BATHOPRODUCTS AND CONFORMERS OF ALL-TRANS-BACTERIORHODOPSIN AND 13-CIS-BACTERIORHODOPSIN AT 90-K

At 90 K the photoproduct of the primary light reaction of trans-bacteriorhodopsin, the bathoproduct K(t), consists of a mixture of at least three spectrally different species, K(I)t, K(II)t and K(III)t, having maxima in the difference absorption spectra at 645, 635 and 625 nm, respectively. The bathoproducts differ in their long wavelength absorption bands and in their rate constants for photoconversion to trans-bacteriorhodopsin under far red light irradiation (lambda > 720 nm). The bathoproducts are formed from different precursors-conformers of trans-bacteriorhodopsin, which are stable at 90 K, but are in equilibrium with each other at 213 K. We suggest that the bathoproducts may initiate parallel conversion cycles of trans-bacteriorhodopsin at low temperatures. The primary photoreaction of 13-cis-bacteriorhodopsin also yields three bathoproducts, K(I)c, K(II)c and K(III), having maxima in the difference absorption spectra at 615, 605 and 595 nm, respectively.