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The phototransformation kinetics of native oat phytochrome from etiolated seedling shoots of Avena sativa was investigated by laser photolysis experiments at 10 o C. The phototransformation from the red-absorbing form (Pr) to the far-red-absorbing form (Pfr) was initiated by 7-ns (fwhm) laser pulses at 638 nm. The transient absorption difference spectra in the UV and visible regions were recorded from 100 ns to 800 ms after photolysis by a gated optical multichannel analyzer system. A global fitting procedure employing a singular value decomposition method was used to simultaneously analyze the difference spectra at various times after photolysis

Time-resolved circular dichroism (TRCD) spectral studies of the Pr→Pfr phototransformation in native oat phytochrome (124 kDa) were performed in the 500-800 nm spectral region from 500 ns to 500 ms after photolysis at 10 o C. The first intermediate observed in our measurements, lumi-R, had an absorption maximum at 695 nm, but its difference TRCD spectrum showed a CD maximum near 660 nm. This result differed from results of previous steady-state CD measurements where the intermediates of the photoconversion were trapped at low temperatures