enhancement and shortening-induced force depression (2000)
    Springer
    Journal of muscle research and cell motility 21 (2000), S. 21-31 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Stretch-induced force enhancement and shortening-induced force depression were examined in fast-twitch feline caudofemoralis muscle at 37∘C. These phenomena were induced by applying ramp length changes during the first 100–200 ms of an otherwise isometric contraction. The effects of various stimulus frequencies ranging from 30 to 120 pps were investigated over lengths ranging from 0.85 to 1.15 L 0. Distributed asynchronous stimulation of bundles of ventral roots was employed to produce smooth contractions at sub-tetanic stimulus frequencies in whole muscle. Of the two components of force enhancement identified by Noble (1992) we observed only the transient component that decays with time; we did not observe residual force enhancement. The force depression that we observed was symmetrical in almost all respects to the transient force enhancement, and was unlike the shortening-induced de-activation and residual force depression identified by Edman (Edman, 1975; Edman et al., 1993). Both transient force enhancement and depression were independent of work, load and activation. Reversals in the direction of ramp length changes following either an initial stretch or initial shortening were shown to cancel the effects of both transient force enhancement and transient force depression. The distances over which these cancellations could be achieved were different for the lengthening and shortening effects. This asymmetry can be reconciled with the predictions of Huxley's original cross-bridge mechanism by incorporating the recent suggestion that myosin heads can interact with multiple actin binding sites during a single ‘working’ stroke. We conclude that the types of force enhancement/depression that are most likely to be encountered under physiological conditions are the transient effects observed here, but that even these will have relatively little effect on force production during most natural behaviors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005619014170
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  • 9
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    Unknown
    Directional motor control (1996)
    Cell Press
    Details
    Publication Date: 1996-04-01
    Print ISSN: 0166-2236
    Electronic ISSN: 1878-108X
    Topics: Biology , Medicine
    Published by Cell Press
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  • 10
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    Unknown
    Characterization of a novel pectate lyase, Pel10A, fromPseudomonas cellulosa (2001)
    International Union of Crystallography
    Details
    Publication Date: 2001-07-23
    Print ISSN: 0907-4449
    Electronic ISSN: 1399-0047
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by International Union of Crystallography
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