The photocycle of phytochrome is strongly dependent on physical chemical processes occurring in its chromophore, an open-chain tetrapyrrole. Upon light excitation on the inactive form (Pr) of such bilin, an initial Z-to-E photoisomerization leads to the formation of photoproduct Lumi-R. Nonetheless, the thermal process occurring afterwards, to produce the physiological active form (Pfr), is still unclear. Hence, using computational quantum chemistry methods, we suggest that a lactam-lactim tautomerism is involved in the thermal phase of the photocycle.

Tautomerism of biliverdin in bacteriophytochrome

243rd National Meeting (2012)

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