Kinetics and regulation of the myofibrillar adenosine triphosphatase

Goodno, Charles C.; Wall, C M; Perry, S. V.

doi:10.1042/bj1750813

Cited by 42 publications

(11 citation statements)

References 31 publications

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“…The source of the increased base-line tension at low ionic strength was not determined. In this regard, Goodno, Wall & Perry (1978) found that the ATPase activity of relaxed myofibrils increased as the ionic strength was reduced below physiological levels. This suggests that the increase in resting tension at an ionic strength of 0 09 M may result from cyclic interactions of cross-bridges with actin sites.…”

Section: Resultsmentioning

confidence: 98%

Effects of calcium and ionic strength on shortening velocity and tension development in frog skinned muscle fibres.

Julian¹,

Moss²

1981

The Journal of Physiology

113

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SUMMARY1. The influence of Ca2+ concentration and ionic strength on the maximum velocity of shortening (Vmax) and the tension generating capability of frog skinned muscle fibres has been studied at temperatures between 1 and 101C.2. Fibre segments were mounted between a force transducer and servo motor, where they could be viewed and photographed through a microscope. Segments in which the striations became non-uniform during activation were discarded.3. Velocity was obtained as a function of load by stepping the tension to values less than the steady isometric tension. Vmax was then determined by an extrapolation technique. Vmax was also obtained using a second, independent method by measuring the times required to take up various amounts of slack imposed on the segments. 4. Vmax was significantly influenced by the Ca2+ concentration, decreasing by about one half when the Ca2+ concentration was reduced to give steady tensions less than half-maximal. 5. Vma. was not influenced by changes in ionic strength, in the range 0-09-018 M.Steady tension was found to increase as ionic strength was decreased in the same range.6. These results indicate that the effect of changes in ionic strength is to alter the numbers or stiffness of attached cross-bridges, while there is no apparent influence of ionic strength on the steady-state kinetics of the actin-myosin interaction during unloaded shortening. The mechanism responsible for the influence of Ca2+ on Vmax is unknown, though possible sites of action for Ca2+ are discussed.

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Section: Resultsmentioning

confidence: 98%

Effects of calcium and ionic strength on shortening velocity and tension development in frog skinned muscle fibres.

Julian¹,

Moss²

1981

The Journal of Physiology

113

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“…3) in reversible association with actin also increases (Stein et al, 1979) . Because k2 includes the refractory state transition, which is believed to be rate limiting in isolated protein systems (Eisenberg and Greene, 1980), and because the rate of hydrolysis increases in myofibrils with a decrease in ionic strength (over the range 0.1-0.2; Goodno et al, 1978), we argue that reduction in ionic strength decreases the lifetime of the refractory state, i.e., increases k2 . This will produce the effects we observe (Table II) : a left shift in the pCa/tension curve (Eq.…”

Section: Discussionmentioning

confidence: 99%

“…When ionic strength is reduced, the hydrolysis rate of myofibrils increases (Goodno et al ., 1978) . The fraction of myosin products (X in Eq.…”

Section: Discussionmentioning

confidence: 99%

Effect of cross-bridge kinetics on apparent Ca2+ sensitivity.

Brandt¹,

Cox²,

Kawai³

et al. 1982

The Journal of General Physiology

148

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Three different ways of shifting the pCa/tension curve on the pCa axis have been studied and related to changes in the rate constants of the crossbridge cycle. The curve midpoint shifts to higher pCa's wheel the substrate (Mg-ATP) is reduced from 5 to 0.25 mM, when the phosphate concentration is reduced from 7.5 mM to 0, and when the ionic strength is reduced from 0.200 to 0.120 . The Hill coefficients of the pCa/tension curve in our standard saline (5 mM substrate, 5 mM free ATP, 7.5 mM phosphate, ionic strength 0.200, 15°C) are between 5.1 and 5.6 and fall to 3.0 with the left shift of the curve brought about by reducing both substrate and phosphate. Left shifts of the curve produced by reduction in the ionic strength do not result in a lower Hill coefficient . Reducing either substrate or phosphate is associated with a reduction in the optimal frequency for oscillatory work, but reduction in ionic strength is not so associated . Maximum tension increases with the left shift of the curve brought about by reducing phosphate concentration or ionic strength, but tension decreases with the left shift of the curve accompanying substrate concentration reduction in a phosphate-free saline . We argue that one mechanism for the observed shift of the curve along the pCa axis is the relationship between the time a cross-bridge takes to complete a cycle and the time Ca 2+ stays bound to troponin C (TnC) . If the cycle rate is decreased, a smaller fraction of TnC sites must be occupied to keep a given fraction of cross-bridges active . To illustrate this concept, we present a simplified model of the cross-bridge cycle incorporating the kinetics of Ca binding to TnC.

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“…ES is myosin ATPase, and the low rate of ATP formation gives a plausible first order kinetic for this enzyme. The first order kinetic constant kz = V$TPase/K~Tpase may be estimated to be 0.09 min-' for the myofilaments used in fig.2 (eTPase = 1.3 pM.min-'* KiTPase = 14pM [13]). v/a = 10 cm (v = 2 m;, volume of the spec- Fig.3.…”

Section: Creatine Kinase Activitymentioning

confidence: 99%

An example of substrate channeling between co‐immobilized enzymes Coupled activity of myosin ATPase and creatine kinase bound to frog heart myofilaments

Arrio-Dupont

1988

FEBS Letters

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In myofilaments obtained by Triton X-100 lysis of frog heart cells in high ionic strength medium, the activity of bound creatine kinase cannot be detected by a coupled enzymatic assay. ATP is channel&d toward myosin ATPase, through the unstirred layer near myofilaments and cannot diffuse into the bulk solution. Model systems based upon the coupled kinetics of enzymes co-immobilized on the same surface may explain this behaviour. This may also account for why myofilament-bound creatine kinase is more efficient than free enzyme in the cytosol for the physiological recycling of ADP into ATP.

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Kinetics and regulation of the myofibrillar adenosine triphosphatase

Cited by 42 publications

References 31 publications

Effects of calcium and ionic strength on shortening velocity and tension development in frog skinned muscle fibres.

Effects of calcium and ionic strength on shortening velocity and tension development in frog skinned muscle fibres.

Effect of cross-bridge kinetics on apparent Ca2+ sensitivity.

An example of substrate channeling between co‐immobilized enzymes Coupled activity of myosin ATPase and creatine kinase bound to frog heart myofilaments

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