Pyroelectric current of oriented purple membrane films.
By applying an electric field(2 to 5.5 Volt/mm) to a suspension of purple membrane from Halobacterium halobium, oriented purple-, purple blue-, and blue-colored membrane films have been formed on conductive glasses. Pyroelectric currents have been found for these three types of oriented films at temperatures between 25 and 160 degrees C. The oriented purple-colored membrane (PM) film has positive current peaks at around 60, 80, and 115 degrees C and reverses its sign at around 130 degrees C, followed by a negative peak at 145 degrees C. (Instead of the positive peak at 80 degrees C, a negative peak has been found around 90 degrees C for purple blue- and blue-colored membrane films.) The current peak at 80 degrees C for the PM film could be due to a conformational change in the protein, which includes at least a change in the environment of the chromophore. The sign-reversal current at 130 degrees C for the PM film seems to be related to denaturation of the protein. These peak temperatures in the pyroelectric current of the PM films, i.e., 60, 80, and 115 degrees C, have been found to agree well with some characteristic temperatures observed by Shnyorov et al. (D-H exchange), Jackson et al. (DSC and absorption spectra of visible light), and Hiraki et al. (X-ray, absorption spectra).
Maeda
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National Institute of Advanced Interdisciplinary Research, Ibaraki, Japan.
Katsura
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D001436:Bacteriorhodopsins / Q000737:chemistry / Q000502:physiology*; D002942:Circular Dichroism; D004558:Electric Stimulation; D019617:Halobacterium salinarum / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D013816:Thermodynamics; D013997:Time Factors
D001436:Bacteriorhodopsins