325 research outputs found
Detection of Fluorescently Labeled Actin-Bound Cross-Bridges in Actively Contracting Myofibrils
No full textAbstractMyosin subfragment 1 (S1) can be specifically modified at Lys-553 with the fluorescent probe FHS (6-[fluorescein-5(and 6)-carboxamido]hexanoic acid succinimidyl ester) (Bertrand, R., J. Derancourt, and R. Kassab. 1995. Biochemistry. 34:9500–9507), and solvent quenching of FHS-S1 with iodide has been shown to be sensitive to actin binding at low ionic strength (MacLean, Chrin, and Berger, 2000. Biophys. J. 000–000). In order to extend these results and examine the fraction of actin-bound myosin heads within the myofilament lattice during calcium activation, we have modified skeletal muscle myofibrils, mildly cross-linked with EDC (1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide) to prevent shortening, with FHS. The myosin heavy chain appears to be the predominant site of labeling, and the iodide quenching patterns are consistent with those obtained for myosin S1 in solution, suggesting that Lys-553 is indeed the primary site of FHS incorporation in skeletal muscle myofibrils. The iodide quenching results from calcium-activated FHS-myofibrils indicate that during isometric contraction 29% of the myosin heads are strongly bound to actin within the myofilament lattice at low ionic strength. These results suggest that myosin can be specifically modified with FHS in more complex and physiologically relevant preparations, allowing the real time examination of cross-bridge interactions with actin in in vitro motility assays and during isometric and isotonic contractions within single muscle fibers
A study of the difference in charged multiplicity between bottom and light quark initialed events
No full textUpon the determination of heavy quark fragmentation functions in annihilation
No full textResults on the fragmentation of heavy quarks from analyses of inclusive lepton production in e e annihilation are studied. The use of various fragmentation variables is closely examined and their differences resolved, providing a common basis for comparison of experimental results. The mean value of the fraction of available energy-momentum carried by the primary heavy hadron, defined as z=, is determined to be 〈z〉=0.67±0.02±0.02 and 〈z〉b=0.83±0.01±0.02 for an unknown mixture of charmed and bottom flavoured hadrons respectively. The corresponding values of the parameterɛQ of the Peterson fragmentation function are ε=0.06 and ε=0.06. The ratioɛ c/ɛ can be approximately related to Mb/Mc giving a value of 10, in agreement with an expectation of ∼10. Measurements of the charged multiplicity of hadronic events containing heavy quark jets are investigated in terms of the mean value of z
Chirped and modulated electron pulse free electron laser techniques
No full textA potential method to improve the free electron laser’s output when the electron pulse has a large energy spread is investigate and results presented. A simplified model is the first given, in which there are a number of linearly chirped beamlets equally separated in energy and time. By using chicanes, radiation from one chirped beamlet is passed to the next, helping to negate the effect of the beamlet chirps and maintaining resonant interactions. Hence the addition of chicane allow the electrons to interact with a smaller range of frequencies (Δω<2ργr), sustaining the FEL interaction. One method to generate such a beamlet structure is presented and is shown to increase FEL performance by two orders of magnitude
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