Bathorhodopsin

Bathorhodopsin is an ultra-short-lived photoproduct formed in vertebrate visual pigments such as rhodopsin and in related photoreceptors when light is absorbed. It arises immediately after photon absorption as the 11-cis retinal chromophore bound to the opsin isomerizes to all-trans retinal. In this intermediate, the chromophore adopts a different conformation and sits in a modified protein environment, giving bathorhodopsin a distinct absorption properties compared with the dark-state pigment.

The formation of bathorhodopsin occurs on very fast timescales, typically ranging from hundreds of femtoseconds to a few picoseconds after photon's capture. It then decays rapidly, within a few picoseconds, to subsequent intermediates such as lumirhodopsin, which precede the active signaling states of the visual cascade. The exact sequence and lifetimes can vary among species and pigments. In microbial rhodopsins like bacteriorhodopsin, a different set of intermediates (for example, K, L, M, N, O) is often described, reflecting variation in their photocycle.

Physically, bathorhodopsin represents a crucial step in the photoisomerization process that converts light energy into a biochemical signal. It is not itself the signaling state but is part of the rapid sequence that rearranges the chromophore-protein system toward the active conformation that eventually triggers downstream responses in vision. The study of bathorhodopsin, lumirhodopsin, and related intermediates has helped elucidate how protein environments influence retinal isomerization and the timing of visual signaling.