Photoelectric signals

Absorbance may be derived from the photoelectric signal either directly on a precalibrated meter scale or by a null method where a reference signal is provided optically or electrically. In null methods, readings... 

The physiological role of the ac photoelectric signal the reverse engineering visual sensory transduction process... 

It appears that the cation sensitivity and anion sensitivity of BR are mediated by separate domains of the BR molecule. The generation of AC photoelectric signals from localized domains of BR is demonstrated in an experiment in which the pH values of the two aqueous phases are varied independently [29,30] (figure 10.5). The membrane is reconstituted by means of a variant type of black lipid membrane according to the method originally developed by Drachev et al [31]. The AC photoelectric signals exhibit a positive peak and a prominent... 

THE PHYSIOLOGICAL ROLE OF THE AC PHOTOELECTRIC SIGNAL THE REVERSE ENGINEERING VISUAL SENSORY TRANSDUCTION PROCESS... 

In the example just cited, the photoelectric signal is capacitance coupled (AC coupled) to the metal electrode. The system possesses no interfacing problem. However, a number of investigators have observed that no DC photoelectric current can be observed from BR-coated metal electrode sensor systems. In... 

Michaile S and Hong F T 1994 Component analysis of the fast photoelectric signal... 

Seki A, Kubo I, Sasabe H and Tomioka H 1994 A new anion-sensitive biosensor using an ion-sensitive field effect transistor and a light-driven chloride pump, halorhodopsin Appl. Biochem. Biotechnol. 48 205-11 Fuller B E, Okajima T L and Hong F T 1995 Analysis of the d.c. photoelectric signal from model bacteriorhodopsin membranes d.c. photoconductivity determination by means of the null current method and the effect of proton ionophores Bioelectrochem. Bioenerget. 37 109-24 Cone R A 1967 Early receptor potential photoreversible charge displacement in rhodopsin Science 155 1128-31... 

Figure 3. Relaxation time course of a pulsed-light-induced photoelectric signal with a single component. Both responses to a brief light pulse and to a long rectangular light pulse are shown, but only the brief light pulse is discussed in the text. The parameter rm is the characteristic RC relaxation time of the system that depends on Rm,...

Figure 8. Photoelectric signals from a fresh (A) and an aged (B) multilayered film before and after stripping with a cotton swab. Both records are taken at 26 °C. The signal obtained after stripping is magnified 10 times in A and 6.5 times in B. Reproduced with permission from reference 42. Copyright 1989.)...

Although the visual membrane (that contains rhodopsin) does not function as a photosynthetic membrane, the fast photoelectric signal is similar and indeed analogous to the signal from a reconstituted bacteriorhodopsin membrane. In fact, the names B1 and B2 were chosen primarily on the basis of their similarity in temperature dependence to the R1 and the R2 components of the ERP, respectively Both B1 and R1 are temperature insensitive, but both B2 and R2 are inhibited by low temperature. The ERP data published by Ostrovsky s and Skulachev s groups (60, 61) suggest that the equivalent circuit model may be applicable to the analysis of the ERP. These authors considered possible physiological roles of the ERP. However, the majority of... 

Figure 13. Photoelectric signals from a Trissl-Montal-type halorhodopsin thin film. The change of the photosignal is reversible when the aqueous solution is changed from KCl to sodium citrate and vice versa. The pH was 6, and the temperature was 25 °C. The HI component has a positive polarity, and the H2 component has a negative polarity. The HI component alone appears in a multilayered dry film (not shown) and is not sensitive to the replacement of medium. (Reproduced with permission from reference 59. Copyright 1990 Institute of Electrical and Electronics Engineers, Inc.)...

Site-directed mutagenesis as applied to bacteriorhodopsin was a difficult and labor-intensive procedure that used E. coli as the expression system (79, 80). Recently, Needleman s group successfully developed a new expression system that uses a bacteriorhodopsin-deficient mutant strain of H. halobium (43, 44). Preliminary results were quite encouraging. Unlike the mutants expressed in E. coli, the new method produces mutant bacteriorhodopsins with properties that differ from the protein expressed by E. coli. Presumably this difference occurs because correct folding into three-dimensional structures is more likely in the natural host than in its surrogate. Denaturation of the mutant proteins is further avoided because reconstitution is unnecessary. Our preliminary results show that the fast photoelectric signal can be drastically altered by a judiciously chosen point mutation. 

G. Varo and L. Keszthely, Photoelectric Signals from Dried Membranes of Halobac-terium Halobium, Biophys. J. 43(1), 47-51 (1983). 

Optical absorption spectrophotometry is probably the most commonly used technique [4,a]. Reaction cells are similar to those used in flash work. Photomultipliers cover the uv-visible range the initial photoelectric signal is amplified internally, by an amoimt controlled by selection of the number of dynodes. Nanosecond equipment is commercially available. Picosecond time-resolution has been achieved [l,h]. For the infrared and Raman region, semiconductor photodiodes cover the range 400-3000 nm the vibrational spectra yield structural information about transient species much more detailed and precise than that from electronic spectra. Resonance enhancement of Raman spectra increases their intensity by a factor of 10, and makes them attractive for detection and monitoring [4,b]. They can be recorded with time-resolution down to sub-nanoseconds. Fluorescence detection is sensitive, and fast with single-photon counting or a streak camera (Section 4.2.4.2), it has been used for times down to 30 ps after an electron pulse. Conductivity also provides a fast and sensitive technique [4,c,d,l,m], especially in hydrocarbon solutions, where... 

G. Varo, L. Keszthelyi, Photoelectric signals from dried oriented purple membranes of Halobacterium halobium, Biophys. J. 43 (1983) 47-51. 

From Fig. 1 it can be seen that the time-resolved photoelectric signal induced by a picosecond flash is quite different if Qa is either oxidized or reduced. The difference is due... 

There is httle doubt that fast photoelectric signals are electrical manifestation of Hght-induced charge separation and recombination. For a macromolecule with a multistep reaction sequence as complex as rhodopsin or bacteriorhodopsin, there are many candidates for generating a fast photoelectric signal component. In principle, each step of reversible reaction can contribute a component. Fast photokinetic measurements have a tendency to pick up faster processes. We identified three fast components in reconstituted bacteriorhodopsin membranes Bl, B2, and a B2-like signal, which we called B2 component. Like B2, the B2 component is generated by interfacial proton transfer — the proton release and reuptake at the extracellular surface. This does not mean that slower components do not exist. In fact. 

Most vision researchers treat ERP as an epiphenomenon. Two reasons have often been singled out to discredit the possible physiological importance of ERP the amplitude of ERP is too small, and the ERP-like signals are ubiquitous. Shortly after the discovery of ERP, similar fast photoelectric signals were found in many different pigment-containing tissues, such as pigmented epithelia of the eyes and chloroplasts. 

Michaile, S. and Hong, F.X, Component analysis of the fast photoelectric signal from model bacteriorhodopsin membranes. Part I. Effect of multilayer stacking and prolonged drying, Bioelectrochem. Bioenerg., 33,135, 1994. 

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