Characterization of a Microsecond Intermediate in the Laser Flash Photolysis of Small Phytochrome From Oat

Irradiation of small phytochrome from oat in its Pr form with 15 ns laser pulses of different wavelengths(605–655 nm) gave rise to a difference absorption with maxima at 400 and 685 nm for the first detectable transient. Bleaching of a 660 nm band was observed, non‐recuperable up to 1 ms. The transient absorption has a lifetime of 70±15 μs at 273 K. The transient is tentatively identified as lumi‐R and the conformation of its chromophore is postulated to be more extended than that of Pr. A deviation from the exponential decay of the lumi‐R absorption at 284 and 300 K and the lack of observable enhancement of the far‐red absorption within 1 ms are interpreted in terms of the appearance of still other intermediates on this time scale between lumi‐R and Pfr phytochrome.