47 research outputs found
Early Receptor Potentials of Rods and Cones in Rodents
The second phase (negative peak) of the early receptor potential of cones has been
studied in the all-cone eyes of the Mexican and antelope ground squirrels
(Citellus mexicanus and Citellus leucurus) and
compared with responses from the rod-dominant eyes of the rat and flying squirrel
(Glaucomys volans). The responses obtained from the all-cone eyes
tended to be smaller in amplitude, to have higher thresholds, and to be considerably more
resistant to light adaptation than the responses from the rod-dominant eyes. The wave
forms and time courses of the two types of responses were similar, although the cone
potential tended to be less sensitive to temperature variations and its time constants
tended to be shorter than those of the rod potential. The spectral sensitivity of the
second phase of the early receptor potential of the Mexican ground squirrel closely
follows the absorption spectrum of a Dartnall nomogram pigment having its absorption
maximum at 540 mμ. Moreover, as in the case of the rat, the
amplitude of the response appears to be linearly related to the amount of pigment bleached
in a flash. Thus, in both all-rod and all-cone systems the early receptor potential
appears to arise in the photoexcitation of the respective visual pigment and appears to be
closely linked to the initial photochemical events. The similarity of the wave form, time
course, and stimulus-response curves in the two systems suggests that the early receptor
potential is produced by similar mechanisms in all-rod and all-cone systems
A ‘Third Culture’ in Economics? An Essay on Smith, Confucius and the Rise of China
The role of the protein in the photochemistry of the retinal chromophore of visual pigments and the purple membrane protein
Molecular Basis of Spectral Tuning in the Newt Short Wavelength Sensitive Visual Pigment â€
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Molecular mechanisms controlling proton pumping by bacteriorhodopsin. Final report
Bacteriorhodopsin (bR) is the simplest biological system for the transduction of light energy. Light energy is directly converted to transmembrane proton gradient by a single, small membrane protein. The extraordinary stability of bR makes it an outstanding subject for bioenergetic studies. This project has focused on the role of interactions between key residues of the pigment involved in light-induced proton transfer. Methods to estimate the strength of these interactions and their correlation with the rate and efficiency of proton transfer have been developed. The concept of the coupling of the protonation states of key groups has been applied to individual steps of the proton transfer with the ultimate goal of understanding on the molecular level the driving forces for proton transport and the pathway of the transported proton in bT. The mechanism of light-induced proton release, uptake and the mechanism of recovery of initial state of bT has been examined. The experiments were performed with genetically engineered, site-specific mutants of bR. This has enabled us to characterize the role of individual amino acid residues in bR. Time resolved and low temperature absorption spectroscopy and light-induced photocurrent measurements were used in order to study the photochemical cycle and proton transfer in mutant pigments. Chemical modification and crosslinking of both the specific amino acids to the chromophore or to other amino acids were used to elucidate the role of light-induced conformational changes in the photocycle and the structure of the protein in the ground state. The results of this project provided new knowledge on the architecture of the proton transfer pathways inside the protein, on the mechanism of proton release in bR, and on the role of specific amino acid residues in the structure and function of bR