Actinic detectors

So far the effect of changing albedo was discussed only on global irradiance, that means on horizontal detector surfaces. If the surface is tilted or if actinic detectors (2n or 4k) are used, then significantly higher effects due to high albedo have to be expected. 

Fig. 9.4 Establishment of the quantitative methylation-specific polymerase chain reaction (MSP) analytical procedure. The ABI PRISM 7900 HT Sequence Detector system was used to perform real-time polymerase chain reaction (PCR) using MSP primers and bisulfite-modified template DNA. Upper panels Setting up the conditions to obtain the standard curves with 50% (A) or 25% (B) sequential dilution of the template. Lower panels The amplification curves on the left represent P-actin, unmethylated, and methylated MSP products, respectively, for reelin (RELN) (C). Amplification curves were compared at the set threshold before 40 cycles. Amplification curves from various samples are shown in the lower panel right (D)...

The filament is lowered onto a stationary silica bead sparsely coated with HMM fragments of myosin. In the presence of ATP the myosin heads bind transiently for a few milliseconds to the actin, moving it in one direction and displacing the beads from their positions in the optical traps. An image of one of the beads is projected onto photodiode detectors capable of measuring small displacements. The displacing force can also be recorded. For details of the experiments and of the optical traps and measuring devices see Finer et al.200 Courtesy of J. A. Spudich. 

Together, these two assays opened up new avenues of research into actin and myosin interaction. Two different adaptations of the assay allow for the measurement of force by small numbers of myosin molecules (Kishino and Yanagida, 1988 Finer et al., 1994). The first of these uses a flexible, calibrated microneedle to which an actin filament is attached. The deflection of the needle as myosin moves the actin filament can be measured to determine the force (Kishino and Yanagida, 1988). In the second adaptation, an optical trap (Block, 1990) is used to measure both the force and step size of single myosin molecules (Finer etal., 1994). Beads are attached to each end of an actin filament. Dual optical traps position the beads (and thus the actin filament) in the vicinity of a single or a few myosin molecules. A sensitive quadrant detector is used to detect the position of the bead as myosin moves the actin filament. 

FIGURE 1 Schematic drawing of the measuring chamber. Inlet and outlet for (A) the bacterial suspension, (B) the circulating medium, (C) dialysis membrane, (D) cavities for thermostat water, (E) drive to adjust the thickness of the suspension layer, (F) bifurcated fibre optics connected to (G) the LED and photodiode detector and to (H) the two actinic light sources. FIGURE 2 Fluorescence transients measured in a cell suspension with (1) and without (2) bubbling with N2+CO2. R. rubrum SI, MOPS buffer, 25 C, 100 W.m-2. 

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