Does phosphate release limit the ATPases of soleus myofibrils? Evidence that (A)M· ADP·Pi states predominate on the cross-bridge cycle

Iorga, Bogdan; Candau, Robin; Travers, Franck; Barman, Tom; Lionne, Corinne

doi:10.1007/s10974-004-0812-2

Cited by 7 publications

(10 citation statements)

References 49 publications

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“…Second, A is determined more accurately in relaxed than in activated conditions, because the steady state is slower. Third, with myofibrils, A is similar to the amplitude of titration experiments (cold ATP chase), because the equilibrium constant of the cleavage step is large (23,27).…”

Section: Methodsmentioning

confidence: 85%

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Paradoxical effects of endurance training and chronic hypoxia on myofibrillar ATPase activity

Roels¹,

Reggiani²,

Reboul³

et al. 2008

American Journal of Physiology-Regulatory, Integrative and Comp

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This study aimed to determine the changes in soleus myofibrillar ATPase (m-ATPase) activity and myosin heavy chain (MHC) isoform expression after endurance training and/or chronic hypoxic exposure. Dark Agouti rats were randomly divided into four groups: control, normoxic sedentary (N; n = 14), normoxic endurance trained (NT; n = 14), hypoxic sedentary (H; n = 10), and hypoxic endurance trained (HT; n = 14). Rats lived and trained in normoxia at 760 mmHg (N and NT) or hypobaric hypoxia at 550 mmHg (approximately 2,800 m) (H and HT). m-ATPase activity was measured by rapid flow quench technique; myosin subunits were analyzed with mono- and two-dimensional gel electrophoresis. Endurance training significantly increased m-ATPase (P < 0.01), although an increase in MHC-I content occurred (P < 0.01). In spite of slow-to-fast transitions in MHC isoform distribution in chronic hypoxia (P < 0.05) no increase in m-ATPase was observed. The rate constants of m-ATPase were 0.0350 +/- 0.0023 s(-1) and 0.047 +/- 0.0050 s(-1) for N and NT and 0.033 +/- 0.0021 s(-1) and 0.038 +/- 0.0032 s(-1) for H and HT. Thus, dissociation between variations in m-ATPase and changes in MHC isoform expression was observed. Changes in fraction of active myosin heads, in myosin light chain isoform (MLC) distribution or in MLC phosphorylation, could not explain the variations in m-ATPase. Myosin posttranslational modifications or changes in other myofibrillar proteins may therefore be responsible for the observed variations in m-ATPase activity.

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Section: Methodsmentioning

confidence: 85%

“…From these latter soleus muscles, myofi-brils were prepared as previously described (11). The total myosin head concentration in the myofibrillar suspension was measured by absorption at 280 nm of a 1/20 dilution of the suspension in 2% SDS (23). Sarcomere length of the myofibrils was measured as previously described (11).…”

Section: Methodsmentioning

confidence: 99%

Paradoxical effects of endurance training and chronic hypoxia on myofibrillar ATPase activity

Roels¹,

Reggiani²,

Reboul³

et al. 2008

American Journal of Physiology-Regulatory, Integrative and Comp

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“…The fast muscle myosin S1 from the rabbit (mixed MHC-2 isoforms) has been thoroughly investigated but the biochemical kinetics of the rabbit slow isoform (MHC-1) have not been reported in detail. Iorga et al (37) have compared the kinetics of ATP binding and hydrolysis by rabbit soleus and psoas myofibrils. The amino acid sequence for MHC-1 of mammals is ϳ80% identical to MHC-2 within the motor domain and for a discussion of the structural and functional differences between MHC-1 and MHC-2 see Ref.…”

Section: Discussionmentioning

confidence: 99%

The Slow Skeletal Muscle Isoform of Myosin Shows Kinetic Features Common to Smooth and Non-muscle Myosins

Iorga

Adamek

Geeves

2007

Journal of Biological Chemistry

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Fast and slow mammalian muscle myosins differ in the heavy chain sequences (MHC-2, MHC-1) and muscles expressing the two isoforms contract at markedly different velocities. One role of slow skeletal muscles is to maintain posture with low ATP turnover, and MHC-1 expressed in these muscles is identical to heavy chain of the ␤-myosin of cardiac muscle. Few studies have addressed the biochemical kinetic properties of the slow MHC-1 isoform. We report here a detailed analysis of the MHC-1 isoform of the rabbit compared with MHC-2 and focus on the mechanism of ADP release. We show that MHC-1, like some non-muscle myosins, shows a biphasic dissociation of actin-myosin by ATP. Most of the actinmyosin dissociates at up to ϳ1000 s ؊1, a very similar rate constant to MHC-2, but 10 -15% of the complex must go through a slow isomerization (ϳ20 s ؊1 ) before ATP can dissociate it. Similar slow isomerizations were seen in the displacement of ADP from actinmyosin⅐ADP and provide evidence of three closely related actinmyosin⅐ADP complexes, a complex in rapid equilibrium with free ADP, a complex from which ADP is released at the rate required to define the maximum shortening velocity of slow muscle fibers (ϳ20 s ؊1 ), and a third complex that releases ADP too slowly (ϳ6 s ؊1 ) to be on the main ATPase pathway. The role of these actin-myosin⅐ADP complexes in the mechanochemistry of slow muscle contraction is discussed in relation to the load dependence of ADP release.Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes (1-6). During the myosin ATPase cycle, the myosin motor domain (or cross-bridge) undergoes a series of conformational changes coupled to the binding of nucleotide and actin, which results in a translocation of the myosin cargo domain relative to the actin track (7). The sequence of molecular events in the actin-myosin cross-bridge cycle appears essentially the same for all myosins so far studied. The different mechanochemical properties of each myosin are attributed to a modulation of the rates and equilibrium constants of individual molecular events to match each myosin to its physiological role.The most widely studied myosins are the vertebrate, striatedmuscle myosins, which define the class II myosins. This class of myosins have a dimerization domain that forms a long coiled-coil and which can assemble further to form the backbone of the bipolar thick myosin filament. Of the class II myosin, the myosin heavy chain 2 (MHC-2) 4 isoform found primarily in white, anaerobic, fast-contracting, skeletal muscle has been most thoroughly described at both the molecular and physiological levels. In adult, mammalian, muscle tissue the MHC-2 is found as various isoforms (e.g. 2a, 2b, 2x) and it has been established that the essential mechanical properties of the muscle fiber contraction (e.g. maximum velocity of shortening, force per cross-bridge) are properties of the MHC present in the t...

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“…The introduction of a phosphate-binding protein assay [19] enables investigators to directly probe the kinetics of P i release from Ca 2+ -activated myofibrils [7,64,89,91,92] and leads to straightforward conclusions about chemical states. The P i transient induced by mixing myofibrils with ATP exhibits a lag when myofibrils shorten in the absence of external load; thus, during active unloaded shortening, most cross-bridges are in ADP·P i states [89].…”

Section: Troponin Regulatory Kineticsmentioning

confidence: 99%

“…Two techniques have been used to rapidly change the concentration of compounds in myofibrils: (1) rapid mixing of myofibril suspensions with buffers in a reaction chamber by stopped flow or quench flow to study the transient kinetics of myofibril ATPase and myofibril Ca 2+ regulation [7,8,58,64,88,92,98,132,134] and (2) rapid switching between two laminar flows of solution ejected by a double-channel micropipette to induce force kinetics and sarcomere dynamics in single myofibrils mounted in a force-recording apparatus [26]. The principle of this technique is illustrated in Fig.…”

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confidence: 99%

Insights into the kinetics of Ca2+-regulated contraction and relaxation from myofibril studies

Stehle

Solzin

Iorga

et al. 2009

Pflugers Arch - Eur J Physiol

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Muscle contraction results from force-generating interactions between myosin cross-bridges on the thick filament and actin on the thin filament. The force-generating interactions are regulated by Ca(2+) via specialised proteins of the thin filament. It is controversial how the contractile and regulatory systems dynamically interact to determine the time course of muscle contraction and relaxation. Whereas kinetics of Ca(2+)-induced thin-filament regulation is often investigated with isolated proteins, force kinetics is usually studied in muscle fibres. The gap between studies on isolated proteins and structured fibres is now bridged by recent techniques that analyse the chemical and mechanical kinetics of small components of a muscle fibre, subcellular myofibrils isolated from skeletal and cardiac muscle. Formed of serially arranged repeating units called sarcomeres, myofibrils have a complete fully structured ensemble of contractile and Ca(2+) regulatory proteins. The small diameter of myofibrils (few micrometres) facilitates analysis of the kinetics of sarcomere contraction and relaxation induced by rapid changes of [ATP] or [Ca(2+)]. Among the processes studied on myofibrils are: (1) the Ca(2+)-regulated switch on/off of the troponin complex, (2) the chemical steps in the cross-bridge adenosine triphosphatase cycle, (3) the mechanics of force generation and (4) the length dynamics of individual sarcomeres. These studies give new insights into the kinetics of thin-filament regulation and of cross-bridge turnover, how cross-bridges transform chemical energy into mechanical work, and suggest that the cross-bridge ensembles of each half-sarcomere cooperate with each other across the half-sarcomere borders. Additionally, we now have a better understanding of muscle relaxation and its impairment in certain muscle diseases.

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Does phosphate release limit the ATPases of soleus myofibrils? Evidence that (A)M· ADP·Pi states predominate on the cross-bridge cycle

Cited by 7 publications

References 49 publications

Paradoxical effects of endurance training and chronic hypoxia on myofibrillar ATPase activity

Paradoxical effects of endurance training and chronic hypoxia on myofibrillar ATPase activity

The Slow Skeletal Muscle Isoform of Myosin Shows Kinetic Features Common to Smooth and Non-muscle Myosins

Insights into the kinetics of Ca2+-regulated contraction and relaxation from myofibril studies

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