No abstract

We used a gated optical multichannel analyzer to measure transient flash-induced absorption changes in bacteriorhodopsin (BR) and halorhodopsin (HR) and developed criteria for calculating the absorption spectra of the photocycle intermediates and the kinetics of their rise and decay. The results for BR agree with data reported by a large number of other authors. The results for HR in the presence of chloride are consistent with earlier data and reveal an additional intermediate, not previously seen, in the submicrosecond time scale. Although an M412-like intermediate is not in the HR photocycle, a one-by-one comparison of the rest of the intermediates observed for BR and HR indicates a striking similarity between the photocycles of the two bacterial rhodopsins. This was previously not apparent, perhaps because the experimental approaches to the spectroscopy of the two pigments were different and the data were thus more fragmented.

No abstract

The kinetics of the photoreceptor potential of phototaxis in biflagellated green alga Haematococcus pluvialis in response to a 10-ns laser pulse of three wavelengths (465, 550, and 590 nm) were measured in single cells with 30 mus time resolution. The rise and the decay of photoinduced potential are both at least biphasic. The first component of the rise is very stable and has no measurable (<30 mus) time delay. The second component is triggered after a 120-400-mus lag period, depending on flash intensity. Its appearance is sensitive to the physiological state of the cell and the amplitude can be increased by phototactically ineffective red background illumination. The electrical generators for both components are localized in the same region of the cell membrane (on the stigma-bearing side) and these components have the same depolarizing sign. The results indicate that the photoreceptor potential in phototaxis comprises two components, which could be interpreted as light-induced charge movement within the photoreceptor molecules and changes in ion permeability of the cell membrane.

The permanent dipole moment, polarizability, and the retinal angle of Halobacterium halobium purple membranes were determined at different pH values. All of the parameters have a maximum between pH 5 and 6. There is a reversal in the direction of the permanent dipole moment near pH 5. The value of permanent dipole moment was determined to be 60 D/protein at pH 6.6, and the value obtained for polarizability was 3 X 10(-28) Fm2/membrane fragment. The retinal angle of all-trans retinal was 0.8 degrees smaller than that of the 13-cis conformation.