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Time-resolved absorption measurements are performed on the forward phototransformation of native oat phytochrome at 10 degrees C. Likewise, laser photolysis allows for the measurement of the transient difference absorption spectra at delay times from 100 ns to 800 ms. A global fitting algorithm, together with a singular value decomposition method, is used to evaluate the absorption changes at different wavelengths which follow the same kinetics.

The time-resolved circular dichroism (TRCD) spectra of the intermediates formed during the Pr -> Pfr phototransformation in native oat phytochrome is measured at 10 degrees C. The spectra shows the presence of the lumi-R intermediate whose TRCD spectrum is substantially different from its steady-state CD spectrum at low temperature. This discrepancy may be due to different protein-chromophore interactions. It is proposed that the lumi-R trapped in the low-temperature experiment is an unrelaxed isomerized species.