Rate of Phosphate Release after Photoliberation of Adenosine 5′-Triphosphate in Slow and Fast Skeletal Muscle Fibers

He, Z.-H.; Stienen, G. J. M.; Barends, J. P. F.; Ferenczi, Michael A.

doi:10.1016/s0006-3495(98)77683-0

Cited by 26 publications

(49 citation statements)

References 51 publications

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“…Caged isoprenoid diphosphates 5 and 9 meet these criteria. In addition, their uncaging kinetics are comparable with many other commercially available and previously reported caged enzyme substrates/inhibitors and signaling molecules (see Table 1) (47–52). Caged ATP (molecular probes) has been widely used to study the mechanism of ATPases (49,50) and the molecular basis of skeletal muscle fiber contraction (48,52).…”

Section: Discussionsupporting

confidence: 78%

Caged Protein Prenyltransferase Substrates: Tools for Understanding Protein Prenylation

DeGraw

Hast

et al. 2008

Chem Biol Drug Des

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Originally designed to block the prenylation of oncogenic Ras, inhibitors of protein farnesyltransferase currently in pre-clinical and clinical trials are showing efficacy in cancers with normal Ras. Blocking protein prenylation has also shown promise in the treatment of malaria, Chagas disease, and progeria syndrome. A better understanding of the mechanism, targets and in vivo consequences of protein prenylation are needed to elucidate the mode of action of current PFTase inhibitors and to create more potent and selective compounds. Caged enzyme substrates are useful tools for understanding enzyme mechanism and biological function. Reported here is the synthesis and characterization of caged substrates of PFTase. The caged isoprenoid diphosphates are poor substrates prior to photolysis. The caged CAAX peptide is a true catalytically caged substrate of PFTase in that it is to not a substrate, yet is able to bind to the enzyme as established by inhibition studies and x-ray crystallography. Irradiation of the caged molecules with 350 nm light readily releases their cognate substrate, and their photolysis products are benign. These properties highlight the utility of those analogues towards a variety of in vitro and in vivo applications.

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Section: Discussionsupporting

confidence: 78%

Caged Protein Prenyltransferase Substrates: Tools for Understanding Protein Prenylation

DeGraw

Hast

et al. 2008

Chem Biol Drug Des

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“…If we assume that at 35% of maximal isometric force only 35% of the cross bridges are functioning and a myosin subfragment I concentration of 150 M (7), then ATP splitting per cross bridge would amount to 65, 34, and 21 s Ϫ1 during the 2-, 5-, and 10-s contractions, respectively, at 30°C. These values are similar to or higher than those reported in the literature for isometric contractions after adjusting for temperature (assuming a Q 10 of 2.5 for myosin ATPase) (3,5,6,8,10).We find the skepticism expressed by Barclay and Loiselle and the exchange of views in these letters to be refreshing and hope that this exchange will stimulate physiologists to take a more active interest in the field of muscle energetics. Ultimately, however, independent verification in the form of hard data collected during relevantly designed experiments will be required to settle the issue.…”

supporting

confidence: 80%

Reply to Barclay and Loiselle

Zhang¹,

Andersson²,

Sandström³

et al. 2007

American Journal of Physiology-Cell Physiology

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REPLY: We appreciate the interest expressed by Drs. Barclay and Loiselle (2) in our recent paper (11). We used N-benzylp-toluene sulfonamide (BTS) to inhibit cross-bridge force production and myosin ATPase-dependent ATP splitting (measured with analytical biochemistry). BTS has been shown to inhibit cross-bridge force production and ATP splitting to comparable extents while not affecting the shape of Ca 2ϩ transients during contractions, suggesting that BTS does not affect sarcoplasmic reticulum (SR)-Ca 2ϩ release or Ca 2ϩ pumping. Under conditions of near maximal force (2 s continuous isometric contraction), cross bridges accounted for more than 50% of ATP splitting, which was consistent with the literature. Surprisingly, however, using the same experimental approach, our results indicated that cross bridges accounted for only 20% of the total ATP splitting during submaximal contractions (ϳ35% of maximal isometric force; 2-10 s continuous contractions). We suggested that ion pumps, primarily Ca 2ϩ -ATPase, accounted for the remaining ATP utilization, although this was not directly measured. We provided calculations based on stated assumptions, as well as other evidence from the literature in support of this explanation.Barclay and Loiselle (2) express skepticism regarding our suggested high relative contribution of Ca 2ϩ -pumping based on: i) heat measurements in fatigued muscles and muscles exposed to dantrolene (to inhibit SR Ca 2ϩ release); ii) estimates of Ca 2ϩ release per stimulus pulse; and iii) belief that our ATP splitting per cross bridge would be only one-quarter the value previously assumed. We address each of these points.i) Heat production occurs in proportion to the amount of ATP split, and when heat measurements are used in combination with the stretch technique, extrapolation to zero force allows for the partitioning of heat into tension-dependent (cross bridges) and tension-independent (primarily SR Ca 2ϩ -ATPase) components. Barclay (1) and Wendt and Barclay (9) used the stretch technique to study mouse extensor digitorum longus (EDL) muscles and demonstrated that the heat associated with the tension-independent component amounted to 35% of total in fatigued muscles and 42% in dantrolene-treated muscles (control ϭ 33%), respectively. These findings appear to be in disagreement with our estimate of Ca 2ϩ pumping during submaximal contractions. It should be noted, however, that the heat measurements were performed during short contraction intervals (0.2-0.5 s), whereas our measurements (using BTS) were performed during longer periods (2-10 s). Earlier studies have shown that the percent contribution of the non-tensiondependent components to ATP splitting increases as contraction duration is prolonged in mouse EDL muscles (4). Another potential factor to consider is that we used BTS, whereas the cited studies employed the stretch technique. However, why BTS and stretch would yield fairly concordant results during conditions of maximal force, but not during submaximal force, is unclear.ii) Barcla...

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“…Our model is based on earlier kinetic descriptions of the actomyosin cycle, which seek to account for both the biochemical steps and force production (for example Pate & Cooke, 1989;He et al 1998b;He et al 2000;Wang & Kawai, 2001). Unlike these models, our model includes the effects of performance of work and activation, and it describes energy production as well as the release of P i and ADP.…”

Section: Energetics: Kinetic Modelmentioning

confidence: 99%

“…This energy output comes principally from the ATPase activity of the actomyosin system and that of the sarcoplasmic reticulum Ca 2+ pump, and to a lesser extent from other energy-producing processes. Measurements of P i release by permeabilized muscle fibres have shown that the rate of the P i release step in the actomyosin cycle decreases considerably during the first few turnovers (He et al 1998b and references therein). The ADP release has been measured much later in an isometric contraction, while force is maintained at the plateau level (Hilber et al 2001); the rate is constant in this period, but much lower than that measured at the start of activation.…”

mentioning

confidence: 99%

Actomyosin energy turnover declines while force remains constant during isometric muscle contraction

West

Curtin

Ferenczi

et al. 2004

The Journal of Physiology

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Energy turnover was measured during isometric contractions of intact and Triton-permeabilized white fibres from dogfish (Scyliorhinus canicula) at 12• C. Heat + work from actomyosin in intact fibres was determined from the dependence of heat + work output on filament overlap. Inorganic phosphate (P i ) release by permeabilized fibres was recorded using the fluorescent protein MDCC-PBP, N-(2-[1-maleimidyl]ethyl)-7-diethylamino-coumarin-3 carboxamide phosphate binding protein. The steady-state ADP release rate was measured using a linked enzyme assay. The rates decreased five-fold during contraction in both intact and permeabilized fibres. In intact fibres the rate of heat + work output by actomyosin decreased from 134 ± s.e.m. 28 µW mg −1 (n = 17) at 0.055 s to 42% of this value at 0.25 s, and to 20% at 3.5 s. The force remained constant between 0.25 and 3.5 s. Similarly in permeabilized fibres the P i release rate decreased from 5.00 ± 0.39 mmol l −1 s −1 at 0.055 s to 39% of this value at 0.25 s and to 19% at 0.5 s. The steady-state ADP release rate at 15 s was 21% of the P i rate at 0.055 s. Using a single set of rate constants, the time courses of force, heat + work and P i release were described by an actomyosin model that took account of the transition from the initial state (rest or rigor) to the contracting state, shortening and the consequent work against series elasticity, and reaction heats. The model suggests that increasing P i concentration slows the cycle in intact fibres, and that changes in ATP and ADP slow the cycle in permeabilized fibres. The rate of energy output measured as heat and work decreases substantially during an isometric tetanic contraction of skeletal muscle (Abbott, 1951;Curtin & Woledge, 1979 and references therein). This energy output comes principally from the ATPase activity of the actomyosin system and that of the sarcoplasmic reticulum Ca 2+ pump, and to a lesser extent from other energy-producing processes. Measurements of P i release by permeabilized muscle fibres have shown that the rate of the P i release step in the actomyosin cycle decreases considerably during the first few turnovers (He et al. 1998b and references therein). The ADP release has been measured much later in an isometric contraction, while force is maintained at the plateau level (Hilber et al. 2001); the rate is constant in this period, but much lower than that measured at the start of activation. What is the time course of this reduction in the rate of the actomyosin cycle during an isometric contraction? Does this reduction match the change in the rate of energy release as heat + work by intact fibres?To answer these questions we have made parallel experiments using intact and permeabilized muscle fibres. White fibres from dogfish were used because both series of experiments could be made under similar conditions, including temperature (12• C). The fish were acclimated to 12• C, which is within the normal range for the natural habitat of the dogfish. Another reason for using dogfish muscle was that f...

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Rate of Phosphate Release after Photoliberation of Adenosine 5′-Triphosphate in Slow and Fast Skeletal Muscle Fibers

Cited by 26 publications

References 51 publications

Caged Protein Prenyltransferase Substrates: Tools for Understanding Protein Prenylation

Caged Protein Prenyltransferase Substrates: Tools for Understanding Protein Prenylation

Reply to Barclay and Loiselle

Actomyosin energy turnover declines while force remains constant during isometric muscle contraction

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