Events in the phytochrome molecule after irradiation

Area of Science:

• Photochemistry
• Molecular Biology
• Biophysics

Background:

• Phytochrome's photoconversion from Pr to Pfr is crucial for plant photomorphogenesis.
• Previous work identified Z, E isomerization of the tetrapyrrole chromophore as a key photoreaction.

Purpose of the Study:

• To compare the Pr chromophore's conformation and configuration with those in phycocyanin.
• To investigate the roles of proton transfer and Z, E isomerization in phytochrome and phycobiliprotein photoconversion.
• To explore the heterogeneity observed in fluorescence decay kinetics of irradiated Pr.

Main Methods:

• X-ray crystallography of phycocyanin.
• Spectroscopic analysis of tetrapyrrole chromophores.
• Fluorescence decay kinetics measurements.

Main Results:

• The Z, E isomerization of the tetrapyrrole chromophore is implicated as the primary photoreaction in Pr to Pfr photoconversion.
• Proton transfer and/or Z, E isomerization are likely involved in phytochrome and phycobiliprotein photoconversion.
• Heterogeneity was observed in fluorescence decay kinetics and intermediate formation of irradiated Pr.

Conclusions:

• The study provides insights into the molecular mechanisms of phytochrome and phycobiliprotein photoreversibility.
• Understanding chromophore dynamics is essential for elucidating light-mediated signaling pathways.
• Further investigation into the heterogeneity of Pr photoreactions is warranted.