Quantum efficiencies for photoconversion of bacteriorhodopsin (trans‐bR) to a bathochromic product (batho‐bR t ) and its photoreversion in purple membrane at 77 and 9 K were investigated with low temperature spectrophotometry. The kinetics of the photoconversion and its photoreversion cannot be expressed by a single exponential curve. The photoconversions at 77 and 9 K showed the same slope in the early stage. The kinetics of the photoreversions were identical at the two temperatures. These results indicate that the quantum efficiencies for the conversion of trans‐bR to batho‐bR t or for its photoreversion are identical at the two temperatures. The fact that the photoreversion cannot be expressed by a single exponential curve suggests the existence of several conformational states of batho‐bR t due to the trimer structure of the purple membrane.
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Iwasa et al. (1980) studied this question.