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J S Wray

Publications and source records attributed to J S Wray.

12 recordsLinked to original sources
PubMed1993

The effect of lattice spacing change on cross-bridge kinetics in chemically skinned rabbit psoas muscle fibers. I. Proportionality between the lattice spacing and the fiber width.

Chemically skinned rabbit psoas muscle fibers/bundles were osmotically compressed with a macromolecule dextran T-500 (0-16%, g/100 ml) at 20 degrees C, 200 mM ionic strength, and pH 7.0. The lattice spacing of psoas bundles was measured by equatorial x-ray diffraction studies during relaxation and after rigor induction, and the results were compared with the fiber width measurements by optical microscopy. The purpose of the present study is to determine whether fiber width is a reliable measure of the lattice spacing, and to determine the available spacing for myosin cross-bridges between the thick and thin filaments. We observed that both the lattice spacing and the fiber width decreased with an increase in the dextran concentration during relaxation or after rigor induction, and that the spacing and the fiber width were proportionately related. We further observed that, in the absence of dextran, the lattice spacing (and the fiber width) shrank on a relax-to-rigor transition, whereas in the presence of 16% dextran, the spacing expanded on a relax-to-rigor transition. The cross-over of these plots occurred at the 4-7% dextran concentration. During Ca activation, the fiber width shrank in the absence of dextran, and it slightly expanded in the presence of 14.4% dextran. The degree of expansion was not as large as in the relax-to-rigor transition, and the cross-over occurred at about 11% dextran concentration. We also carried out experiments with dextran T-40 and T-10 to determine the upper limit of the molecular weight that enters the lattice space. We found that the upper limit is about 20 kD.

Actins↗
PubMed1990

Effect of ionic strength on crossbridge kinetics as studied by sinusoidal analysis, ATP hydrolysis rate and X-ray diffraction techniques in chemically skinned rabbit psoas fibres.

In order to identify which steps in the crossbridge are affected by changes in ionic strength, we studied the effect of ionic strength on the rate constants and magnitudes of three exponential processes, the ATP hydrolysis rate and isometric tension during maximal activation (pCa 4.52, 5 mM MgATP). Equatorial X-ray diffraction measurements were also carried out in both relaxing and rigor conditions to examine whether the distance between thick and thin filaments changes with ionic strength (range: 100-300 mM). All experiments were carried out at 20 degrees C and at pH 7.0 on chemically skinned rabbit psoas muscle fibres. Isometric tension and muscle stiffness declined significantly as the ionic strength was increased from 150 mM to 300 mM. The concomitant decrease in the ATP hydrolysis rate was much less than tension, resulting in a large increase in the tension cost. Three rate constants of exponential processes, deduced from sinusoidal analysis, did not change appreciably. The magnitude parameters of all three processes diminished as the ionic strength was increased. During relaxation the filament spacing increased by 5% when the ionic strength was increased from 150 mM to 300 mM. After rigor induction, the spacing did not change with ionic strength. We conclude that a change in ionic strength modifies the rapid equilibrium between the detached state and the 'weakly attached' state, and that this causes considerable effect on isometric tension. We also conclude that other steps in the crossbridge cycle are less sensitive to ionic strength, and that the lattice spacing change is unable to account for the considerable effect of ionic strength on isometric tension.

Adenosine Triphosphate↗
PubMed1988

Towards a molecular mechanism for the crossbridge cycle.

Present evidence on crossbridge behaviour is reviewed from the viewpoint of the Eisenberg-Hill concepts. We conclude that a cartoon illustrating the operation of these ideas in practice should be drawn so as to include morphological changes in the body of the myosin molecule as part of the power-stroke. The bulk of structural evidence on the operation of crossbridges in intact muscle supports such a description.

Animals↗
PubMed1986

ATP binding and crossbridge structure in muscle.

Thick filaments extracted from insect flight muscle were used in examining whether the dependence of actin-myosin crossbridge structure on nucleotide, generally presumed to underlie the power-stroke, is exhibited by myosin alone. The strongly periodic crossbridge arrangement seen in the presence of ATP (corresponding to relaxed muscle) is reversibly lost in conditions that induce rigor in intact muscle fibres. These observations suggest that the power-stroke may involve changes in the steric relation of the myosin head to the thick as well as to the thin filament.

Actin Cytoskeleton↗
PubMed1984

Cross-bridge states in invertebrate muscles.

Arguments are presented for doubting whether the effect of AMPPNP on insect flight muscle in rigor signals a reversion of the power stroke of attached cross-bridges. Instead, the effect of this nucleotide on insect and other muscles may be better explained in terms of the behavior of detached bridges. Knowledge of events in the detached half of the contractile cycle may nevertheless be relevant to understanding the mechanism of energy transduction.

Adenosine Triphosphate↗
PubMed1979

Structure of the backbone in myosin filaments of muscle.

New X-ray data suggest how myosin rods, themselves alpha-helical coiled coils, form the thick filament backbone of crustacean muscles by additional supercoiling. Natural transformations of this structure may describe the myosin backbone in many other animals also.

Animals↗
PubMed1975

Diversity of cross-bridge configurations in invertebrate muscles.

X-ray diffraction patterns from relaxed invertebrate muscles reveal the thick filament symmetries and cross-bridge configurations. The cross bridges are substantially angled to the filament axes. The results on symmetry are generally consistent with Squire's model.

Actins↗