Timing Performance of Ge(Li) Detectors

Miehé, J.A.; Siffert, P.

doi:10.1109/tns.1970.4325745

Cited by 9 publications

(1 citation statement)

References 12 publications

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“…The conditions of measurements were the same as those given in our preceding paper [8] except that we applied the amplitude selection of anode pulses, which allowed a high photoelectron counting rate to be used with an R.C.A. 8850 photomultiplier as a detector [27]. Consequently the linear combinations of the transient polarized fluorescence ill ( t ) and il ( t ) had to be written [28] as follows:…”

Section: Pulse Fluorimetrymentioning

confidence: 99%

Anisotropy Decay of Labelled Actin

Ikkai

Wahl

Auchet

1979

European Journal of Biochemistry

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G actin, labelled presumably on cysteine-373 with the fluorescent chromophore N-iodoacetyl-N'-(5 sulfo-1 -naphthyl)-ethylenediamine and purified by Sephacryl S-200 gel chromatography, migrated in one band on polyacrylamide gel electrophoresis and had the same polymerizability as unlabelled purified G actin. Anisotropy decays of labelled actin solutions have been studied at different ionic strengths and protein concentrations.It was found that these anisotropy decays could be fitted by a sum' of two exponential functions. Under low ionic strength or below the critical concentrations the longer correlation time (45 ns at 3.5 " C ) was independent of protein concentration and ionic strength. Above the critical concentration, the longer correlation time increased with ionic strength and protein concentration. In order to take into account that, under these conditions, the solutions contained a mixture of F and G actin at the critical concentration, the anisotropy decays were analysed as a sum of three exponential functions in which the longest correlation time characterized F actin. Since F actin correlation time also depended on actin concentration, an analysis with a sum of four exponential functions was performed, in which two fixed correlation times (100 ns and 900 ns at 3.5 "C) were introduced in order to characterize the F actin motions. The longer of these correlation times was attributed to regions where two actin filaments interact side by side, while the shorter one was attributed to filament regions free from intermolecular interactions.The small value of the free F actin correlation time indicates that the protomer peptide chain is very flexible around its C terminus, probably involving the motion of a molecular lobe. This flexibility might be an important factor in the interaction of actin with myosin during the muscular contraction.During muscular contraction, the globular heads of the myosin molecules which constitute the thick filament, interact cyclically with the actin protomers in the thin filaments [l].The thin filament also includes troponin and tropomyosin, the regulatory proteins which control the myosin-actin interaction, according to the calcium ion concentration in the cell [2]. Tropomyosin has been shown to lie along the grooves of the double-helix structure formed by the actin protomers in the filament. According to X-ray diffraction experiments, its position differs in the relaxed and the contracting states of the muscle [3]. The regulatory mechanism associated with this motion of tropomyosin has been explained by the steric blocking model [4], in which actin does not play an active role.Actin can be extracted from muscles with a lowionic-strength solvent in which this protein is dispersed as monomer molecules (G actin). If one increases the ionic strength, actin polymerizes in helical aggregates (F actin) [4]. F actin forms complexes with tropomyosin and troponin in which the arrangement of these molecules is the same as in the thin muscle filaments. Studies of these reconstituted filam...

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Section: Pulse Fluorimetrymentioning

confidence: 99%